diff --git a/.github/test-ci-locally.ps1 b/.github/test-ci-locally.ps1 new file mode 100644 index 0000000..fbdb1ae --- /dev/null +++ b/.github/test-ci-locally.ps1 @@ -0,0 +1,141 @@ +# Local CI/CD Testing Script +# This script replicates the GitHub Actions workflow locally for testing + +Write-Host "========================================" -ForegroundColor Cyan +Write-Host "SlidingWindowCache CI/CD Local Test" -ForegroundColor Cyan +Write-Host "========================================" -ForegroundColor Cyan +Write-Host "" + +# Environment variables (matching GitHub Actions) +$env:SOLUTION_PATH = "SlidingWindowCache.sln" +$env:PROJECT_PATH = "src/SlidingWindowCache/SlidingWindowCache.csproj" +$env:WASM_VALIDATION_PATH = "src/SlidingWindowCache.WasmValidation/SlidingWindowCache.WasmValidation.csproj" +$env:UNIT_TEST_PATH = "tests/SlidingWindowCache.Unit.Tests/SlidingWindowCache.Unit.Tests.csproj" +$env:INTEGRATION_TEST_PATH = "tests/SlidingWindowCache.Integration.Tests/SlidingWindowCache.Integration.Tests.csproj" +$env:INVARIANTS_TEST_PATH = "tests/SlidingWindowCache.Invariants.Tests/SlidingWindowCache.Invariants.Tests.csproj" + +# Track failures +$failed = $false + +# Step 1: Restore solution dependencies +Write-Host "[Step 1/9] Restoring solution dependencies..." -ForegroundColor Yellow +dotnet restore $env:SOLUTION_PATH +if ($LASTEXITCODE -ne 0) { + Write-Host "❌ Restore failed" -ForegroundColor Red + $failed = $true +} +else { + Write-Host "✅ Restore successful" -ForegroundColor Green +} +Write-Host "" + +# Step 2: Build solution +Write-Host "[Step 2/9] Building solution (Release)..." -ForegroundColor Yellow +dotnet build $env:SOLUTION_PATH --configuration Release --no-restore +if ($LASTEXITCODE -ne 0) { + Write-Host "❌ Build failed" -ForegroundColor Red + $failed = $true +} +else { + Write-Host "✅ Build successful" -ForegroundColor Green +} +Write-Host "" + +# Step 3: Validate WebAssembly compatibility +Write-Host "[Step 3/9] Validating WebAssembly compatibility..." -ForegroundColor Yellow +dotnet build $env:WASM_VALIDATION_PATH --configuration Release --no-restore +if ($LASTEXITCODE -ne 0) { + Write-Host "❌ WebAssembly validation failed" -ForegroundColor Red + $failed = $true +} +else { + Write-Host "✅ WebAssembly compilation successful - library is compatible with net8.0-browser" -ForegroundColor Green +} +Write-Host "" + +# Step 4: Run Unit Tests +Write-Host "[Step 4/9] Running Unit Tests with coverage..." -ForegroundColor Yellow +dotnet test $env:UNIT_TEST_PATH --configuration Release --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults/Unit +if ($LASTEXITCODE -ne 0) { + Write-Host "❌ Unit tests failed" -ForegroundColor Red + $failed = $true +} +else { + Write-Host "✅ Unit tests passed" -ForegroundColor Green +} +Write-Host "" + +# Step 5: Run Integration Tests +Write-Host "[Step 5/9] Running Integration Tests with coverage..." -ForegroundColor Yellow +dotnet test $env:INTEGRATION_TEST_PATH --configuration Release --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults/Integration +if ($LASTEXITCODE -ne 0) { + Write-Host "❌ Integration tests failed" -ForegroundColor Red + $failed = $true +} +else { + Write-Host "✅ Integration tests passed" -ForegroundColor Green +} +Write-Host "" + +# Step 6: Run Invariants Tests +Write-Host "[Step 6/9] Running Invariants Tests with coverage..." -ForegroundColor Yellow +dotnet test $env:INVARIANTS_TEST_PATH --configuration Release --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults/Invariants +if ($LASTEXITCODE -ne 0) { + Write-Host "❌ Invariants tests failed" -ForegroundColor Red + $failed = $true +} +else { + Write-Host "✅ Invariants tests passed" -ForegroundColor Green +} +Write-Host "" + +# Step 7: Check coverage files +Write-Host "[Step 7/9] Checking coverage files..." -ForegroundColor Yellow +$coverageFiles = Get-ChildItem -Path "./TestResults" -Filter "coverage.cobertura.xml" -Recurse +if ($coverageFiles.Count -gt 0) { + Write-Host "✅ Found $($coverageFiles.Count) coverage file(s)" -ForegroundColor Green + foreach ($file in $coverageFiles) { + Write-Host " - $($file.FullName)" -ForegroundColor Gray + } +} +else { + Write-Host "⚠️ No coverage files found" -ForegroundColor Yellow +} +Write-Host "" + +# Step 8: Build NuGet package +Write-Host "[Step 8/9] Creating NuGet package..." -ForegroundColor Yellow +if (Test-Path "./artifacts") { + Remove-Item -Path "./artifacts" -Recurse -Force +} +dotnet pack $env:PROJECT_PATH --configuration Release --no-build --output ./artifacts +if ($LASTEXITCODE -ne 0) { + Write-Host "❌ Package creation failed" -ForegroundColor Red + $failed = $true +} +else { + $packages = Get-ChildItem -Path "./artifacts" -Filter "*.nupkg" + Write-Host "✅ Package created successfully" -ForegroundColor Green + foreach ($pkg in $packages) { + Write-Host " - $($pkg.Name)" -ForegroundColor Gray + } +} +Write-Host "" + +# Step 9: Summary +Write-Host "========================================" -ForegroundColor Cyan +Write-Host "Test Summary" -ForegroundColor Cyan +Write-Host "========================================" -ForegroundColor Cyan +if ($failed) { + Write-Host "❌ Some steps failed - see output above" -ForegroundColor Red + exit 1 +} +else { + Write-Host "✅ All steps passed successfully!" -ForegroundColor Green + Write-Host "" + Write-Host "Next steps:" -ForegroundColor Cyan + Write-Host " - Review coverage reports in ./TestResults/" -ForegroundColor Gray + Write-Host " - Inspect NuGet package in ./artifacts/" -ForegroundColor Gray + Write-Host " - Push to trigger GitHub Actions workflow" -ForegroundColor Gray + exit 0 +} diff --git a/.github/workflows/slidingwindowcache.yml b/.github/workflows/slidingwindowcache.yml new file mode 100644 index 0000000..b9a0542 --- /dev/null +++ b/.github/workflows/slidingwindowcache.yml @@ -0,0 +1,105 @@ +name: CI/CD - SlidingWindowCache + +on: + push: + branches: [ master, main ] + paths: + - 'src/SlidingWindowCache/**' + - 'src/SlidingWindowCache.WasmValidation/**' + - 'tests/**' + - '.github/workflows/slidingwindowcache.yml' + pull_request: + branches: [ master, main ] + paths: + - 'src/SlidingWindowCache/**' + - 'src/SlidingWindowCache.WasmValidation/**' + - 'tests/**' + - '.github/workflows/slidingwindowcache.yml' + workflow_dispatch: + +env: + DOTNET_VERSION: '8.x.x' + SOLUTION_PATH: 'SlidingWindowCache.sln' + PROJECT_PATH: 'src/SlidingWindowCache/SlidingWindowCache.csproj' + WASM_VALIDATION_PATH: 'src/SlidingWindowCache.WasmValidation/SlidingWindowCache.WasmValidation.csproj' + UNIT_TEST_PATH: 'tests/SlidingWindowCache.Unit.Tests/SlidingWindowCache.Unit.Tests.csproj' + INTEGRATION_TEST_PATH: 'tests/SlidingWindowCache.Integration.Tests/SlidingWindowCache.Integration.Tests.csproj' + INVARIANTS_TEST_PATH: 'tests/SlidingWindowCache.Invariants.Tests/SlidingWindowCache.Invariants.Tests.csproj' + +jobs: + build-and-test: + runs-on: ubuntu-latest + + steps: + - name: Checkout code + uses: actions/checkout@v4 + + - name: Setup .NET + uses: actions/setup-dotnet@v4 + with: + dotnet-version: ${{ env.DOTNET_VERSION }} + + - name: Restore solution dependencies + run: dotnet restore ${{ env.SOLUTION_PATH }} + + - name: Build solution + run: dotnet build ${{ env.SOLUTION_PATH }} --configuration Release --no-restore + + - name: Validate WebAssembly compatibility + run: | + echo "::group::WebAssembly Validation" + echo "Building SlidingWindowCache.WasmValidation for net8.0-browser target..." + dotnet build ${{ env.WASM_VALIDATION_PATH }} --configuration Release --no-restore + echo "✅ WebAssembly compilation successful - library is compatible with net8.0-browser" + echo "::endgroup::" + + - name: Run Unit Tests with coverage + run: dotnet test ${{ env.UNIT_TEST_PATH }} --configuration Release --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults/Unit + + - name: Run Integration Tests with coverage + run: dotnet test ${{ env.INTEGRATION_TEST_PATH }} --configuration Release --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults/Integration + + - name: Run Invariants Tests with coverage + run: dotnet test ${{ env.INVARIANTS_TEST_PATH }} --configuration Release --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults/Invariants + + - name: Upload coverage reports to Codecov + uses: codecov/codecov-action@v4 + with: + files: ./TestResults/**/coverage.cobertura.xml + fail_ci_if_error: false + verbose: true + flags: unittests,integrationtests,invarianttests + env: + CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }} + + publish-nuget: + runs-on: ubuntu-latest + needs: build-and-test + if: github.event_name == 'push' && (github.ref == 'refs/heads/main' || github.ref == 'refs/heads/master') + + steps: + - name: Checkout code + uses: actions/checkout@v4 + + - name: Setup .NET + uses: actions/setup-dotnet@v4 + with: + dotnet-version: ${{ env.DOTNET_VERSION }} + + - name: Restore dependencies + run: dotnet restore ${{ env.PROJECT_PATH }} + + - name: Build SlidingWindowCache + run: dotnet build ${{ env.PROJECT_PATH }} --configuration Release --no-restore + + - name: Pack SlidingWindowCache + run: dotnet pack ${{ env.PROJECT_PATH }} --configuration Release --no-build --output ./artifacts + + - name: Publish SlidingWindowCache to NuGet + run: dotnet nuget push ./artifacts/SlidingWindowCache.*.nupkg --api-key ${{ secrets.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate + + - name: Upload package artifacts + uses: actions/upload-artifact@v4 + with: + name: slidingwindowcache-package + path: ./artifacts/*.nupkg diff --git a/README.md b/README.md new file mode 100644 index 0000000..0e1422c --- /dev/null +++ b/README.md @@ -0,0 +1,520 @@ +# Sliding Window Cache + +**A read-only, range-based, sequential-optimized cac~~~~he with background rebalancing and cancellation-aware prefetching.** + +--- + +[![CI/CD](https://github.com/blaze6950/SlidingWindowCache/actions/workflows/slidingwindowcache.yml/badge.svg)](https://github.com/blaze6950/SlidingWindowCache/actions/workflows/slidingwindowcache.yml) +[![NuGet](https://img.shields.io/nuget/v/SlidingWindowCache.svg)](https://www.nuget.org/packages/SlidingWindowCache/) +[![NuGet Downloads](https://img.shields.io/nuget/dt/SlidingWindowCache.svg)](https://www.nuget.org/packages/SlidingWindowCache/) +[![codecov](https://codecov.io/gh/blaze6950/SlidingWindowCache/graph/badge.svg?token=RFQBNX7MMD)](https://codecov.io/gh/blaze6950/SlidingWindowCache) +[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT) +[![.NET 8.0](https://img.shields.io/badge/.NET-8.0-blue.svg)](https://dotnet.microsoft.com/download/dotnet/8.0) + +--- + +## 📑 Table of Contents + +- [Overview](#-overview) +- [Sliding Window Cache Concept](#-sliding-window-cache-concept) +- [Understanding the Sliding Window](#-understanding-the-sliding-window) +- [Materialization for Fast Access](#-materialization-for-fast-access) +- [Usage Example](#-usage-example) +- [Configuration](#-configuration) +- [Optional Diagnostics](#-optional-diagnostics) +- [Documentation](#-documentation) +- [Performance Considerations](#-performance-considerations) +- [CI/CD & Package Information](#-cicd--package-information) +- [Contributing & Feedback](#-contributing--feedback) +- [License](#license) + +--- + +## 📦 Overview + +The Sliding Window Cache is a high-performance caching library designed for scenarios where data is accessed in sequential or predictable patterns across ranges. It automatically prefetches and maintains a "window" of data around the most recently requested range, significantly reducing the need for repeated data source queries. + +### Key Features + +- **Automatic Prefetching**: Intelligently prefetches data on both sides of requested ranges based on configurable coefficients +- **Background Rebalancing**: Asynchronously adjusts the cache window when access patterns change, with debouncing to avoid thrashing +- **Cancellation-Aware**: Full support for `CancellationToken` throughout the async pipeline +- **Range-Based Operations**: Built on top of the [`Intervals.NET`](https://github.com/blaze6950/Intervals.NET) library for robust range handling +- **Configurable Read Modes**: Choose between different materialization strategies based on your performance requirements +- **Optional Diagnostics**: Built-in instrumentation for monitoring cache behavior and validating system invariants + +--- + +## 🎯 Sliding Window Cache Concept + +Traditional caches work with individual keys. A sliding window cache, in contrast, operates on **continuous ranges** of data: + +1. **User requests a range** (e.g., records 100-200) +2. **Cache fetches more than requested** (e.g., records 50-300) based on configured left/right cache coefficients +3. **Subsequent requests within the window are served instantly** from materialized data +4. **Window automatically rebalances** when the user moves outside threshold boundaries + +This pattern is ideal for: + +- Time-series data (sensor readings, logs, metrics) +- Paginated datasets with forward/backward navigation +- Sequential data processing (video frames, audio samples) +- Any scenario with high spatial or temporal locality of access + +--- + +## 🔍 Understanding the Sliding Window + +### Visual: Requested Range vs. Cache Window + +When you request a range, the cache actually fetches and stores a larger window: + +``` +Requested Range (what user asks for): + [======== USER REQUEST ========] + +Actual Cache Window (what cache stores): + [=== LEFT BUFFER ===][======== USER REQUEST ========][=== RIGHT BUFFER ===] + ← leftCacheSize requestedRange size rightCacheSize → +``` + +The **left** and **right buffers** are calculated as multiples of the requested range size using the `leftCacheSize` and `rightCacheSize` coefficients. + +### Visual: Rebalance Trigger + +Rebalancing occurs when a new request moves outside the threshold boundaries: + +``` +Current Cache Window: +[========*===================== CACHE ======================*=======] + ↑ ↑ + Left Threshold (20%) Right Threshold (20%) + +Scenario 1: Request within thresholds → No rebalance +[========*===================== CACHE ======================*=======] + [---- new request ----] ✓ Served from cache + +Scenario 2: Request outside threshold → Rebalance triggered +[========*===================== CACHE ======================*=======] + [---- new request ----] + ↓ + 🔄 Rebalance: Shift window right +``` + +### Visual: Configuration Impact + +How coefficients control the cache window size: + +``` +Example: User requests range of size 100 + +leftCacheSize = 1.0, rightCacheSize = 2.0 +[==== 100 ====][======= 100 =======][============ 200 ============] + Left Buffer Requested Range Right Buffer + +Total Cache Window = 100 + 100 + 200 = 400 items + +leftThreshold = 0.2 (20% of 400 = 80 items) +rightThreshold = 0.2 (20% of 400 = 80 items) +``` + +**Key insight:** Threshold percentages are calculated based on the **total cache window size**, not individual buffer sizes. + +--- + +## 💾 Materialization for Fast Access + +### Why Materialization? + +The cache **always materializes** the data it fetches, meaning it stores the data in memory in a directly accessible format (arrays or lists) rather than keeping lazy enumerables. This design choice ensures: + +- **Fast, predictable read performance**: No deferred execution chains on the hot path +- **Multiple reads without re-enumeration**: The same data can be read many times at zero cost (in Snapshot mode) +- **Clean separation of concerns**: Data fetching (I/O-bound) is decoupled from data serving (CPU-bound) + +### Read Modes: Snapshot vs. CopyOnRead + +The cache supports two materialization strategies, configured at creation time via the `UserCacheReadMode` enum: + +#### Snapshot Mode (`UserCacheReadMode.Snapshot`) + +**Storage**: Contiguous array (`TData[]`) +**Read behavior**: Returns `ReadOnlyMemory` pointing directly to internal array +**Rebalance behavior**: Always allocates a new array + +**Advantages:** +- ✅ **Zero allocations on read** – no memory overhead per request +- ✅ **Fastest read performance** – direct memory view +- ✅ Ideal for **read-heavy scenarios** with frequent access to cached data + +**Disadvantages:** +- ❌ **Expensive rebalancing** – always allocates a new array, even if size is unchanged +- ❌ **Large Object Heap (LOH) pressure** – arrays ≥85,000 bytes go to LOH, which can cause fragmentation +- ❌ Higher memory usage during rebalance (old + new arrays temporarily coexist) + +**Best for:** +- Applications that read the same data many times +- Scenarios where cache updates are infrequent relative to reads +- Systems with ample memory and minimal LOH concerns + +#### CopyOnRead Mode (`UserCacheReadMode.CopyOnRead`) + +**Storage**: Growable list (`List`) +**Read behavior**: Allocates a new array and copies the requested range +**Rebalance behavior**: Uses `List` operations (Clear + AddRange) + +**Advantages:** +- ✅ **Cheaper rebalancing** – `List` can grow without always allocating large arrays +- ✅ **Reduced LOH pressure** – avoids large contiguous allocations in most cases +- ✅ Ideal for **memory-sensitive scenarios** or when rebalancing is frequent + +**Disadvantages:** +- ❌ **Allocates on every read** – new array per request +- ❌ **Copy overhead** – data must be copied from list to array +- ❌ Slower read performance compared to Snapshot mode + +**Best for:** +- Applications with frequent cache rebalancing +- Memory-constrained environments +- Scenarios where each range is typically read once or twice +- Systems sensitive to LOH fragmentation + +### Choosing a Read Mode + +| Scenario | Recommended Mode | +|-----------------------------------------------------|------------------| +| High read-to-rebalance ratio (e.g., 100:1) | **Snapshot** | +| Frequent rebalancing (e.g., random access patterns) | **CopyOnRead** | +| Large cache sizes (>85KB arrays) | **CopyOnRead** | +| Read-once patterns | **CopyOnRead** | +| Repeated reads of the same range | **Snapshot** | +| Memory-constrained systems | **CopyOnRead** | + +**For detailed comparison and multi-level cache composition patterns, see [Storage Strategies Guide](docs/storage-strategies.md).** + +--- + +## 🚀 Usage Example + +```csharp +using SlidingWindowCache; +using SlidingWindowCache.Configuration; +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; + +// Configure the cache behavior +var options = new WindowCacheOptions( + leftCacheSize: 1.0, // Cache 100% of requested range size to the left + rightCacheSize: 2.0, // Cache 200% of requested range size to the right + leftThreshold: 0.2, // Rebalance if <20% left buffer remains + rightThreshold: 0.2 // Rebalance if <20% right buffer remains +); + +// Create cache with Snapshot mode (zero-allocation reads) +var cache = WindowCache.Create( + dataSource: myDataSource, + domain: new IntegerFixedStepDomain(), + options: options, + readMode: UserCacheReadMode.Snapshot +); + +// Request data - returns ReadOnlyMemory +var data = await cache.GetDataAsync( + Range.Closed(100, 200), + cancellationToken +); + +// Access the data +foreach (var item in data.Span) +{ + Console.WriteLine(item); +} +``` + +--- + +## ⚙️ Configuration + +The `WindowCacheOptions` class provides fine-grained control over cache behavior. Understanding these parameters is essential for optimal performance. + +### Configuration Parameters + +#### Cache Size Coefficients + +**`leftCacheSize`** (double, default: 1.0) +- **Definition**: Multiplier applied to the requested range size to determine the left buffer size +- **Practical meaning**: How much data to prefetch *before* the requested range +- **Example**: If user requests 100 items and `leftCacheSize = 1.5`, the cache prefetches 150 items to the left +- **Typical values**: 0.5 to 2.0 (depending on backward navigation patterns) + +**`rightCacheSize`** (double, default: 2.0) +- **Definition**: Multiplier applied to the requested range size to determine the right buffer size +- **Practical meaning**: How much data to prefetch *after* the requested range +- **Example**: If user requests 100 items and `rightCacheSize = 2.0`, the cache prefetches 200 items to the right +- **Typical values**: 1.0 to 3.0 (higher for forward-scrolling scenarios) + +#### Threshold Policies + +**`leftThreshold`** (double, default: 0.2) +- **Definition**: Percentage of the **total cache window size** that triggers rebalancing when crossed on the left +- **Calculation**: `leftThreshold × (Left Buffer + Requested Range + Right Buffer)` +- **Example**: With total window of 400 items and `leftThreshold = 0.2`, rebalance triggers when user moves within 80 items of the left edge +- **Typical values**: 0.15 to 0.3 (lower = more aggressive rebalancing) + +**`rightThreshold`** (double, default: 0.2) +- **Definition**: Percentage of the **total cache window size** that triggers rebalancing when crossed on the right +- **Calculation**: `rightThreshold × (Left Buffer + Requested Range + Right Buffer)` +- **Example**: With total window of 400 items and `rightThreshold = 0.2`, rebalance triggers when user moves within 80 items of the right edge +- **Typical values**: 0.15 to 0.3 (lower = more aggressive rebalancing) + +**⚠️ Critical Understanding**: Thresholds are **NOT** calculated against individual buffer sizes. They represent a percentage of the **entire cache window** (left buffer + requested range + right buffer). See [Understanding the Sliding Window](#-understanding-the-sliding-window) for visual examples. + +#### Debouncing + +**`debounceDelay`** (TimeSpan, default: 50ms) +- **Definition**: Minimum time delay before executing a rebalance operation after it's triggered +- **Purpose**: Prevents cache thrashing when user rapidly changes access patterns +- **Behavior**: If multiple rebalance requests occur within the debounce window, only the last one executes +- **Typical values**: 20ms to 200ms (depending on data source latency) +- **Trade-off**: Higher values reduce rebalance frequency but may delay cache optimization + +### Configuration Examples + +**Forward-heavy scrolling** (e.g., log viewer, video player): +```csharp +var options = new WindowCacheOptions( + leftCacheSize: 0.5, // Minimal backward buffer + rightCacheSize: 3.0, // Aggressive forward prefetching + leftThreshold: 0.25, + rightThreshold: 0.15 // Trigger rebalance earlier when moving forward +); +``` + +**Bidirectional navigation** (e.g., paginated data grid): +```csharp +var options = new WindowCacheOptions( + leftCacheSize: 1.5, // Balanced backward buffer + rightCacheSize: 1.5, // Balanced forward buffer + leftThreshold: 0.2, + rightThreshold: 0.2 +); +``` + +**Aggressive prefetching with stability** (e.g., high-latency data source): +```csharp +var options = new WindowCacheOptions( + leftCacheSize: 2.0, + rightCacheSize: 3.0, + leftThreshold: 0.1, // Rebalance early to maintain large buffers + rightThreshold: 0.1, + debounceDelay: TimeSpan.FromMilliseconds(100) // Wait for access pattern to stabilize +); +``` + +--- + +## 📊 Optional Diagnostics + +The cache supports optional diagnostics for monitoring behavior, measuring performance, and validating system invariants. This is useful for: +- **Testing and validation**: Verify cache behavior meets expected patterns +- **Performance monitoring**: Track cache hit/miss ratios and rebalance frequency +- **Debugging**: Understand cache lifecycle events in development +- **Production observability**: Optional instrumentation for metrics collection + +### ⚠️ CRITICAL: Exception Handling + +**You MUST handle the `RebalanceExecutionFailed` event in production applications.** + +Rebalance operations run in fire-and-forget background tasks. When exceptions occur, they are silently swallowed to prevent application crashes. Without proper handling of `RebalanceExecutionFailed`: + +- ❌ Silent failures in background operations +- ❌ Cache stops rebalancing with no indication +- ❌ Degraded performance with no diagnostics +- ❌ Data source errors go unnoticed + +**Minimum requirement: Log all failures** + +```csharp +public class LoggingCacheDiagnostics : ICacheDiagnostics +{ + private readonly ILogger _logger; + + public LoggingCacheDiagnostics(ILogger logger) + { + _logger = logger; + } + + public void RebalanceExecutionFailed(Exception ex) + { + // CRITICAL: Always log rebalance failures + _logger.LogError(ex, "Cache rebalance execution failed. Cache may not be optimally sized."); + } + + // ...implement other methods (can be no-op if you only care about failures)... +} +``` + +For production systems, consider: +- **Alerting**: Trigger alerts after N consecutive failures +- **Metrics**: Track failure rate and exception types +- **Circuit breaker**: Disable rebalancing after repeated failures +- **Structured logging**: Include cache state and requested range context + +### Using Diagnostics + +```csharp +using SlidingWindowCache.Infrastructure.Instrumentation; + +// Create diagnostics instance +var diagnostics = new EventCounterCacheDiagnostics(); + +// Pass to cache constructor +var cache = new WindowCache( + dataSource: myDataSource, + domain: new IntegerFixedStepDomain(), + options: options, + cacheDiagnostics: diagnostics // Optional parameter +); + +// Access diagnostic counters +Console.WriteLine($"Full cache hits: {diagnostics.UserRequestFullCacheHit}"); +Console.WriteLine($"Rebalances completed: {diagnostics.RebalanceExecutionCompleted}"); +``` + +### Zero-Cost Abstraction + +If no diagnostics instance is provided (default), the cache uses `NoOpDiagnostics` - a zero-overhead implementation with empty method bodies that the JIT compiler can optimize away completely. This ensures diagnostics add zero performance overhead when not used. + +**For complete metric descriptions, custom implementations, and advanced patterns, see [Diagnostics Guide](docs/diagnostics.md).** + +--- + +## 📚 Documentation + +For detailed architectural documentation, see: + +### Mathematical Foundations +- **[Intervals.NET](https://github.com/blaze6950/Intervals.NET)** - Robust interval and range handling library that underpins cache logic. See README and documentation for core concepts like `Range`, `Domain`, `RangeData`, and interval operations. + +### Core Architecture + +- **[Invariants](docs/invariants.md)** - Complete list of system invariants and guarantees +- **[Scenario Model](docs/scenario-model.md)** - Temporal behavior scenarios (User Path, Decision Path, Rebalance Execution) +- **[Actors & Responsibilities](docs/actors-and-responsibilities.md)** - System actors and invariant ownership mapping +- **[Actors to Components Mapping](docs/actors-to-components-mapping.md)** - How architectural actors map to concrete components +- **[Cache State Machine](docs/cache-state-machine.md)** - Formal state machine with mutation ownership and concurrency semantics +- **[Concurrency Model](docs/concurrency-model.md)** - Single-writer architecture and eventual consistency model + +### Implementation Details + +- **[Component Map](docs/component-map.md)** - Comprehensive component catalog with responsibilities and interactions +- **[Storage Strategies](docs/storage-strategies.md)** - Detailed comparison of Snapshot vs. CopyOnRead modes and multi-level cache patterns +- **[Diagnostics](docs/diagnostics.md)** - Optional instrumentation and observability guide + +### Testing Infrastructure + +- **[Invariant Test Suite README](tests/SlidingWindowCache.Invariants.Tests/README.md)** - Comprehensive invariant test suite with deterministic synchronization +- **[Benchmark Suite README](benchmarks/SlidingWindowCache.Benchmarks/README.md)** - BenchmarkDotNet performance benchmarks + - **RebalanceFlowBenchmarks** - Behavior-driven rebalance cost analysis (Fixed/Growing/Shrinking span patterns) + - **UserFlowBenchmarks** - User-facing API latency (Full hit, Partial hit, Full miss scenarios) + - **ScenarioBenchmarks** - End-to-end cold start performance + - **Storage Strategy Comparison** - Snapshot vs CopyOnRead allocation and performance tradeoffs across all suites +- **Deterministic Testing**: `WaitForIdleAsync()` API provides race-free synchronization with background rebalance operations for testing, graceful shutdown, health checks, and integration scenarios + +### Key Architectural Principles + +1. **Cache Contiguity**: Cache data must always remain contiguous (no gaps). Non-intersecting requests fully replace the cache. +2. **User Priority**: User requests always cancel ongoing/pending rebalance operations to maintain responsiveness. +3. **Single-Writer Architecture**: Only Rebalance Execution writes to cache state; User Path is read-only. +4. **Lock-Free Concurrency**: Intent management uses `Interlocked.Exchange` for atomic operations - no locks, no race conditions, guaranteed progress. Validated under concurrent load in test suite. + +--- + +## ⚡ Performance Considerations + +- **Snapshot mode**: O(1) reads, but O(n) rebalance with array allocation +- **CopyOnRead mode**: O(n) reads (copy cost), but cheaper rebalance operations +- **Rebalancing is asynchronous**: Does not block user reads +- **Debouncing**: Multiple rapid requests trigger only one rebalance operation +- **Diagnostics overhead**: Zero when not used (NoOpDiagnostics); minimal when enabled (~1-5ns per event) + +--- + +## 🔧 CI/CD & Package Information + +### Continuous Integration + +This project uses GitHub Actions for automated testing and deployment: + +- **Build & Test**: Runs on every push and pull request + - Compiles entire solution in Release configuration + - Executes all test suites (Unit, Integration, Invariants) with code coverage + - Validates WebAssembly compatibility via `net8.0-browser` compilation + - Uploads coverage reports to Codecov + +- **NuGet Publishing**: Automatic on main branch pushes + - Packages library with symbols and source link + - Publishes to NuGet.org with skip-duplicate + - Stores package artifacts in workflow runs + +### WebAssembly Support + +SlidingWindowCache is validated for WebAssembly compatibility: + +- **Target Framework**: `net8.0-browser` compilation validated in CI +- **Validation Project**: `SlidingWindowCache.WasmValidation` ensures all public APIs work in browser environments +- **Compatibility**: All library features available in Blazor WebAssembly and other WASM scenarios + +### NuGet Package + +**Package ID**: `SlidingWindowCache` +**Current Version**: 1.0.0 + +```bash +# Install via .NET CLI +dotnet add package SlidingWindowCache + +# Install via Package Manager +Install-Package SlidingWindowCache +``` + +**Package Contents**: +- Main library assembly (`SlidingWindowCache.dll`) +- Debug symbols (`.snupkg` for debugging) +- Source Link (GitHub source integration for "Go to Definition") +- README.md (this file) + +**Dependencies**: +- Intervals.NET.Data (>= 0.0.1) +- Intervals.NET.Domain.Default (>= 0.0.2) +- Intervals.NET.Domain.Extensions (>= 0.0.3) +- .NET 8.0 or higher + +--- + +## 🤝 Contributing & Feedback + +This project is a **personal R&D and engineering exploration** focused on cache design patterns, concurrent systems architecture, and performance optimization. While it's primarily a research endeavor, feedback and community input are highly valued and welcomed. + +### We Welcome + +- **Bug reports** - Found an issue? Please open a GitHub issue with reproduction steps +- **Feature suggestions** - Have ideas for improvements? Start a discussion or open an issue +- **Performance insights** - Benchmarked the cache in your scenario? Share your findings +- **Architecture feedback** - Thoughts on the design patterns or implementation? Let's discuss +- **Documentation improvements** - Found something unclear? Contributions to docs are appreciated +- **Positive feedback** - If the library is useful to you, that's great to know! + +### How to Contribute + +- **Issues**: Use [GitHub Issues](https://github.com/blaze6950/SlidingWindowCache/issues) for bugs, feature requests, or questions +- **Discussions**: Use [GitHub Discussions](https://github.com/blaze6950/SlidingWindowCache/discussions) for broader topics, ideas, or design conversations +- **Pull Requests**: Code contributions are welcome, but please open an issue first to discuss significant changes + +This project benefits from community feedback while maintaining a focused research direction. All constructive input helps improve the library's design, implementation, and documentation. + +--- + +## License + +MIT \ No newline at end of file diff --git a/SlidingWindowCache.sln b/SlidingWindowCache.sln new file mode 100644 index 0000000..4aa43bb --- /dev/null +++ b/SlidingWindowCache.sln @@ -0,0 +1,83 @@ +Microsoft Visual Studio Solution File, Format Version 12.00 +Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SlidingWindowCache", "src\SlidingWindowCache\SlidingWindowCache.csproj", "{40C9BEF3-8CFA-43CC-AFE0-7E374DF7F9A5}" +EndProject +Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SlidingWindowCache.WasmValidation", "src\SlidingWindowCache.WasmValidation\SlidingWindowCache.WasmValidation.csproj", "{A1B2C3D4-E5F6-4A5B-8C9D-0E1F2A3B4C5D}" +EndProject +Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "SolutionItems", "SolutionItems", "{EB667A96-0E73-48B6-ACC8-C99369A59D0D}" + ProjectSection(SolutionItems) = preProject + README.md = README.md + EndProjectSection 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Behavior-driven benchmarking suite focused exclusively on rebalance mechanics and storage rematerialization cost. +/// +/// BENCHMARK PHILOSOPHY: +/// This suite models system behavior through three orthogonal axes: +/// ✔ RequestedRange Span Behavior (Fixed/Growing/Shrinking) - models requested range span dynamics +/// ✔ Storage Strategy (Snapshot/CopyOnRead) - measures rematerialization tradeoffs +/// ✔ Base RequestedRange Span Size (100/1000/10000) - tests scaling behavior +/// +/// PERFORMANCE MODEL: +/// Rebalance cost depends primarily on: +/// ✔ Span stability/volatility (behavior axis) +/// ✔ Buffer reuse feasibility (storage axis) +/// ✔ Capacity growth patterns (size axis) +/// +/// NOT on: +/// ✖ Cache hit/miss classification (irrelevant for rebalance cost) +/// ✖ DataSource performance (isolated via SynchronousDataSource) +/// ✖ Decision logic (covered by tests, not benchmarked) +/// +/// EXECUTION MODEL: Deterministic multi-request sequence → Measure cumulative rebalance cost +/// +/// Methodology: +/// - Fresh cache per iteration +/// - Zero-latency SynchronousDataSource isolates cache mechanics +/// - Deterministic request sequence precomputed in IterationSetup (RequestsPerInvocation = 10) +/// - Each request guarantees rebalance via range shift and aggressive thresholds +/// - WaitForIdleAsync after EACH request (measuring rebalance completion) +/// - Benchmark method contains ZERO workload logic, ZERO branching, ZERO allocations +/// +/// Workload Generation: +/// - ALL span calculations occur in BuildRequestSequence() +/// - ALL branching occurs in BuildRequestSequence() +/// - Benchmark method only iterates precomputed array and awaits results +/// +/// EXPECTED BEHAVIOR: +/// - Fixed RequestedRange Span: CopyOnRead optimal (buffer reuse), Snapshot consistent (always allocates) +/// - Growing RequestedRange Span: CopyOnRead capacity growth penalty, Snapshot stable cost +/// - Shrinking RequestedRange Span: Both strategies handle well, CopyOnRead may over-allocate +/// +[MemoryDiagnoser] +[MarkdownExporter] +public class RebalanceFlowBenchmarks +{ + /// + /// RequestedRange Span behavior model: Fixed (stable), Growing (increasing), Shrinking (decreasing) + /// + public enum SpanBehavior + { + Fixed, + Growing, + Shrinking + } + + /// + /// Storage strategy: Snapshot (array-based) vs CopyOnRead (list-based) + /// + public enum StorageStrategy + { + Snapshot, + CopyOnRead + } + + // Benchmark Parameters - 3 Orthogonal Axes + + /// + /// RequestedRange Span behavior model determining how requested range span evolves across iterations + /// + [Params(SpanBehavior.Fixed, SpanBehavior.Growing, SpanBehavior.Shrinking)] + public SpanBehavior Behavior { get; set; } + + /// + /// Storage strategy for cache rematerialization + /// + [Params(StorageStrategy.Snapshot, StorageStrategy.CopyOnRead)] + public StorageStrategy Strategy { get; set; } + + /// + /// Base span size for requested ranges - tests scaling behavior from small to large data volumes + /// + [Params(100, 1_000, 10_000)] + public int BaseSpanSize { get; set; } + + // Configuration Constants + + /// + /// Cache coefficient for left/right prefetch - fixed to isolate span behavior effects + /// + private const int CacheCoefficientSize = 10; + + /// + /// Growth factor per iteration for Growing RequestedRange span behavior + /// + private const int GrowthFactor = 100; + + /// + /// Shrink factor per iteration for Shrinking RequestedRange span behavior + /// + private const int ShrinkFactor = 100; + + /// + /// Initial range start position - arbitrary but consistent across all benchmarks + /// + private const int InitialStart = 10000; + + /// + /// Number of requests executed per benchmark invocation - deterministic workload size + /// + private const int RequestsPerInvocation = 10; + + // Infrastructure + + private WindowCache? _cache; + private SynchronousDataSource _dataSource = null!; + private IntegerFixedStepDomain _domain; + private WindowCacheOptions _options = null!; + + // Deterministic Workload Storage + + /// + /// Precomputed request sequence for current iteration - generated in IterationSetup. + /// Contains EXACTLY RequestsPerInvocation ranges with all span calculations completed. + /// Benchmark methods iterate through this array without any workload logic. + /// + private Range[] _requestSequence = null!; + + [GlobalSetup] + public void GlobalSetup() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SynchronousDataSource(_domain); + + // Configure cache with aggressive thresholds to guarantee rebalancing + // leftThreshold=0, rightThreshold=0 means any request outside current window triggers rebalance + var readMode = Strategy switch + { + StorageStrategy.Snapshot => UserCacheReadMode.Snapshot, + StorageStrategy.CopyOnRead => UserCacheReadMode.CopyOnRead, + _ => throw new ArgumentOutOfRangeException(nameof(Strategy)) + }; + + _options = new WindowCacheOptions( + leftCacheSize: CacheCoefficientSize, + rightCacheSize: CacheCoefficientSize, + readMode: readMode, + leftThreshold: 1, // Set to 1 (100%) to ensure any request even the same range as previous triggers rebalance, isolating rebalance cost + rightThreshold: 0 + ); + } + + [IterationSetup] + public void IterationSetup() + { + // Create fresh cache for this iteration + _cache = new WindowCache( + _dataSource, + _domain, + _options + ); + + // Compute initial range for priming the cache + var initialRange = Intervals.NET.Factories.Range.Closed(InitialStart, InitialStart + BaseSpanSize - 1); + + // Prime cache with initial window + _cache.GetDataAsync(initialRange, CancellationToken.None).GetAwaiter().GetResult(); + _cache.WaitForIdleAsync().GetAwaiter().GetResult(); + + // Build deterministic request sequence with all workload logic + _requestSequence = BuildRequestSequence(initialRange); + } + + /// + /// Builds a deterministic request sequence based on the configured span behavior. + /// This method contains ALL workload generation logic, span calculations, and branching. + /// The benchmark method will execute this precomputed sequence with zero overhead. + /// + /// The initial primed range used to seed the sequence + /// Array of EXACTLY RequestsPerInvocation ranges, precomputed and ready to execute + private Range[] BuildRequestSequence(Range initialRange) + { + var sequence = new Range[RequestsPerInvocation]; + + for (var i = 0; i < RequestsPerInvocation; i++) + { + Range requestRange; + + switch (Behavior) + { + case SpanBehavior.Fixed: + // Fixed: Span remains constant, position shifts by +1 each request + requestRange = initialRange.Shift(_domain, i + 1); + break; + + case SpanBehavior.Growing: + // Growing: Span increases deterministically, position shifts slightly + var spanGrow = i * GrowthFactor; + requestRange = initialRange.Shift(_domain, i + 1).Expand(_domain, 0, spanGrow); + break; + + case SpanBehavior.Shrinking: + // Shrinking: Span decreases deterministically, respecting minimum + var spanShrink = i * ShrinkFactor; + var bigInitialRange = initialRange.Expand(_domain, 0, RequestsPerInvocation * ShrinkFactor); // Ensure we have room to shrink + requestRange = bigInitialRange.Shift(_domain, i + 1).Expand(_domain, 0, -spanShrink); + break; + + default: + throw new ArgumentOutOfRangeException(nameof(Behavior), Behavior, "Unsupported span behavior"); + } + + sequence[i] = requestRange; + } + + return sequence; + } + + [IterationCleanup] + public void IterationCleanup() + { + // Ensure cache is idle before next iteration + _cache?.WaitForIdleAsync(TimeSpan.FromSeconds(5)).GetAwaiter().GetResult(); + } + + /// + /// Measures rebalance rematerialization cost for the configured span behavior and storage strategy. + /// Executes a deterministic sequence of requests, each followed by rebalance completion. + /// This benchmark measures ONLY the rebalance path - decision logic is excluded. + /// Contains ZERO workload logic, ZERO branching, ZERO span calculations. + /// + [Benchmark] + public async Task Rebalance() + { + // Execute precomputed request sequence + // Each request triggers rebalance (guaranteed by leftThreshold=1 and range shift) + // Measure complete rebalance cycle for each request + foreach (var requestRange in _requestSequence) + { + await _cache!.GetDataAsync(requestRange, CancellationToken.None); + + // Explicitly measure rebalance cycle completion + // This captures the rematerialization cost we're benchmarking + await _cache.WaitForIdleAsync(timeout: TimeSpan.FromSeconds(10)); + } + } +} diff --git a/benchmarks/SlidingWindowCache.Benchmarks/Benchmarks/ScenarioBenchmarks.cs b/benchmarks/SlidingWindowCache.Benchmarks/Benchmarks/ScenarioBenchmarks.cs new file mode 100644 index 0000000..bf1cc26 --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/Benchmarks/ScenarioBenchmarks.cs @@ -0,0 +1,120 @@ +using BenchmarkDotNet.Attributes; +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using SlidingWindowCache.Benchmarks.Infrastructure; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Benchmarks.Benchmarks; + +/// +/// Scenario Benchmarks +/// End-to-end scenario testing including cold start and locality patterns. +/// NOT microbenchmarks - measures complete workflows. +/// +/// EXECUTION FLOW: Simulates realistic usage patterns +/// +/// Methodology: +/// - Fresh cache per iteration +/// - Cold start: Measures initial cache population (includes WaitForIdleAsync) +/// - Compares cached vs uncached approaches +/// +[MemoryDiagnoser] +[MarkdownExporter] +[GroupBenchmarksBy(BenchmarkDotNet.Configs.BenchmarkLogicalGroupRule.ByCategory)] +public class ScenarioBenchmarks +{ + private SynchronousDataSource _dataSource = null!; + private IntegerFixedStepDomain _domain; + private WindowCache? _snapshotCache; + private WindowCache? _copyOnReadCache; + private WindowCacheOptions _snapshotOptions = null!; + private WindowCacheOptions _copyOnReadOptions = null!; + private Range _coldStartRange; + + /// + /// Requested range size - varies from small (100) to large (10,000) to test scenario scaling behavior. + /// + [Params(100, 1_000, 10_000)] + public int RangeSpan { get; set; } + + /// + /// Cache coefficient size for left/right prefetch - varies from minimal (1) to aggressive (100). + /// Combined with RangeSpan, determines total materialized cache size in scenarios. + /// + [Params(1, 10, 100)] + public int CacheCoefficientSize { get; set; } + + private int ColdStartRangeStart => 10000; + private int ColdStartRangeEnd => ColdStartRangeStart + RangeSpan - 1; + + [GlobalSetup] + public void GlobalSetup() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SynchronousDataSource(_domain); + + // Cold start configuration + _coldStartRange = Intervals.NET.Factories.Range.Closed( + ColdStartRangeStart, + ColdStartRangeEnd + ); + + _snapshotOptions = new WindowCacheOptions( + leftCacheSize: CacheCoefficientSize, + rightCacheSize: CacheCoefficientSize, + UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2 + ); + + _copyOnReadOptions = new WindowCacheOptions( + leftCacheSize: CacheCoefficientSize, + rightCacheSize: CacheCoefficientSize, + UserCacheReadMode.CopyOnRead, + leftThreshold: 0.2, + rightThreshold: 0.2 + ); + } + + #region Cold Start Benchmarks + + [IterationSetup(Target = nameof(ColdStart_Rebalance_Snapshot) + "," + nameof(ColdStart_Rebalance_CopyOnRead))] + public void ColdStartIterationSetup() + { + // Create fresh caches for cold start measurement + _snapshotCache = new WindowCache( + _dataSource, + _domain, + _snapshotOptions + ); + + _copyOnReadCache = new WindowCache( + _dataSource, + _domain, + _copyOnReadOptions + ); + } + + [Benchmark(Baseline = true)] + [BenchmarkCategory("ColdStart")] + public async Task ColdStart_Rebalance_Snapshot() + { + // Measure complete cold start: initial fetch + rebalance + // WaitForIdleAsync is PART of cold start cost + await _snapshotCache!.GetDataAsync(_coldStartRange, CancellationToken.None); + await _snapshotCache.WaitForIdleAsync(timeout: TimeSpan.FromSeconds(5)); + } + + [Benchmark] + [BenchmarkCategory("ColdStart")] + public async Task ColdStart_Rebalance_CopyOnRead() + { + // Measure complete cold start: initial fetch + rebalance + // WaitForIdleAsync is PART of cold start cost + await _copyOnReadCache!.GetDataAsync(_coldStartRange, CancellationToken.None); + await _copyOnReadCache.WaitForIdleAsync(timeout: TimeSpan.FromSeconds(5)); + } + + #endregion +} diff --git a/benchmarks/SlidingWindowCache.Benchmarks/Benchmarks/UserFlowBenchmarks.cs b/benchmarks/SlidingWindowCache.Benchmarks/Benchmarks/UserFlowBenchmarks.cs new file mode 100644 index 0000000..f2b63a2 --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/Benchmarks/UserFlowBenchmarks.cs @@ -0,0 +1,228 @@ +using BenchmarkDotNet.Attributes; +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using Intervals.NET.Domain.Extensions.Fixed; +using SlidingWindowCache.Benchmarks.Infrastructure; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Benchmarks.Benchmarks; + +/// +/// User Request Flow Benchmarks +/// Measures ONLY user-facing request latency/cost. +/// Rebalance/background activity is EXCLUDED from measurements via cleanup phase. +/// +/// EXECUTION FLOW: User Request → Measures direct API call cost +/// +/// Methodology: +/// - Fresh cache per iteration +/// - Benchmark methods measure ONLY GetDataAsync cost +/// - Rebalance triggered by mutations, but NOT included in measurement +/// - WaitForIdleAsync moved to [IterationCleanup] +/// - Deterministic overlap patterns (no randomness) +/// +[MemoryDiagnoser] +[MarkdownExporter] +[GroupBenchmarksBy(BenchmarkDotNet.Configs.BenchmarkLogicalGroupRule.ByCategory)] +public class UserFlowBenchmarks +{ + private WindowCache? _snapshotCache; + private WindowCache? _copyOnReadCache; + private SynchronousDataSource _dataSource = null!; + private IntegerFixedStepDomain _domain; + + /// + /// Requested range size - varies from small (100) to large (10,000) to test scaling behavior. + /// + [Params(100, 1_000, 10_000)] + public int RangeSpan { get; set; } + + /// + /// Cache coefficient size for left/right prefetch - varies from minimal (1) to aggressive (100). + /// Combined with RangeSpan, determines total materialized cache size. + /// + [Params(1, 10, 100)] + public int CacheCoefficientSize { get; set; } + + // Range will be calculated based on RangeSpan parameter + private int CachedStart => 10000; + private int CachedEnd => CachedStart + RangeSpan; + + private Range InitialCacheRange => + Intervals.NET.Factories.Range.Closed(CachedStart, CachedEnd); + + private Range InitialCacheRangeAfterRebalance => InitialCacheRange + .ExpandByRatio(_domain, CacheCoefficientSize, CacheCoefficientSize); + + private Range FullHitRange => InitialCacheRangeAfterRebalance + .ExpandByRatio(_domain, -0.2, -0.2); // 20% inside cached window + + private Range FullMissRange => InitialCacheRangeAfterRebalance + .Shift(_domain, InitialCacheRangeAfterRebalance.Span(_domain).Value * 3); // Shift far outside cached window + + private Range PartialHitForwardRange => InitialCacheRangeAfterRebalance + .Shift(_domain, InitialCacheRangeAfterRebalance.Span(_domain).Value / 2); // Shift forward by 50% of cached span + + private Range PartialHitBackwardRange => InitialCacheRangeAfterRebalance + .Shift(_domain, -InitialCacheRangeAfterRebalance.Span(_domain).Value / 2); // Shift backward by 50% of cached + + // Pre-calculated ranges + private Range _fullHitRange; + private Range _partialHitForwardRange; + private Range _partialHitBackwardRange; + private Range _fullMissRange; + + private WindowCacheOptions _snapshotOptions; + private WindowCacheOptions _copyOnReadOptions; + + [GlobalSetup] + public void GlobalSetup() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SynchronousDataSource(_domain); + + // Pre-calculate all deterministic ranges + // Full hit: request entirely within cached window + _fullHitRange = FullHitRange; + + // Partial hit forward + _partialHitForwardRange = PartialHitForwardRange; + + // Partial hit backward + _partialHitBackwardRange = PartialHitBackwardRange; + + // Full miss: no overlap with cached window + _fullMissRange = FullMissRange; + + // Configure cache options + _snapshotOptions = new WindowCacheOptions( + leftCacheSize: CacheCoefficientSize, + rightCacheSize: CacheCoefficientSize, + UserCacheReadMode.Snapshot, + leftThreshold: 0, + rightThreshold: 0 + ); + + _copyOnReadOptions = new WindowCacheOptions( + leftCacheSize: CacheCoefficientSize, + rightCacheSize: CacheCoefficientSize, + UserCacheReadMode.CopyOnRead, + leftThreshold: 0, + rightThreshold: 0 + ); + } + + [IterationSetup] + public void IterationSetup() + { + // Create fresh caches for each iteration - no state drift + _snapshotCache = new WindowCache( + _dataSource, + _domain, + _snapshotOptions + ); + + _copyOnReadCache = new WindowCache( + _dataSource, + _domain, + _copyOnReadOptions + ); + + // Prime both caches with known initial window + var initialRange = Intervals.NET.Factories.Range.Closed(CachedStart, CachedEnd); + _snapshotCache.GetDataAsync(initialRange, CancellationToken.None).GetAwaiter().GetResult(); + _copyOnReadCache.GetDataAsync(initialRange, CancellationToken.None).GetAwaiter().GetResult(); + + // Wait for idle state - deterministic starting point + _snapshotCache.WaitForIdleAsync().GetAwaiter().GetResult(); + _copyOnReadCache.WaitForIdleAsync().GetAwaiter().GetResult(); + } + + [IterationCleanup] + public void IterationCleanup() + { + // Wait for any triggered rebalance to complete + // This ensures measurements are NOT contaminated by background activity + _snapshotCache?.WaitForIdleAsync(timeout: TimeSpan.FromSeconds(5)).GetAwaiter().GetResult(); + _copyOnReadCache?.WaitForIdleAsync(timeout: TimeSpan.FromSeconds(5)).GetAwaiter().GetResult(); + } + + #region Full Hit Benchmarks + + [Benchmark(Baseline = true)] + [BenchmarkCategory("FullHit")] + public async Task> User_FullHit_Snapshot() + { + // No rebalance triggered + return await _snapshotCache!.GetDataAsync(_fullHitRange, CancellationToken.None); + } + + [Benchmark] + [BenchmarkCategory("FullHit")] + public async Task> User_FullHit_CopyOnRead() + { + // No rebalance triggered + return await _copyOnReadCache!.GetDataAsync(_fullHitRange, CancellationToken.None); + } + + #endregion + + #region Partial Hit Benchmarks + + [Benchmark] + [BenchmarkCategory("PartialHit")] + public async Task> User_PartialHit_ForwardShift_Snapshot() + { + // Rebalance triggered, handled in cleanup + return await _snapshotCache!.GetDataAsync(_partialHitForwardRange, CancellationToken.None); + } + + [Benchmark] + [BenchmarkCategory("PartialHit")] + public async Task> User_PartialHit_ForwardShift_CopyOnRead() + { + // Rebalance triggered, handled in cleanup + return await _copyOnReadCache!.GetDataAsync(_partialHitForwardRange, CancellationToken.None); + } + + [Benchmark] + [BenchmarkCategory("PartialHit")] + public async Task> User_PartialHit_BackwardShift_Snapshot() + { + // Rebalance triggered, handled in cleanup + return await _snapshotCache!.GetDataAsync(_partialHitBackwardRange, CancellationToken.None); + } + + [Benchmark] + [BenchmarkCategory("PartialHit")] + public async Task> User_PartialHit_BackwardShift_CopyOnRead() + { + // Rebalance triggered, handled in cleanup + return await _copyOnReadCache!.GetDataAsync(_partialHitBackwardRange, CancellationToken.None); + } + + #endregion + + #region Full Miss Benchmarks + + [Benchmark] + [BenchmarkCategory("FullMiss")] + public async Task> User_FullMiss_Snapshot() + { + // No overlap - full cache replacement + // Rebalance triggered, handled in cleanup + return await _snapshotCache!.GetDataAsync(_fullMissRange, CancellationToken.None); + } + + [Benchmark] + [BenchmarkCategory("FullMiss")] + public async Task> User_FullMiss_CopyOnRead() + { + // No overlap - full cache replacement + // Rebalance triggered, handled in cleanup + return await _copyOnReadCache!.GetDataAsync(_fullMissRange, CancellationToken.None); + } + + #endregion +} \ No newline at end of file diff --git a/benchmarks/SlidingWindowCache.Benchmarks/Infrastructure/SynchronousDataSource.cs b/benchmarks/SlidingWindowCache.Benchmarks/Infrastructure/SynchronousDataSource.cs new file mode 100644 index 0000000..39f8b5d --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/Infrastructure/SynchronousDataSource.cs @@ -0,0 +1,61 @@ +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using Intervals.NET.Domain.Extensions.Fixed; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Dto; + +namespace SlidingWindowCache.Benchmarks.Infrastructure; + +/// +/// Zero-latency synchronous IDataSource for isolating rebalance and cache mutation costs. +/// Returns data immediately without Task.Delay or I/O simulation. +/// Designed for RebalanceCostBenchmarks to measure pure cache mechanics without data source interference. +/// +public sealed class SynchronousDataSource : IDataSource +{ + private readonly IntegerFixedStepDomain _domain; + + public SynchronousDataSource(IntegerFixedStepDomain domain) + { + _domain = domain; + } + + /// + /// Fetches data for a single range with zero latency. + /// Data generation: Returns the integer value at each position in the range. + /// + public Task> FetchAsync(Range range, CancellationToken cancellationToken) => + Task.FromResult(GenerateDataForRange(range)); + + /// + /// Fetches data for multiple ranges with zero latency. + /// + public Task>> FetchAsync( + IEnumerable> ranges, + CancellationToken cancellationToken) + { + // Synchronous generation for all chunks + var chunks = ranges.Select(range => new RangeChunk( + range, + GenerateDataForRange(range) + )); + + return Task.FromResult(chunks); + } + + /// + /// Generates deterministic data for a range. + /// Each position i in the range produces value i. + /// + private IEnumerable GenerateDataForRange(Range range) + { + var start = range.Start.Value; + var count = (int)range.Span(_domain).Value; + + for (var i = 0; i < count; i++) + { + yield return start + i; + } + } + +} \ No newline at end of file diff --git a/benchmarks/SlidingWindowCache.Benchmarks/Program.cs b/benchmarks/SlidingWindowCache.Benchmarks/Program.cs new file mode 100644 index 0000000..5e4ca39 --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/Program.cs @@ -0,0 +1,18 @@ +using BenchmarkDotNet.Running; + +namespace SlidingWindowCache.Benchmarks; + +/// +/// BenchmarkDotNet runner for SlidingWindowCache performance benchmarks. +/// +public class Program +{ + public static void Main(string[] args) + { + // Run all benchmark classes + var summary = BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args); + + // Alternative: Run specific benchmark + // var summary = BenchmarkRunner.Run(); + } +} \ No newline at end of file diff --git a/benchmarks/SlidingWindowCache.Benchmarks/README.md b/benchmarks/SlidingWindowCache.Benchmarks/README.md new file mode 100644 index 0000000..877df05 --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/README.md @@ -0,0 +1,522 @@ +# SlidingWindowCache Benchmarks + +Comprehensive BenchmarkDotNet performance suite for SlidingWindowCache, measuring architectural performance characteristics using **public API only**. + +**🎯 Methodologically Correct Benchmarks**: This suite follows rigorous benchmark methodology to ensure deterministic, reliable, and interpretable results. + +--- + +## Overview + +This benchmark project provides reliable, deterministic performance measurements organized around **two distinct execution flows** of SlidingWindowCache: + +### Execution Flow Model + +SlidingWindowCache has **two independent cost centers**: + +1. **User Request Flow** → Measures latency/cost of user-facing API calls + - Rebalance/background activity is **NOT** included in measured results + - Focus: Direct `GetDataAsync` call overhead + +2. **Rebalance/Maintenance Flow** → Measures cost of window maintenance operations + - Explicitly waits for stabilization using `WaitForIdleAsync` + - Focus: Background window management and cache mutation costs + +### What We Measure + +- **Snapshot vs CopyOnRead** storage modes across both flows +- **User Request Flow**: Full hit, partial hit, full miss scenarios +- **Rebalance Flow**: Maintenance costs after partial hit and full miss +- **Scenario Testing**: Cold start performance and sequential locality advantages +- **Scaling Behavior**: Performance across varying data volumes and cache sizes + +--- + +## Parameterization Strategy + +Benchmarks are **parameterized** to measure scaling behavior across different workload characteristics. The parameter strategy differs by benchmark suite to target specific performance aspects: + +### User Flow & Scenario Benchmarks Parameters + +These benchmarks use a 2-axis parameter matrix to explore cache sizing tradeoffs: + +1. **`RangeSpan`** - Requested range size + - Values: `[100, 1_000, 10_000]` + - Purpose: Test how storage strategies scale with data volume + - Range: Small to large data volumes + +2. **`CacheCoefficientSize`** - Left/right prefetch multipliers + - Values: `[1, 10, 100]` + - Purpose: Test rebalance cost vs cache size tradeoff + - Total cache size = `RangeSpan × (1 + leftCoeff + rightCoeff)` + +**Parameter Matrix**: 3 range sizes × 3 cache coefficients = **9 parameter combinations per benchmark method** + +### Rebalance Flow Benchmarks Parameters + +These benchmarks use a 3-axis orthogonal design to isolate rebalance behavior: + +1. **`Behavior`** - Range span evolution pattern + - Values: `[Fixed, Growing, Shrinking]` + - Purpose: Models how requested range span changes over time + - Fixed: Constant span, position shifts + - Growing: Span increases each iteration + - Shrinking: Span decreases each iteration + +2. **`Strategy`** - Storage rematerialization approach + - Values: `[Snapshot, CopyOnRead]` + - Purpose: Compare array-based vs list-based storage under different dynamics + +3. **`BaseSpanSize`** - Initial requested range size + - Values: `[100, 1_000, 10_000]` + - Purpose: Test scaling behavior from small to large data volumes + +**Parameter Matrix**: 3 behaviors × 2 strategies × 3 sizes = **18 parameter combinations** + +### Expected Scaling Insights + +**Snapshot Mode:** +- ✅ **Advantage at small-to-medium sizes** (RangeSpan < 10,000) + - Zero-allocation reads dominate + - Rebalance cost acceptable +- ⚠️ **LOH pressure at large sizes** (RangeSpan ≥ 10,000) + - Array allocations go to LOH (no compaction) + - GC pressure increases with Gen2 collections visible +- 📊 **Observed**: ~224KB allocation for Fixed/Snapshot at BaseSpanSize=100 vs ~92KB for CopyOnRead + +**CopyOnRead Mode:** +- ❌ **Disadvantage at small sizes** (RangeSpan < 1,000) + - Per-read allocation overhead visible + - List overhead not amortized +- ✅ **Competitive at medium-to-large sizes** (RangeSpan ≥ 1,000) + - List growth amortizes allocation cost + - Reduced LOH pressure +- ✅ **Consistent allocation advantage** + - 2-3x lower allocations across most scenarios + - Buffer reuse shows in steady-state operations +- 📊 **Observed**: Allocation differences scale with BaseSpanSize (e.g., ~2.5MB vs ~16MB at BaseSpanSize=10,000) + +### Interpretation Guide + +When analyzing results, look for: + +1. **Allocation patterns**: + - Snapshot: Zero on read, large on rebalance + - CopyOnRead: Constant on read, incremental on rebalance + - **Actual measurements show 2-3x allocation reduction for CopyOnRead** + +2. **Memory usage trends**: + - Watch for Gen2 collections (LOH pressure indicator at BaseSpanSize=10,000) + - Compare total allocated bytes across modes + - CopyOnRead consistently shows lower memory footprint + +3. **Execution time patterns**: + - **Rebalance benchmarks cluster around ~1 second baseline** across all parameters + - This isolation reveals pure rebalance cost without I/O variance + - User flow benchmarks show microsecond-level latencies for cache hits + - Cold start scenarios show ~97-98ms for initial population + +4. **Behavior-driven insights (RebalanceFlowBenchmarks)**: + - Fixed span: Predictable, stable costs + - Growing span: Storage strategy differences become visible + - Shrinking span: Both strategies handle gracefully + - CopyOnRead shows more stable allocation patterns across behaviors + +--- + +## Design Principles + +### 1. Public API Only +- ✅ No internal types +- ✅ No reflection +- ✅ Only uses public `WindowCache` API + +### 2. Deterministic Behavior +- ✅ `FakeDataSource` with no randomness +- ✅ `SynchronousDataSource` for zero-latency isolation +- ✅ Stable, predictable data generation +- ✅ Configurable simulated latency +- ✅ No I/O operations + +### 3. Methodological Rigor +- ✅ **No state reuse**: Fresh cache per iteration via `[IterationSetup]` +- ✅ **Explicit rebalance handling**: `WaitForIdleAsync` in setup/cleanup, NOT in benchmark methods +- ✅ **Clear separation**: Read microbenchmarks vs partial-hit vs scenario-level +- ✅ **Isolation**: Each benchmark measures ONE thing +- ✅ **MemoryDiagnoser** for allocation tracking +- ✅ **MarkdownExporter** for report generation +- ✅ **Parameterization**: Comprehensive scaling analysis + +--- + +## Benchmark Categories + +Benchmarks are organized by **execution flow** to clearly separate user-facing costs from background maintenance costs. + +### 📱 User Request Flow Benchmarks + +**File**: `UserFlowBenchmarks.cs` + +**Goal**: Measure ONLY user-facing request latency. Rebalance/background activity is EXCLUDED from measurements. + +**Parameters**: `RangeSpan` × `CacheCoefficientSize` = **9 combinations** +- RangeSpan: `[100, 1_000, 10_000]` +- CacheCoefficientSize: `[1, 10, 100]` + +**Contract**: +- Benchmark methods measure ONLY `GetDataAsync` cost +- `WaitForIdleAsync` moved to `[IterationCleanup]` +- Fresh cache per iteration +- Deterministic overlap patterns (no randomness) + +**Benchmark Methods** (grouped by category): + +| Category | Method | Purpose | +|----------|--------|---------| +| **FullHit** | `User_FullHit_Snapshot` | Baseline: Full cache hit with Snapshot mode | +| **FullHit** | `User_FullHit_CopyOnRead` | Full cache hit with CopyOnRead mode | +| **PartialHit** | `User_PartialHit_ForwardShift_Snapshot` | Partial hit moving right (Snapshot) | +| **PartialHit** | `User_PartialHit_ForwardShift_CopyOnRead` | Partial hit moving right (CopyOnRead) | +| **PartialHit** | `User_PartialHit_BackwardShift_Snapshot` | Partial hit moving left (Snapshot) | +| **PartialHit** | `User_PartialHit_BackwardShift_CopyOnRead` | Partial hit moving left (CopyOnRead) | +| **FullMiss** | `User_FullMiss_Snapshot` | Full cache miss (Snapshot) | +| **FullMiss** | `User_FullMiss_CopyOnRead` | Full cache miss (CopyOnRead) | + +**Expected Results**: +- Full hit: Snapshot ~25-30µs (minimal allocation), CopyOnRead scales with cache size +- Partial hit: Both modes serve request immediately, rebalance deferred to cleanup +- Full miss: Request served from data source, rebalance deferred to cleanup +- **Scaling**: CopyOnRead allocation grows linearly with `CacheCoefficientSize` + +--- + +### ⚙️ Rebalance Flow Benchmarks + +**File**: `RebalanceFlowBenchmarks.cs` + +**Goal**: Measure rebalance mechanics and storage rematerialization cost through behavior-driven modeling. This suite isolates how storage strategies handle different range span evolution patterns. + +**Philosophy**: Models system behavior through three orthogonal axes: +- ✔ **Span Behavior** (Fixed/Growing/Shrinking) - How requested range span evolves +- ✔ **Storage Strategy** (Snapshot/CopyOnRead) - Rematerialization approach +- ✔ **Base Span Size** (100/1,000/10,000) - Scaling behavior + +**Parameters**: `Behavior` × `Strategy` × `BaseSpanSize` = **18 combinations** +- Behavior: `[Fixed, Growing, Shrinking]` +- Strategy: `[Snapshot, CopyOnRead]` +- BaseSpanSize: `[100, 1_000, 10_000]` + +**Contract**: +- Uses `SynchronousDataSource` (zero latency) to isolate cache mechanics from I/O +- `WaitForIdleAsync` INSIDE benchmark methods (measuring rebalance completion) +- Deterministic request sequence generated in `IterationSetup` +- Each request triggers rebalance via aggressive thresholds +- Executes 10 requests per invocation, measuring cumulative rebalance cost + +**Benchmark Method**: + +| Method | Purpose | +|--------|---------| +| `Rebalance` | Measures complete rebalance cycle cost for the configured span behavior and storage strategy | + +**Span Behaviors Explained**: +- **Fixed**: Span remains constant, position shifts by +1 each request (models stable sliding window) +- **Growing**: Span increases by 100 elements per request (models expanding data requirements) +- **Shrinking**: Span decreases by 100 elements per request (models contracting data requirements) + +**Expected Results**: +- **Execution time**: Clusters around ~1.05-1.07 seconds across all parameters + - Baseline dominated by 10 × 100ms `SynchronousDataSource` delay (1 second) + - Pure rebalance overhead is ~50-70ms cumulative +- **Allocation patterns**: + - Fixed/Snapshot: ~224KB (BaseSpanSize=100) → ~16MB (BaseSpanSize=10,000) + - Fixed/CopyOnRead: ~92KB (BaseSpanSize=100) → ~2.5MB (BaseSpanSize=10,000) + - **CopyOnRead shows 2-3x allocation reduction** through buffer reuse +- **GC pressure**: Gen2 collections visible at BaseSpanSize=10,000 for Snapshot mode +- **Behavior impact**: Growing span slightly increases allocation for CopyOnRead (~560KB vs ~92KB at BaseSpanSize=100) + +--- + +### 🌍 Scenario Benchmarks (End-to-End) + +**File**: `ScenarioBenchmarks.cs` + +**Goal**: End-to-end scenario testing focusing on cold start performance. NOT microbenchmarks - measures complete workflows. + +**Parameters**: `RangeSpan` × `CacheCoefficientSize` = **9 combinations** +- RangeSpan: `[100, 1_000, 10_000]` +- CacheCoefficientSize: `[1, 10, 100]` + +**Contract**: +- Fresh cache per iteration +- Cold start: Measures complete initialization including rebalance +- `WaitForIdleAsync` is PART of the measured cold start cost + +**Benchmark Methods** (grouped by category): + +| Category | Method | Purpose | +|----------|---------|---------| +| **ColdStart** | `ColdStart_Rebalance_Snapshot` | Baseline: Initial cache population (Snapshot) | +| **ColdStart** | `ColdStart_Rebalance_CopyOnRead` | Initial cache population (CopyOnRead) | + +**Expected Results**: +- Cold start: ~97-98ms for initial population (dominated by 100ms `SynchronousDataSource` delay) +- Allocation patterns differ between modes: + - Snapshot: Single upfront array allocation + - CopyOnRead: List-based incremental allocation, less memory spike +- **Scaling**: Both modes show similar execution time (~97-150ms) +- **Memory differences**: + - Small ranges (RangeSpan=100, CacheCoefficientSize=1): Minimal difference (~7KB vs ~9KB) + - Large ranges (RangeSpan=10,000, CacheCoefficientSize=100): Snapshot ~15.8MB, CopyOnRead ~16.5MB + - CopyOnRead allocation ratio: 1.04-1.72x depending on cache size +- **GC impact**: Gen2 collections visible at largest parameter combination + +--- + +## Running Benchmarks + +### Quick Start + +```bash +# Run all benchmarks (WARNING: This will take 2-4 hours with current parameterization) +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks + +# Run specific benchmark class +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*UserFlowBenchmarks*" +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*RebalanceFlowBenchmarks*" +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*ScenarioBenchmarks*" +``` + +### Filtering Options + +```bash +# Run only FullHit category (UserFlowBenchmarks) +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*FullHit*" + +# Run only Rebalance benchmarks +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*RebalanceFlowBenchmarks*" + +# Run specific method +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*User_FullHit_Snapshot*" + +# Run specific parameter combination (e.g., BaseSpanSize=1000) +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*" -- --filter "*BaseSpanSize_1000*" +``` + +### Managing Execution Time + +With parameterization, total execution time can be significant: + +**Default configuration:** +- UserFlowBenchmarks: 9 parameters × 8 methods = 72 benchmarks +- RebalanceFlowBenchmarks: 18 parameters × 1 method = 18 benchmarks +- ScenarioBenchmarks: 9 parameters × 2 methods = 18 benchmarks +- **Total: ~108 individual benchmarks** +- **Estimated time: 2-4 hours** (depending on hardware) + +**Faster turnaround options:** + +1. **Use SimpleJob for development:** +```csharp +[SimpleJob(warmupCount: 3, iterationCount: 5)] // Add to class attributes +``` + +2. **Run subset of parameters:** +```bash +# Comment out larger parameter values in code temporarily +[Params(100, 1_000)] // Instead of all 3 values +``` + +3. **Run by category:** +```bash +# Focus on one flow at a time +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*FullHit*" +``` + +4. **Run single benchmark class:** +```bash +# Test specific aspect +dotnet run -c Release --project benchmarks/SlidingWindowCache.Benchmarks --filter "*ScenarioBenchmarks*" +``` + +--- + +## Data Sources + +### SynchronousDataSource +Zero-latency synchronous data source for isolating cache mechanics: + +```csharp +// Zero latency - isolates rebalance cost from I/O +var dataSource = new SynchronousDataSource(domain); +``` + +**Purpose**: +- Used in all benchmarks for deterministic, reproducible results +- Returns synchronous `IEnumerable` wrapped in completed `Task` +- No `Task.Delay` or async overhead +- Measures pure cache mechanics without I/O interference + +**Data Generation**: +- Deterministic: Position `i` produces value `i` +- No randomness +- Stable across runs +- Predictable memory footprint + +--- + +## Running Benchmarks + +### Run All Benchmarks +```bash +cd tests/SlidingWindowCache.Benchmarks +dotnet run -c Release +``` + +### Run Specific Benchmark Class +```bash +# User request flow benchmarks +dotnet run -c Release -- --filter *UserFlowBenchmarks* + +# Rebalance/maintenance flow benchmarks +dotnet run -c Release -- --filter *RebalanceFlowBenchmarks* + +# Scenario benchmarks (cold start + locality) +dotnet run -c Release -- --filter *ScenarioBenchmarks* +``` + +### Run Specific Method +```bash +# User flow examples +dotnet run -c Release -- --filter *User_FullHit* +dotnet run -c Release -- --filter *User_PartialHit* + +# Rebalance flow examples +dotnet run -c Release -- --filter *Rebalance_AfterPartialHit* + +# Scenario examples +dotnet run -c Release -- --filter *ColdStart_Rebalance* +dotnet run -c Release -- --filter *User_LocalityScenario* +``` + +--- + +## Interpreting Results + +### Mean Execution Time +- Lower is better +- Compare Snapshot vs CopyOnRead for same scenario +- Look for order-of-magnitude differences + +### Allocations +- **Snapshot mode**: Watch for large array allocations during rebalance +- **CopyOnRead mode**: Watch for per-read allocations +- **Gen 0/1/2**: Track garbage collection pressure + +### Memory Diagnostics +- **Allocated**: Total bytes allocated +- **Gen 0/1/2 Collections**: GC pressure indicator +- **LOH**: Large Object Heap allocations (arrays ≥85KB) + +--- + +## Methodological Guarantees + +### ✅ No State Drift +Every iteration starts from a clean, deterministic cache state via `[IterationSetup]`. + +### ✅ Explicit Rebalance Handling +- Benchmarks that trigger rebalance use `[IterationCleanup]` to wait for completion +- NO `WaitForIdleAsync` inside benchmark methods (would contaminate measurements) +- Setup phases use `WaitForIdleAsync` to ensure deterministic starting state + +### ✅ Clear Separation +- **Read microbenchmarks**: Rebalance disabled, measure read path only +- **Partial hit benchmarks**: Rebalance enabled, deterministic overlap, cleanup handles rebalance +- **Scenario benchmarks**: Full sequential patterns, cleanup handles stabilization + +### ✅ Isolation +- `RebalanceCostBenchmarks` uses `SynchronousDataSource` to isolate cache mechanics from I/O +- Each benchmark measures ONE architectural characteristic + +--- + +## Expected Performance Characteristics + +### Snapshot Mode +- ✅ **Best for**: Read-heavy workloads (high read:rebalance ratio) +- ✅ **Strengths**: Zero-allocation reads, fastest read performance +- ❌ **Weaknesses**: Expensive rebalancing, LOH pressure + +### CopyOnRead Mode +- ✅ **Best for**: Write-heavy workloads (frequent rebalancing) +- ✅ **Strengths**: Cheap rebalancing, reduced LOH pressure +- ❌ **Weaknesses**: Allocates on every read, slower read performance + +### Sequential Locality +- ✅ **Cache advantage**: Reduces data source calls by 70-80% +- ✅ **Prefetching benefit**: Most requests served from cache +- ✅ **Latency hiding**: Background rebalancing doesn't block reads + +--- + +## Architecture Goals + +These benchmarks validate: +1. **User request flow isolation** - User-facing latency measured without rebalance contamination (`UserFlowBenchmarks`) +2. **Behavior-driven rebalance analysis** - How storage strategies handle Fixed/Growing/Shrinking span dynamics (`RebalanceFlowBenchmarks`) +3. **Storage strategy tradeoffs** - Snapshot vs CopyOnRead across all workload patterns with measured allocation differences +4. **Cold start characteristics** - Complete initialization cost including first rebalance (`ScenarioBenchmarks`) +5. **Memory pressure patterns** - Allocations, GC pressure, LOH impact across parameter ranges +6. **Scaling behavior** - Performance characteristics from small (100) to large (10,000) data volumes +7. **Deterministic reproducibility** - Zero-latency `SynchronousDataSource` isolates cache mechanics from I/O variance + +--- + +## Output Files + +After running benchmarks, results are generated in two locations: + +### Results Directory (Committed to Repository) +``` +benchmarks/SlidingWindowCache.Benchmarks/Results/ +├── SlidingWindowCache.Benchmarks.Benchmarks.UserFlowBenchmarks-report-github.md +├── SlidingWindowCache.Benchmarks.Benchmarks.RebalanceFlowBenchmarks-report-github.md +└── SlidingWindowCache.Benchmarks.Benchmarks.ScenarioBenchmarks-report-github.md +``` + +These markdown reports are checked into version control for: +- Performance regression tracking +- Historical comparison +- Documentation of expected performance characteristics + +### BenchmarkDotNet Artifacts (Local Only) +``` +BenchmarkDotNet.Artifacts/ +├── results/ +│ ├── *.html (HTML reports) +│ ├── *.md (Markdown reports) +│ └── *.csv (Raw data) +└── logs/ + └── ... (detailed execution logs) +``` + +These files are generated locally and excluded from version control (`.gitignore`). + +--- + +## CI/CD Integration + +These benchmarks can be integrated into CI/CD for: +- **Performance regression detection** +- **Release performance validation** +- **Architectural decision documentation** +- **Historical performance tracking** + +Example: Run on every release and commit results to repository. + +--- + +## License + +MIT (same as parent project) diff --git a/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.RebalanceFlowBenchmarks-report-github.md b/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.RebalanceFlowBenchmarks-report-github.md new file mode 100644 index 0000000..e114e74 --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.RebalanceFlowBenchmarks-report-github.md @@ -0,0 +1,31 @@ +``` + +BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.6456/22H2/2022Update) +Intel Core i7-1065G7 CPU 1.30GHz, 1 CPU, 8 logical and 4 physical cores +.NET SDK 8.0.403 + [Host] : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI + Job-UAYNDI : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI + +InvocationCount=1 UnrollFactor=1 + +``` +| Method | Behavior | Strategy | BaseSpanSize | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated | +|---------- |---------- |----------- |------------- |--------:|---------:|---------:|----------:|----------:|----------:|------------:| +| **Rebalance** | **Fixed** | **Snapshot** | **100** | **1.088 s** | **0.0006 s** | **0.0005 s** | **-** | **-** | **-** | **224.2 KB** | +| **Rebalance** | **Fixed** | **Snapshot** | **1000** | **1.075 s** | **0.0140 s** | **0.0131 s** | **-** | **-** | **-** | **1702.95 KB** | +| **Rebalance** | **Fixed** | **Snapshot** | **10000** | **1.063 s** | **0.0145 s** | **0.0136 s** | **4000.0000** | **4000.0000** | **4000.0000** | **16471.64 KB** | +| **Rebalance** | **Fixed** | **CopyOnRead** | **100** | **1.058 s** | **0.0178 s** | **0.0166 s** | **-** | **-** | **-** | **92.41 KB** | +| **Rebalance** | **Fixed** | **CopyOnRead** | **1000** | **1.061 s** | **0.0171 s** | **0.0160 s** | **-** | **-** | **-** | **351.64 KB** | +| **Rebalance** | **Fixed** | **CopyOnRead** | **10000** | **1.053 s** | **0.0095 s** | **0.0084 s** | **-** | **-** | **-** | **2495.27 KB** | +| **Rebalance** | **Growing** | **Snapshot** | **100** | **1.064 s** | **0.0120 s** | **0.0112 s** | **-** | **-** | **-** | **966.56 KB** | +| **Rebalance** | **Growing** | **Snapshot** | **1000** | **1.056 s** | **0.0209 s** | **0.0205 s** | **-** | **-** | **-** | **2443.63 KB** | +| **Rebalance** | **Growing** | **Snapshot** | **10000** | **1.047 s** | **0.0166 s** | **0.0147 s** | **4000.0000** | **4000.0000** | **4000.0000** | **17212.25 KB** | +| **Rebalance** | **Growing** | **CopyOnRead** | **100** | **1.066 s** | **0.0134 s** | **0.0125 s** | **-** | **-** | **-** | **560.24 KB** | +| **Rebalance** | **Growing** | **CopyOnRead** | **1000** | **1.064 s** | **0.0129 s** | **0.0115 s** | **-** | **-** | **-** | **883.38 KB** | +| **Rebalance** | **Growing** | **CopyOnRead** | **10000** | **1.067 s** | **0.0188 s** | **0.0176 s** | **-** | **-** | **-** | **2514.96 KB** | +| **Rebalance** | **Shrinking** | **Snapshot** | **100** | **1.068 s** | **0.0169 s** | **0.0158 s** | **-** | **-** | **-** | **687.52 KB** | +| **Rebalance** | **Shrinking** | **Snapshot** | **1000** | **1.075 s** | **0.0179 s** | **0.0168 s** | **-** | **-** | **-** | **1489.67 KB** | +| **Rebalance** | **Shrinking** | **Snapshot** | **10000** | **1.067 s** | **0.0207 s** | **0.0230 s** | **2000.0000** | **2000.0000** | **2000.0000** | **9611.98 KB** | +| **Rebalance** | **Shrinking** | **CopyOnRead** | **100** | **1.070 s** | **0.0171 s** | **0.0160 s** | **-** | **-** | **-** | **422.9 KB** | +| **Rebalance** | **Shrinking** | **CopyOnRead** | **1000** | **1.069 s** | **0.0156 s** | **0.0145 s** | **-** | **-** | **-** | **882.38 KB** | +| **Rebalance** | **Shrinking** | **CopyOnRead** | **10000** | **1.063 s** | **0.0202 s** | **0.0216 s** | **-** | **-** | **-** | **2513.97 KB** | diff --git a/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.ScenarioBenchmarks-report-github.md b/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.ScenarioBenchmarks-report-github.md new file mode 100644 index 0000000..ba89f2c --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.ScenarioBenchmarks-report-github.md @@ -0,0 +1,39 @@ +``` + +BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.6456/22H2/2022Update) +Intel Core i7-1065G7 CPU 1.30GHz, 1 CPU, 8 logical and 4 physical cores +.NET SDK 8.0.403 + [Host] : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI + Job-RNFOIY : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI + +InvocationCount=1 UnrollFactor=1 + +``` +| Method | RangeSpan | CacheCoefficientSize | Mean | Error | StdDev | Median | Ratio | RatioSD | Gen0 | Gen1 | Gen2 | Allocated | Alloc Ratio | +|------------------------------- |---------- |--------------------- |----------:|---------:|----------:|----------:|------:|--------:|----------:|----------:|----------:|------------:|------------:| +| **ColdStart_Rebalance_Snapshot** | **100** | **1** | **97.80 ms** | **1.293 ms** | **1.080 ms** | **98.15 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **7.24 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 100 | 1 | 97.69 ms | 1.302 ms | 1.154 ms | 97.99 ms | 1.00 | 0.01 | - | - | - | 8.7 KB | 1.20 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **100** | **10** | **98.04 ms** | **1.863 ms** | **1.743 ms** | **97.89 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **21.38 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 100 | 10 | 97.83 ms | 1.095 ms | 0.971 ms | 97.98 ms | 1.00 | 0.01 | - | - | - | 36.77 KB | 1.72 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **100** | **100** | **97.96 ms** | **1.362 ms** | **1.138 ms** | **98.19 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **162.22 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 100 | 100 | 97.76 ms | 1.249 ms | 1.043 ms | 98.06 ms | 1.00 | 0.01 | - | - | - | 260.84 KB | 1.61 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **1000** | **1** | **97.80 ms** | **1.138 ms** | **1.009 ms** | **97.95 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **35.58 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 1000 | 1 | 98.39 ms | 1.856 ms | 1.449 ms | 98.09 ms | 1.01 | 0.03 | - | - | - | 43.95 KB | 1.24 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **1000** | **10** | **98.36 ms** | **1.555 ms** | **1.298 ms** | **97.93 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **176.42 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 1000 | 10 | 98.06 ms | 0.791 ms | 0.740 ms | 98.24 ms | 1.00 | 0.02 | - | - | - | 268.02 KB | 1.52 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **1000** | **100** | **98.37 ms** | **1.871 ms** | **2.155 ms** | **98.13 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **1582.74 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 1000 | 100 | 97.36 ms | 1.573 ms | 1.314 ms | 97.68 ms | 0.99 | 0.02 | - | - | - | 2060.09 KB | 1.30 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **10000** | **1** | **97.63 ms** | **1.349 ms** | **1.127 ms** | **97.84 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **342.13 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 10000 | 1 | 98.20 ms | 1.582 ms | 1.235 ms | 97.85 ms | 1.01 | 0.02 | - | - | - | 363.41 KB | 1.06 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **10000** | **10** | **97.41 ms** | **1.768 ms** | **1.381 ms** | **97.93 ms** | **1.00** | **0.00** | **-** | **-** | **-** | **1748.45 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 10000 | 10 | 97.67 ms | 0.927 ms | 0.723 ms | 97.91 ms | 1.00 | 0.01 | - | - | - | 2155.48 KB | 1.23 | +| | | | | | | | | | | | | | | +| **ColdStart_Rebalance_Snapshot** | **10000** | **100** | **130.46 ms** | **2.613 ms** | **7.497 ms** | **129.33 ms** | **1.00** | **0.00** | **1000.0000** | **1000.0000** | **1000.0000** | **15811.91 KB** | **1.00** | +| ColdStart_Rebalance_CopyOnRead | 10000 | 100 | 151.16 ms | 8.120 ms | 23.942 ms | 141.97 ms | 1.17 | 0.20 | 2000.0000 | 2000.0000 | 2000.0000 | 16492.75 KB | 1.04 | diff --git a/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.UserFlowBenchmarks-report-github.md b/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.UserFlowBenchmarks-report-github.md new file mode 100644 index 0000000..609b285 --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/Results/SlidingWindowCache.Benchmarks.Benchmarks.UserFlowBenchmarks-report-github.md @@ -0,0 +1,111 @@ +``` + +BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.6456/22H2/2022Update) +Intel Core i7-1065G7 CPU 1.30GHz, 1 CPU, 8 logical and 4 physical cores +.NET SDK 8.0.403 + [Host] : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI + Job-OPIWYK : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI + +InvocationCount=1 UnrollFactor=1 + +``` +| Method | RangeSpan | CacheCoefficientSize | Mean | Error | StdDev | Median | Ratio | RatioSD | Allocated | Alloc Ratio | +|----------------------------------------- |---------- |--------------------- |-------------:|-------------:|-------------:|-------------:|-------:|--------:|------------:|------------:| +| **User_FullHit_Snapshot** | **100** | **1** | **28.48 μs** | **2.805 μs** | **7.726 μs** | **28.25 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 100 | 1 | 37.16 μs | 5.201 μs | 15.172 μs | 37.90 μs | 1.37 | 0.46 | 2.51 KB | 1.42 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **100** | **10** | **25.72 μs** | **2.020 μs** | **5.598 μs** | **22.20 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 100 | 10 | 47.16 μs | 8.119 μs | 23.294 μs | 54.30 μs | 1.82 | 0.70 | 6.77 KB | 3.83 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **100** | **100** | **25.93 μs** | **2.438 μs** | **6.756 μs** | **26.20 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 100 | 100 | 71.48 μs | 7.908 μs | 23.067 μs | 78.00 μs | 2.84 | 0.61 | 49.38 KB | 27.96 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **1000** | **1** | **28.51 μs** | **3.773 μs** | **10.517 μs** | **28.55 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 1000 | 1 | 47.99 μs | 8.341 μs | 24.330 μs | 54.10 μs | 1.76 | 0.66 | 8.84 KB | 5.00 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **1000** | **10** | **24.74 μs** | **2.854 μs** | **7.861 μs** | **25.45 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 1000 | 10 | 71.17 μs | 7.872 μs | 22.964 μs | 76.75 μs | 3.12 | 0.98 | 51.06 KB | 28.92 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **1000** | **100** | **20.91 μs** | **3.697 μs** | **10.489 μs** | **17.15 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 1000 | 100 | 153.77 μs | 10.768 μs | 30.895 μs | 150.45 μs | 8.89 | 3.74 | 473.08 KB | 267.94 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **10000** | **1** | **14.91 μs** | **2.769 μs** | **7.810 μs** | **13.30 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 10000 | 1 | 63.34 μs | 7.619 μs | 22.224 μs | 62.70 μs | 4.99 | 2.16 | 72.12 KB | 40.85 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **10000** | **10** | **30.79 μs** | **8.644 μs** | **25.487 μs** | **15.95 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 10000 | 10 | 193.62 μs | 10.014 μs | 28.893 μs | 196.80 μs | 12.00 | 8.52 | 494.03 KB | 279.81 | +| | | | | | | | | | | | +| **User_FullHit_Snapshot** | **10000** | **100** | **16.87 μs** | **4.122 μs** | **11.143 μs** | **13.70 μs** | **1.00** | **0.00** | **1.77 KB** | **1.00** | +| User_FullHit_CopyOnRead | 10000 | 100 | 1,574.74 μs | 203.654 μs | 600.478 μs | 1,258.85 μs | 124.15 | 72.36 | 4713.2 KB | 2,669.42 | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **100** | **1** | **37.90 μs** | **5.039 μs** | **13.794 μs** | **39.40 μs** | **?** | **?** | **5.45 KB** | **?** | +| User_FullMiss_CopyOnRead | 100 | 1 | 40.12 μs | 2.281 μs | 6.089 μs | 39.20 μs | ? | ? | 5.45 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **100** | **10** | **62.61 μs** | **2.718 μs** | **7.303 μs** | **61.25 μs** | **?** | **?** | **26.63 KB** | **?** | +| User_FullMiss_CopyOnRead | 100 | 10 | 67.76 μs | 5.211 μs | 14.264 μs | 63.50 μs | ? | ? | 26.63 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **100** | **100** | **243.24 μs** | **12.174 μs** | **32.912 μs** | **249.60 μs** | **?** | **?** | **209.86 KB** | **?** | +| User_FullMiss_CopyOnRead | 100 | 100 | 254.16 μs | 4.038 μs | 7.177 μs | 252.25 μs | ? | ? | 209.86 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **1000** | **1** | **69.86 μs** | **2.952 μs** | **7.828 μs** | **69.75 μs** | **?** | **?** | **30.07 KB** | **?** | +| User_FullMiss_CopyOnRead | 1000 | 1 | 70.67 μs | 2.214 μs | 5.948 μs | 69.55 μs | ? | ? | 30.07 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **1000** | **10** | **223.71 μs** | **17.981 μs** | **48.611 μs** | **246.00 μs** | **?** | **?** | **212.67 KB** | **?** | +| User_FullMiss_CopyOnRead | 1000 | 10 | 258.50 μs | 4.766 μs | 11.047 μs | 255.60 μs | ? | ? | 212.67 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **1000** | **100** | **2,048.49 μs** | **148.508 μs** | **391.230 μs** | **2,170.60 μs** | **?** | **?** | **1812.57 KB** | **?** | +| User_FullMiss_CopyOnRead | 1000 | 100 | 2,071.37 μs | 162.848 μs | 423.263 μs | 2,187.60 μs | ? | ? | 1812.57 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **10000** | **1** | **338.11 μs** | **6.745 μs** | **16.545 μs** | **342.95 μs** | **?** | **?** | **247.76 KB** | **?** | +| User_FullMiss_CopyOnRead | 10000 | 1 | 341.64 μs | 7.774 μs | 20.884 μs | 345.10 μs | ? | ? | 247.76 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **10000** | **10** | **2,105.68 μs** | **151.099 μs** | **400.692 μs** | **2,235.30 μs** | **?** | **?** | **1847.02 KB** | **?** | +| User_FullMiss_CopyOnRead | 10000 | 10 | 2,110.47 μs | 146.844 μs | 381.668 μs | 2,254.40 μs | ? | ? | 1847.02 KB | ? | +| | | | | | | | | | | | +| **User_FullMiss_Snapshot** | **10000** | **100** | **10,537.49 μs** | **1,543.784 μs** | **4,303.452 μs** | **8,193.50 μs** | **?** | **?** | **16047.32 KB** | **?** | +| User_FullMiss_CopyOnRead | 10000 | 100 | 12,561.95 μs | 1,894.852 μs | 5,282.089 μs | 10,489.10 μs | ? | ? | 16047.32 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **100** | **1** | **58.72 μs** | **5.008 μs** | **14.042 μs** | **55.80 μs** | **?** | **?** | **5.34 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 100 | 1 | 76.70 μs | 9.082 μs | 26.779 μs | 64.45 μs | ? | ? | 5.34 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 100 | 1 | 52.41 μs | 2.378 μs | 6.306 μs | 51.30 μs | ? | ? | 5.28 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 100 | 1 | 67.44 μs | 9.796 μs | 28.263 μs | 54.55 μs | ? | ? | 5.29 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **100** | **10** | **106.46 μs** | **2.497 μs** | **6.707 μs** | **105.40 μs** | **?** | **?** | **19.61 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 100 | 10 | 137.94 μs | 11.584 μs | 31.317 μs | 127.10 μs | ? | ? | 19.62 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 100 | 10 | 84.91 μs | 2.562 μs | 6.703 μs | 83.80 μs | ? | ? | 19.55 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 100 | 10 | 101.34 μs | 5.741 μs | 14.716 μs | 98.40 μs | ? | ? | 19.56 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **100** | **100** | **524.70 μs** | **37.092 μs** | **99.646 μs** | **560.45 μs** | **?** | **?** | **161.86 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 100 | 100 | 756.21 μs | 22.660 μs | 57.677 μs | 760.10 μs | ? | ? | 161.87 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 100 | 100 | 403.43 μs | 12.364 μs | 33.638 μs | 405.50 μs | ? | ? | 161.8 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 100 | 100 | 485.43 μs | 15.330 μs | 39.019 μs | 490.10 μs | ? | ? | 161.81 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **1000** | **1** | **127.79 μs** | **3.147 μs** | **8.454 μs** | **125.55 μs** | **?** | **?** | **26.5 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 1000 | 1 | 154.75 μs | 3.086 μs | 7.570 μs | 154.00 μs | ? | ? | 26.51 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 1000 | 1 | 100.85 μs | 2.402 μs | 6.413 μs | 100.40 μs | ? | ? | 26.45 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 1000 | 1 | 113.48 μs | 4.102 μs | 10.440 μs | 112.65 μs | ? | ? | 26.45 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **1000** | **10** | **723.19 μs** | **14.291 μs** | **36.634 μs** | **724.40 μs** | **?** | **?** | **167.48 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 1000 | 10 | 755.95 μs | 33.956 μs | 90.045 μs | 773.85 μs | ? | ? | 167.49 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 1000 | 10 | 406.49 μs | 5.312 μs | 10.609 μs | 407.40 μs | ? | ? | 167.43 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 1000 | 10 | 508.24 μs | 4.750 μs | 11.288 μs | 505.50 μs | ? | ? | 167.44 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **1000** | **100** | **6,129.94 μs** | **385.340 μs** | **1,136.183 μs** | **6,620.25 μs** | **?** | **?** | **1575.21 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 1000 | 100 | 6,446.39 μs | 419.097 μs | 1,202.469 μs | 6,850.55 μs | ? | ? | 1575.22 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 1000 | 100 | 4,377.79 μs | 282.570 μs | 828.730 μs | 4,685.00 μs | ? | ? | 1575.16 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 1000 | 100 | 3,820.06 μs | 305.845 μs | 826.869 μs | 4,047.25 μs | ? | ? | 1575.16 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **10000** | **1** | **696.49 μs** | **15.555 μs** | **42.320 μs** | **719.00 μs** | **?** | **?** | **237.66 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 10000 | 1 | 787.21 μs | 53.590 μs | 157.169 μs | 701.20 μs | ? | ? | 237.66 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 10000 | 1 | 778.11 μs | 5.062 μs | 8.174 μs | 778.05 μs | ? | ? | 237.6 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 10000 | 1 | 811.02 μs | 46.978 μs | 138.516 μs | 742.15 μs | ? | ? | 237.61 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **10000** | **10** | **6,598.57 μs** | **269.099 μs** | **758.997 μs** | **6,764.45 μs** | **?** | **?** | **1644.12 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 10000 | 10 | 6,963.86 μs | 326.050 μs | 881.496 μs | 7,310.30 μs | ? | ? | 1644.13 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 10000 | 10 | 3,315.61 μs | 310.699 μs | 802.013 μs | 3,697.05 μs | ? | ? | 1644.06 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 10000 | 10 | 4,343.07 μs | 328.320 μs | 847.498 μs | 4,653.60 μs | ? | ? | 1644.07 KB | ? | +| | | | | | | | | | | | +| **User_PartialHit_ForwardShift_Snapshot** | **10000** | **100** | **27,304.27 μs** | **1,686.910 μs** | **4,812.849 μs** | **25,289.10 μs** | **?** | **?** | **15708.09 KB** | **?** | +| User_PartialHit_ForwardShift_CopyOnRead | 10000 | 100 | 36,889.53 μs | 2,344.198 μs | 6,911.922 μs | 35,258.20 μs | ? | ? | 15708.38 KB | ? | +| User_PartialHit_BackwardShift_Snapshot | 10000 | 100 | 21,344.69 μs | 1,804.776 μs | 5,235.982 μs | 19,536.40 μs | ? | ? | 15708.31 KB | ? | +| User_PartialHit_BackwardShift_CopyOnRead | 10000 | 100 | 23,614.83 μs | 2,215.154 μs | 6,531.432 μs | 23,086.85 μs | ? | ? | 15708.32 KB | ? | diff --git a/benchmarks/SlidingWindowCache.Benchmarks/SlidingWindowCache.Benchmarks.csproj b/benchmarks/SlidingWindowCache.Benchmarks/SlidingWindowCache.Benchmarks.csproj new file mode 100644 index 0000000..336f07e --- /dev/null +++ b/benchmarks/SlidingWindowCache.Benchmarks/SlidingWindowCache.Benchmarks.csproj @@ -0,0 +1,26 @@ + + + + net8.0 + enable + enable + false + Exe + + + + + + + + + + + + + + + + + + diff --git a/docs/actors-and-responsibilities.md b/docs/actors-and-responsibilities.md new file mode 100644 index 0000000..2a9daec --- /dev/null +++ b/docs/actors-and-responsibilities.md @@ -0,0 +1,247 @@ +# Sliding Window Cache — System Actors & Invariant Ownership + +This document maps **system actors** to the invariants they enforce or guarantee. + +--- + +## 1. User Path (Fast Path / Read Path Actor) + +**Role:** +Handles user requests with minimal latency and maximal isolation from background processes. + +**Implementation:** +**Internal class:** `UserRequestHandler` (in `UserPath/` namespace) +**Public facade:** `WindowCache` delegates all requests to UserRequestHandler + +**Execution Context:** +**Lives in: User Thread** + +**Critical Contract:** +``` +Every user access produces a rebalance intent containing delivered data. +The UserRequestHandler is READ-ONLY with respect to cache state. +The UserRequestHandler NEVER invokes directly decision logic - it just publishes an intent. +``` + +**Responsible for invariants:** +- -1. User Path and Rebalance Execution never write to cache concurrently +- 0. User Path has higher priority than rebalance execution +- 0a. Every User Request MUST cancel any ongoing or pending Rebalance Execution to prevent interference +- 1. User Path always serves user requests +- 2. User Path never waits for rebalance execution +- 3. User Path is the sole source of rebalance intent +- 5. Performs only work necessary to return data +- 6. May synchronously request from IDataSource +- 7. May read cache and source, but does not mutate cache state +- 8. (NEW) MUST NOT mutate cache under any circumstance (read-only) +- 9a. Cache data MUST always remain contiguous (no gaps allowed) +- 10. Always returns exactly RequestedRange +- 24e. Intent MUST contain delivered data (RangeData) +- 24f. Delivered data represents what user actually received + +**Explicit Non-Responsibilities:** +- ❌ **NEVER checks NoRebalanceRange** (belongs to DecisionEngine) +- ❌ **NEVER computes DesiredCacheRange** (belongs to GeometryPolicy) +- ❌ **NEVER decides whether to rebalance** (belongs to DecisionEngine) +- ❌ **NEVER writes to cache** (no Rematerialize calls) +- ❌ **NEVER writes to LastRequested** +- ❌ **NEVER writes to NoRebalanceRange** + +**Responsibility Type:** ensures and enforces fast, correct user access with strict read-only boundaries + +--- + +## 2. Rebalance Decision Engine (Pure Decision Actor) + +**Role:** +Analyzes the need for rebalance and forms intents without mutating system state. + +**Execution Context:** +**Lives in: Background / ThreadPool** + +**Visibility:** +- **Not visible to User Path** +- Invoked only by RebalanceIntentManager +- May execute many times, results may be discarded + +**Critical Rule:** +``` +DecisionEngine lives strictly inside the background contour. +``` + +**Responsible for invariants:** +- 24. Decision Path is purely analytical +- 25. Never mutates cache state +- 26. No rebalance if inside NoRebalanceRange +- 27. No rebalance if DesiredCacheRange == CurrentCacheRange +- 28. Rebalance triggered only if confirmed necessary + +**Responsibility Type:** ensures correctness of decisions + +**Note:** Not a top-level actor — internal tool of IntentManager/Executor pipeline. + +--- + +## 3. Cache Geometry Policy (Configuration & Policy Actor) + +**Role:** +Defines canonical sliding window shape and rules. + +**Implementation:** +This logical actor is internally decomposed into two components for separation of concerns: +- **ThresholdRebalancePolicy** - Computes NoRebalanceRange, checks threshold-based triggering +- **ProportionalRangePlanner** - Computes DesiredCacheRange, plans cache geometry + +**Execution Context:** +**Lives in: Background / ThreadPool** (invoked by RebalanceDecisionEngine) + +**Responsible for invariants:** +- 29. DesiredCacheRange computed from RequestedRange + config [ProportionalRangePlanner] +- 30. Independent of current cache contents [ProportionalRangePlanner] +- 31. Canonical target cache state [ProportionalRangePlanner] +- 32. Sliding window geometry defined by configuration [Both components] +- 33. NoRebalanceRange derived from current cache range + config [ThresholdRebalancePolicy] + +**Responsibility Type:** sets rules and constraints + +**Note:** Internally decomposed into two components that handle different aspects: +- **When to rebalance** (threshold rules) → ThresholdRebalancePolicy +- **What shape to target** (cache geometry) → ProportionalRangePlanner + +--- + +## 4. Rebalance Intent Manager (Intent & Concurrency Actor) + +**Role:** +Manages lifecycle of rebalance intents and prevents races and stale applications. + +**Implementation:** +This logical actor is internally decomposed into two components for separation of concerns: +- **IntentController** (Intent Controller) - intent identity, lifecycle, cancellation +- **RebalanceScheduler** (Execution Scheduler) - timing, debounce, pipeline orchestration (stateless, plus Task tracking for infrastructure/testing) + +**Execution Context:** +**Lives in: Background / ThreadPool** + +**Enhanced Role (Corrected Model):** + +Now responsible for: +- **Receiving intents** (on every user request) [Intent Controller] +- **Intent identity and versioning** [Intent Controller] +- **Cancellation** of obsolete intents [Intent Controller] +- **Deduplication** and debouncing [Execution Scheduler] +- **Single-flight execution** enforcement [Execution Scheduler] +- **Starting background tasks** [Execution Scheduler] +- **Orchestrating the decision pipeline**: [Execution Scheduler] + 1. Invoke DecisionEngine + 2. If allowed, invoke Executor + 3. Handle cancellation + +**Authority:** *Owns time and concurrency.* + +**Responsible for invariants:** +- 17. At most one active rebalance intent +- 18. Older intents become obsolete +- 19. Executions can be cancelled or ignored +- 20. Obsolete intent must not start execution +- 21. At most one rebalance execution active +- 22. Execution reflects latest access pattern +- 23. System eventually stabilizes under load +- 24. Intent does not guarantee execution - execution is opportunistic + +**Responsibility Type:** controls and coordinates intent execution + +**Note:** Internally decomposed into Intent Controller + Execution Scheduler, +but externally appears as a single unified actor. + +--- + +## 5. Rebalance Executor (Single-Writer Actor) + +**Role:** +The **ONLY component** that mutates cache state (single-writer architecture). Responsible for cache normalization using delivered data from intent as authoritative source. + +**Execution Context:** +**Lives in: Background / ThreadPool** + +**Single-Writer Guarantee:** +Rebalance Executor is the ONLY component that mutates: +- Cache data and range (via `Cache.Rematerialize()`) +- `LastRequested` field +- `NoRebalanceRange` field + +This eliminates race conditions and ensures consistent cache state. + +**Responsible for invariants:** +- 4. Rebalance is asynchronous relative to User Path +- 34. MUST support cancellation at all stages +- 34a. MUST yield to User Path requests immediately upon cancellation +- 34b. Partially executed or cancelled execution MUST NOT leave cache inconsistent +- 35. Only path responsible for cache normalization +- 35a. Mutates cache ONLY for normalization, using delivered data from intent: + - Uses delivered data from intent as authoritative base (not current cache) + - Expanding to DesiredCacheRange by fetching only truly missing ranges + - Trimming excess data outside DesiredCacheRange + - Writing to Cache.Rematerialize() + - Writing to LastRequested + - Recomputing NoRebalanceRange +- 36. May replace / expand / shrink cache to achieve normalization +- 37. Requests data only for missing subranges (not covered by delivered data) +- 38. Does not overwrite intersecting data +- 39. Upon completion: CacheData corresponds to DesiredCacheRange +- 40. Upon completion: CurrentCacheRange == DesiredCacheRange +- 41. Upon completion: NoRebalanceRange recomputed + +**Responsibility Type:** executes rebalance and normalizes cache (cancellable, never concurrent with User Path) + +--- + +## 6. Cache State Manager (Consistency & Atomicity Actor) + +**Role:** +Ensures atomicity and internal consistency of cache state, coordinates cancellation between User Path and Rebalance Execution. + +**Responsible for invariants:** +- 11. CacheData and CurrentCacheRange are consistent +- 12. Changes applied atomically +- 13. No permanent inconsistent state +- 14. Temporary inefficiencies are acceptable +- 15. Partial / cancelled execution cannot break consistency +- 16. Only latest intent results may be applied +- 0a. Coordinates cancellation: User Request cancels ongoing/pending Rebalance before mutation + +**Responsibility Type:** guarantees state correctness and mutual exclusion + +--- + +## 🧠 Architectural Summary + +- **User Path:** speed and availability +- **Decision Engine:** pure logic +- **Intent Manager:** temporal correctness and concurrency +- **Executor:** mutation +- **State Manager:** correctness and consistency +- **Geometry Policy:** deterministic cache shape + +--- + +# Sliding Window Cache — Actors vs Scenarios Reference + +This table maps **actors** to the scenarios they participate in and clarifies **read/write responsibilities**. + +| Scenario | User Path | Decision Engine | Geometry Policy | Intent Manager | Rebalance Executor | Cache State Manager | Notes | +|-----------------------------------------|----------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------|----------------------------|------------------------------------------|--------------------------------------------------------|--------------------------------------------------------|--------------------------------------------| +| **U1 – Cold Cache** | Requests data from IDataSource, updates LastRequestedRange & CurrentCacheRange, triggers rebalance | – | Computes DesiredCacheRange | Receives intent | Executes rebalance asynchronously | Validates atomic update of CacheData/CurrentCacheRange | User served directly | +| **U2 – Full Cache Hit (Exact)** | Reads from cache, updates LastRequestedRange, triggers rebalance | Checks NoRebalanceRange | Computes DesiredCacheRange | Receives intent | Executes if rebalance required | Monitors consistency | Minimal I/O | +| **U3 – Full Cache Hit (Shifted)** | Reads subrange from cache, updates LastRequestedRange, triggers rebalance | Checks NoRebalanceRange | Computes DesiredCacheRange | Receives intent | Executes if rebalance required | Monitors consistency | Cache hit but different LastRequestedRange | +| **U4 – Partial Cache Hit** | Reads intersection, requests missing from IDataSource, merges, updates LastRequestedRange, triggers rebalance | Checks NoRebalanceRange | Computes DesiredCacheRange | Receives intent | Executes merge and normalization | Ensures atomic merge & consistency | Temporary excess data allowed | +| **U5 – Full Cache Miss (Jump)** | Requests full range from IDataSource, replaces CacheData/CurrentCacheRange, updates LastRequestedRange, triggers rebalance | Checks NoRebalanceRange | Computes DesiredCacheRange | Receives intent | Executes full normalization | Ensures atomic replacement | No cached data usable | +| **D1 – NoRebalanceRange Block** | – | Checks NoRebalanceRange, decides no execution | – | Receives intent (blocked) | – | – | Fast path skip | +| **D2 – Desired == Current** | – | Computes DesiredCacheRange, decides no execution | Computes DesiredCacheRange | Receives intent (no-op) | – | – | No mutation required | +| **D3 – Rebalance Required** | – | Computes DesiredCacheRange, confirms execution | Computes DesiredCacheRange | Issues rebalance intent | Executes rebalance | Ensures consistency | Rebalance triggered asynchronously | +| **R1 – Build from Scratch** | – | – | Defines DesiredCacheRange | Receives intent | Requests full range, replaces cache | Atomic replacement | Cache initialized from empty | +| **R2 – Expand Cache (Partial Overlap)** | – | – | Defines DesiredCacheRange | Receives intent | Requests missing subranges, merges with existing cache | Atomic merge, consistency | Cache partially reused | +| **R3 – Shrink / Normalize** | – | – | Defines DesiredCacheRange | Receives intent | Trims cache to DesiredCacheRange | Atomic trim, consistency | Cache normalized to target | +| **C1 – Rebalance Trigger Pending** | Executes normally | – | – | Debounces old intent, allows only latest | Cancels obsolete | Ensures atomicity | Fast user response guaranteed | +| **C2 – Rebalance Executing** | Executes normally | – | – | Marks latest intent | Cancels or discards obsolete execution | Ensures atomicity | Latest execution wins | +| **C3 – Spike / Multiple Requests** | Executes normally | – | – | Debounces & coordinates intents | Executes only latest rebalance | Ensures atomicity | Single-flight execution enforced | \ No newline at end of file diff --git a/docs/actors-to-components-mapping.md b/docs/actors-to-components-mapping.md new file mode 100644 index 0000000..f913791 --- /dev/null +++ b/docs/actors-to-components-mapping.md @@ -0,0 +1,584 @@ +# Sliding Window Cache — Actors to Components Mapping + +This document maps the **conceptual system actors** defined by the Scenario Model +to **concrete architectural components** of the Sliding Window Cache library. + +The purpose of this document is: + +- to fix architectural intent +- to clarify responsibility boundaries +- to guide refactoring and further development +- to serve as long-term documentation for contributors and reviewers + +Actors are **stable roles**, not execution paths and not necessarily 1:1 with classes. + +--- + +## High-Level Structure + +### Execution Context Flow + +``` +═══════════════════════════════════════════════════════════ +User Thread +═══════════════════════════════════════════════════════════ + +┌───────────────────────┐ +│ SlidingWindowCache │ ← Public Facade +└───────────┬───────────┘ + │ + ▼ +┌───────────────────────┐ +│ UserRequestHandler │ ← Fast user-facing logic +└───────────┬───────────┘ + │ + │ publish rebalance intent (fire-and-forget) + │ + ▼ + +═══════════════════════════════════════════════════════════ +Background / ThreadPool +═══════════════════════════════════════════════════════════ + +┌───────────────────────────┐ +│ RebalanceIntentManager │ ← Temporal Authority +│ │ • debounce / cancel obsolete +│ │ • enforce single-flight +└───────────┬───────────────┘ • schedule execution + │ + │ invoke decision pipeline + │ + ▼ +┌───────────────────────────┐ +│ RebalanceDecisionEngine │ ← Pure Decision Logic +│ │ • NoRebalanceRange check +│ + CacheGeometryPolicy │ • DesiredCacheRange computation +└───────────┬───────────────┘ • allow/block execution + │ + │ if execution allowed + │ + ▼ +┌───────────────────────────┐ +│ RebalanceExecutor │ ← Mutating Actor +└───────────┬───────────────┘ + │ + │ atomic mutation + │ + ▼ +┌───────────────────────────┐ +│ CacheStateManager │ ← Consistency Guardian +└───────────────────────────┘ +``` + +--- + +## 1. SlidingWindowCache (Public Facade) + +### Role + +The single public entry point of the library. + +### Implementation + +**Implemented as:** `WindowCache` class + +### Responsibilities + +- Exposes the public API +- Owns configuration and lifecycle +- Wires internal components together (composition root) +- **Delegates all user requests to UserRequestHandler** +- Does **not** implement business logic itself + +### Actor Coverage + +- Acts as a **composition root** and **pure facade** +- Does **not** directly correspond to a scenario actor +- All behavioral logic is delegated to internal actors + +### Architecture Pattern + +WindowCache implements the **Facade Pattern**: +- Public interface: `IWindowCache.GetDataAsync(...)` +- Internal delegation: Forwards all requests to `UserRequestHandler.HandleRequestAsync(...)` +- Composition: Wires together all internal actors (UserRequestHandler, IntentController, DecisionEngine, Executor) + +### Notes + +This component should remain thin. +It delegates all behavioral logic to internal actors. + +**Key architectural principle:** WindowCache is a **pure facade** - it contains no business logic, only composition and delegation. + +--- + +## 2. UserRequestHandler + +*(Fast Path / Read Path Actor)* + +### Mapped Actor + +**User Path (Fast Path / Read Path Actor)** + +### Implementation + +**Implemented as:** internal class `UserRequestHandler` in `UserPath/` namespace + +### Execution Context + +**Lives in: User Thread** + +### Responsibilities + +- Handles user requests synchronously +- Decides how to serve RequestedRange: + - from cache + - from IDataSource + - or mixed +- Updates: + - LastRequestedRange + - CacheData / CurrentCacheRange **only to cover RequestedRange** +- Triggers rebalance intent +- Never blocks on rebalance + +### Critical Contract + +``` +Every user access produces a rebalance intent. +The UserRequestHandler NEVER invokes decision logic. +``` + +### Explicit Non-Responsibilities + +- No cache normalization +- No trimming or shrinking +- No rebalance execution +- No concurrency control +- **NEVER checks NoRebalanceRange** (belongs to DecisionEngine) +- **NEVER computes DesiredCacheRange** (belongs to GeometryPolicy) +- **NEVER decides whether to rebalance** (belongs to DecisionEngine) + +### Key Guarantees + +- Always returns exactly RequestedRange +- Always responds, regardless of rebalance state + +### Implementation Note + +Invoked by WindowCache via delegation: +```csharp +// WindowCache.GetDataAsync(...) implementation: +return _userRequestHandler.HandleRequestAsync(requestedRange, cancellationToken); +``` + +--- + +## 3. RebalanceDecisionEngine + +*(Pure Decision Actor)* + +### Mapped Actor + +**Rebalance Decision Engine** + +### Execution Context + +**Lives in: Background / ThreadPool** + +### Visibility + +- **Not visible to User Path** +- Invoked only by RebalanceScheduler +- May execute many times, results may be discarded + +### Critical Rule + +``` +DecisionEngine lives strictly inside the background contour. +``` + +### Responsibilities + +- Evaluates whether rebalance is required +- Checks: + - NoRebalanceRange + - DesiredCacheRange vs CurrentCacheRange +- Produces a boolean decision + +### Characteristics + +- Pure +- Deterministic +- Side-effect free +- Does not mutate cache state + +### Notes + +This component should be: + +- easily testable +- fully synchronous +- independent of execution context + +**Not a top-level actor** — internal tool of IntentManager/Executor pipeline. + +--- + +## 4. CacheGeometryPolicy + +*(Configuration & Policy Actor)* + +### Mapped Actor + +**Cache Geometry Policy** + +### Implementation + +**Implemented as:** Two separate components working together as a unified policy: + +1. **ThresholdRebalancePolicy** + - `internal readonly struct ThresholdRebalancePolicy` + - File: `src/SlidingWindowCache/CacheRebalance/Policy/ThresholdRebalancePolicy.cs` + - Computes `NoRebalanceRange` + - Checks if rebalance is needed based on threshold rules + +2. **ProportionalRangePlanner** + - `internal readonly struct ProportionalRangePlanner` + - File: `src/SlidingWindowCache/DesiredRangePlanner/ProportionalRangePlanner.cs` + - Computes `DesiredCacheRange` + - Plans canonical cache geometry based on proportional expansion + +**Key Principle:** The logical actor (Cache Geometry Policy) is decomposed into +two cooperating components for separation of concerns. Each component handles +one aspect of cache geometry: thresholds (when to rebalance) and planning (what +shape to target). + +**Used by:** RebalanceDecisionEngine composes both components to make rebalance decisions. + +### Execution Context + +**Lives in: Background / ThreadPool** (invoked by RebalanceDecisionEngine) + +### Component Responsibilities + +#### ThresholdRebalancePolicy (Threshold Rules) +- Computes `NoRebalanceRange` from `CurrentCacheRange` + threshold configuration +- Determines if requested range falls outside no-rebalance zone +- Enforces threshold-based rebalance triggering rules +- Configuration: `LeftThreshold`, `RightThreshold` + +#### ProportionalRangePlanner (Shape Planning) +- Computes `DesiredCacheRange` from `RequestedRange` + size configuration +- Defines canonical cache shape by expanding request proportionally +- Independent of current cache contents (pure function of request + config) +- Configuration: `LeftCacheSize`, `RightCacheSize` + +### Responsibilities + +Together, these components: +- Compute `DesiredCacheRange` [ProportionalRangePlanner] +- Compute `NoRebalanceRange` [ThresholdRebalancePolicy] +- Encapsulate all sliding window rules: + - left/right sizes [ProportionalRangePlanner] + - thresholds [ThresholdRebalancePolicy] + - expansion rules [ProportionalRangePlanner] + +### Characteristics + +- Stateless (both are readonly structs) +- Fully configuration-driven +- Independent of cache contents +- Pure functions (deterministic, no side effects) + +### Notes + +This actor defines the **canonical shape** of the cache. + +The split into two components reflects separation of concerns: +- **When to rebalance** (threshold-based triggering) → ThresholdRebalancePolicy +- **What shape to target** (desired cache geometry) → ProportionalRangePlanner + +Similar to RebalanceIntentManager, this logical actor is internally decomposed +but externally appears as a unified policy concept. + +--- + +## 5. RebalanceIntentManager + +*(Intent & Concurrency Actor)* + +### Mapped Actor + +**Rebalance Intent Manager** + +### Implementation + +**Implemented as:** Two internal components working together as a unified actor: + +1. **IntentController** + - `internal class IntentController` + - File: `src/SlidingWindowCache/CacheRebalance/IntentController.cs` + - Owns intent identity and cancellation lifecycle + - Exposes `CancelPendingRebalance()` and `PublishIntent()` to User Path + +2. **RebalanceScheduler (Execution Scheduler)** + - `internal class RebalanceScheduler` + - File: `src/SlidingWindowCache/CacheRebalance/RebalanceScheduler.cs` + - Owns debounce timing and background execution + - Orchestrates DecisionEngine → Executor pipeline + - Ensures single-flight execution + - **Intentionally stateless** - does not own intent identity + - **Task tracking** - provides `WaitForIdleAsync()` for deterministic synchronization (infrastructure/testing) + +**Key Principle:** The logical actor (Rebalance Intent Manager) is decomposed into +two cooperating components for separation of concerns, but externally appears as +a single unified actor. + +### Execution Context + +**Lives in: Background / ThreadPool** + +### Enhanced Role (Corrected Model) + +The Rebalance Intent Manager actor is responsible for: + +- **Receiving intents** (on every user request) [Intent Controller responsibility] +- **Intent lifecycle management** (identity, versioning) [Intent Controller responsibility] +- **Cancellation** of obsolete intents [Intent Controller responsibility] +- **Deduplication** and debouncing [Execution Scheduler responsibility] +- **Single-flight execution** enforcement [Execution Scheduler responsibility] +- **Starting background tasks** [Execution Scheduler responsibility] +- **Orchestrating the decision pipeline**: [Execution Scheduler responsibility] + 1. Invoke DecisionEngine + 2. If allowed, invoke Executor + 3. Handle cancellation + +### Component Responsibilities + +#### Intent Controller (IntentController) +- Owns `CancellationTokenSource` for current intent +- Provides `CancelPendingRebalance()` for User Path priority +- Provides `PublishIntent()` to receive new intents +- Invalidates previous intent when new intent arrives +- Does NOT perform scheduling or timing logic +- Does NOT orchestrate execution pipeline +- **Lock-free implementation** using `Interlocked.Exchange` for atomic operations +- **Thread-safe without locks** - no race conditions, no blocking +- Validated by `ConcurrencyStabilityTests` under concurrent load + +#### Execution Scheduler (RebalanceScheduler) +- Receives intent + cancellation token from Intent Controller +- Performs debounce delay +- Checks intent validity before execution starts +- Orchestrates DecisionEngine → Executor pipeline +- Ensures only one execution runs at a time (via cancellation) +- Does NOT own intent identity or versioning +- Does NOT decide whether rebalance is logically required +- Tracks background Task for deterministic synchronization (`WaitForIdleAsync()`) + +**Important**: RebalanceScheduler is intentionally stateless and does not own intent identity. +All intent lifecycle, superseding, and cancellation semantics are delegated to the Intent Controller (IntentController). +The scheduler only receives a CancellationToken for each scheduled execution and checks its validity. + +### Key Decision Authority + +- **When to invoke decision logic** [Scheduler decides after debounce] +- **When to skip execution entirely** [DecisionEngine decides based on logic] + +### Owns + +- Intent versioning [Intent Controller] +- Cancellation tokens [Intent Controller] +- Scheduling logic [Execution Scheduler] +- Pipeline orchestration [Execution Scheduler] + +### Pipeline Orchestration (Philosophy A) + +``` +IntentManager (Intent Controller) + ├── manage intent lifecycle + └── delegate to Scheduler + ↓ + RebalanceScheduler (Execution Scheduler) + ├── debounce delay + ├── check validity + └── start pipeline + ↓ + DecisionEngine + ↓ + Executor +``` + +**Benefits:** +- Clear separation: lifecycle vs. execution +- Intent Controller pattern for versioned operations +- Decision remains pure and testable +- Executor simply executes +- Single Responsibility Principle maintained + +### Notes + +This is the **temporal authority** of the system. + +The internal decomposition is an implementation detail - from an architectural +perspective, this is a single unified actor. + +--- + +## 6. RebalanceExecutor + +*(Mutating Actor)* + +### Mapped Actor + +**Rebalance Executor** + +### Responsibilities + +- Executes rebalance when authorized +- Performs I/O with IDataSource +- Computes missing ranges +- Merges / trims / replaces cache data +- Produces normalized cache state + +### Characteristics + +- Asynchronous +- Cancellable +- Heavyweight + +### Constraints + +- Must be overwrite-safe +- Must respect cancellation +- Must never apply obsolete results + +--- + +## 7. CacheStateManager + +*(Consistency & Atomicity Actor)* + +### Mapped Actor + +**Cache State Manager** + +### Responsibilities + +- Owns CacheData and CurrentCacheRange +- Applies mutations atomically +- Guards consistency invariants +- Ensures overwrite safety + +### Notes + +This actor may be: + +- a separate component +- or a well-defined internal module + +Its **conceptual separation is mandatory** even if physically co-located. + +--- + +## Architectural Intent Summary + +| Actor | Primary Concern | +|--------------------|-------------------------| +| UserRequestHandler | Speed & availability | +| DecisionEngine | Correctness of decision | +| GeometryPolicy | Deterministic shape | +| IntentManager | Time & concurrency | +| RebalanceExecutor | Physical mutation | +| CacheStateManager | Safety & consistency | + +--- + +## Execution Context Model + +### Corrected Mental Model + +``` +User Thread +─────────── +UserRequestHandler + ├── serve request (sync) + └── publish rebalance intent (fire-and-forget) + │ + ▼ +Background / ThreadPool +─────────────────────── +RebalanceIntentManager + ├── debounce / cancel obsolete intents + ├── enforce single-flight + └── schedule execution + │ + ▼ +RebalanceDecisionEngine + ├── NoRebalanceRange check + ├── DesiredCacheRange computation + └── no-op or allow execution + │ + ▼ +RebalanceExecutor + └── mutate cache if allowed +``` + +### Key Principle + +🔑 **DecisionEngine lives strictly within the background contour.** + +### Actor Execution Contexts + +| Actor | Execution Context | Invoked By | +|----------------------------|-----------------------|--------------------------| +| UserRequestHandler | User Thread | User (public API) | +| IntentController | Background/ThreadPool | UserRequestHandler | +| RebalanceScheduler | Background/ThreadPool | IntentController | +| RebalanceDecisionEngine | Background/ThreadPool | RebalanceScheduler | +| CacheGeometryPolicy | Background/ThreadPool | RebalanceDecisionEngine | +| RebalanceExecutor | Background/ThreadPool | RebalanceScheduler | +| CacheStateManager | Both (with locking) | Both paths (coordinated) | + +### Responsibilities Refixed + +#### UserRequestHandler (Updated Role) + +- ✅ Serves user requests +- ✅ **Always publishes rebalance intent** +- ❌ **Never** checks NoRebalanceRange +- ❌ **Never** computes DesiredCacheRange +- ❌ **Never** decides "to rebalance or not" + +**Contract:** *Every user access produces a rebalance intent.* + +#### RebalanceIntentManager (Enhanced Role) + +The Rebalance Intent Manager ACTOR (implemented via IntentController + RebalanceScheduler) is the **orchestrator** responsible for: + +- ✅ Receiving intent on **every user request** [IntentController] +- ✅ Deduplication and debouncing [RebalanceScheduler] +- ✅ Cancelling obsolete intents [IntentController] +- ✅ Single-flight enforcement [Both components via cancellation] +- ✅ **Launching background task** [RebalanceScheduler] +- ✅ **Deciding when to start decision logic** [RebalanceScheduler] +- ✅ **Deciding when to skip execution** [DecisionEngine via RebalanceScheduler] +- ⚠️ **Intent does not guarantee execution** - execution is opportunistic + +**Authority:** *Owns time and concurrency.* + +#### RebalanceDecisionEngine (Clarified Role) + +**Not a top-level actor** — internal tool of IntentManager/Executor pipeline. + +- ❌ Not visible to User Path +- ✅ Invoked only in background +- ✅ Can execute many times +- ✅ Results may be discarded + +**Contract:** *Given intent + current snapshot, decide if execution is allowed.* + +--- + +This mapping is **normative**. +Future refactoring must preserve these responsibility boundaries. \ No newline at end of file diff --git a/docs/cache-state-machine.md b/docs/cache-state-machine.md new file mode 100644 index 0000000..5a452ec --- /dev/null +++ b/docs/cache-state-machine.md @@ -0,0 +1,285 @@ +# Sliding Window Cache — Cache State Machine + +This document defines the formal state machine for the Sliding Window Cache, clarifying state transitions, mutation ownership, and concurrency control. + +--- + +## States + +The cache exists in one of three states: + +### 1. **Uninitialized** +- **Definition:** Cache has no data and no range defined +- **Characteristics:** + - `CurrentCacheRange == null` + - `CacheData == null` + - `LastRequestedRange == null` + - `NoRebalanceRange == null` + +### 2. **Initialized** +- **Definition:** Cache contains valid data corresponding to a defined range +- **Characteristics:** + - `CurrentCacheRange != null` + - `CacheData != null` + - `CacheData` is consistent with `CurrentCacheRange` (Invariant 11) + - Cache is contiguous (no gaps, Invariant 9a) + - System is ready to serve user requests + +### 3. **Rebalancing** +- **Definition:** Background normalization is in progress +- **Characteristics:** + - Cache remains in `Initialized` state from external perspective + - User Path continues to serve requests normally + - Rebalance Execution is mutating cache asynchronously + - Rebalance can be cancelled at any time by User Path + +--- + +## State Transitions + +``` +┌─────────────────┐ +│ Uninitialized │ +└────────┬────────┘ + │ + │ U1: First User Request + │ (User Path populates cache) + ▼ +┌─────────────────┐ +│ Initialized │◄──────────┐ +└────────┬────────┘ │ + │ │ + │ Any User Request │ + │ triggers rebalance │ + ▼ │ +┌─────────────────┐ │ +│ Rebalancing │ │ +└────────┬────────┘ │ + │ │ + │ Rebalance │ + │ completes │ + └────────────────────┘ + + (User Request during Rebalancing) + ┌────────────────────┐ + │ Cancel Rebalance │ + │ Return to │ + │ Initialized │ + └────────────────────┘ +``` + +--- + +## Transition Details + +### T1: Uninitialized → Initialized (Cold Start) +- **Trigger:** First user request (Scenario U1) +- **Actor:** Rebalance Execution (NOT User Path) +- **Sequence:** + 1. User Path fetches `RequestedRange` from IDataSource + 2. User Path returns data to user immediately + 3. User Path publishes intent with delivered data + 4. Rebalance Execution writes to cache (first cache write) +- **Mutation:** Performed by Rebalance Execution ONLY (single-writer) + - Set `CacheData` = delivered data from intent + - Set `CurrentCacheRange` = delivered range + - Set `LastRequestedRange` = `RequestedRange` +- **Atomicity:** Changes applied atomically (Invariant 12) +- **Postcondition:** Cache enters `Initialized` state after rebalance execution completes +- **Note:** User Path is read-only; initial cache population is performed by Rebalance Execution + +### T2: Initialized → Rebalancing (Normal Operation) +- **Trigger:** User request (any scenario) +- **Actor:** User Path (reads), Rebalance Executor (writes) +- **Sequence:** + 1. User Path cancels any pending rebalance + 2. User Path reads from cache or fetches from IDataSource (NO cache mutation) + 3. User Path returns data to user immediately + 4. User Path publishes intent with delivered data + 5. Rebalance Execution writes to cache (background) +- **Mutation:** Performed by Rebalance Execution ONLY + - User Path does NOT mutate cache, LastRequested, or NoRebalanceRange + - Rebalance Execution normalizes cache to DesiredCacheRange +- **Concurrency:** User Path is read-only; no race conditions +- **Postcondition:** Cache logically enters `Rebalancing` state (background process active) + +### T3: Rebalancing → Initialized (Rebalance Completion) +- **Trigger:** Rebalance execution completes successfully +- **Actor:** Rebalance Executor (sole writer) +- **Mutation:** Performed by Rebalance Execution ONLY + - Use delivered data from intent as authoritative base + - Fetch missing data for `DesiredCacheRange` (only truly missing parts) + - Merge delivered data with fetched data + - Trim to `DesiredCacheRange` (normalization) + - Set `CacheData` and `CurrentCacheRange` via `Rematerialize()` + - Set `LastRequestedRange` = original requested range from intent + - Recompute `NoRebalanceRange` +- **Atomicity:** Changes applied atomically (Invariant 12) +- **Postcondition:** Cache returns to stable `Initialized` state + +### T4: Rebalancing → Initialized (User Request Cancels Rebalance) +- **Trigger:** User request arrives during rebalance execution (Scenarios C1, C2) +- **Actor:** User Path (cancels), Rebalance Execution (yields) +- **Sequence:** + 1. **User Path cancels ongoing/pending rebalance** (Invariant 0a) + 2. User Path reads from cache or fetches from IDataSource (NO cache mutation) + 3. User Path returns data to user immediately + 4. User Path publishes new intent with delivered data + 5. New rebalance execution begins (background) +- **Critical Rule:** User Path does NOT mutate cache; only cancels to prevent interference (Invariant 0) +- **Priority:** User Path always has priority, ensured via cancellation not mutation exclusion +- **Note:** Cancelled rebalance yields; new rebalance uses new intent's delivered data + +--- + +## Mutation Ownership Matrix + +| State | User Path Mutations | Rebalance Execution Mutations | +|---------------|---------------------|----------------------------------------------------------------------------------------------------------------------| +| Uninitialized | ❌ None | ✅ Initial cache write (after first user request) | +| Initialized | ❌ None | ❌ Not active | +| Rebalancing | ❌ None | ✅ All cache mutations (expand, trim, write to cache/LastRequested/NoRebalanceRange)
⚠️ MUST yield on cancellation | + +### Mutation Rules Summary + +**User Path mutations (Invariant 8 - NEW):** +- ❌ **NONE** - User Path is read-only with respect to cache state +- User Path NEVER calls `Cache.Rematerialize()` +- User Path NEVER writes to `LastRequested` +- User Path NEVER writes to `NoRebalanceRange` + +**Rebalance Execution mutations (Invariant 36, 36a):** +1. Uses delivered data from intent as authoritative base +2. Expanding to `DesiredCacheRange` (fetch only truly missing ranges) +3. Trimming excess data outside `DesiredCacheRange` +4. Writing to `Cache.Rematerialize()` (cache data and range) +5. Writing to `LastRequested` +6. Recomputing and writing to `NoRebalanceRange` + +**Single-Writer Architecture (Invariant -1):** +- User Path **NEVER** mutates cache (read-only) +- Rebalance Execution is the **SOLE WRITER** of all cache state +- User Path **cancels rebalance** to prevent interference (priority via cancellation) +- Rebalance Execution **MUST yield** immediately on cancellation (Invariant 34a) +- No race conditions possible (single-writer eliminates mutation conflicts) + +--- + +## Concurrency Semantics + +### Cancellation Protocol + +User Path has priority but does NOT mutate cache: + +1. **Pre-operation cancellation:** User Path cancels active rebalance +2. **Read/fetch:** User Path reads from cache or fetches from IDataSource (NO mutation) +3. **Immediate return:** User Path returns data to user (never waits) +4. **Intent publication:** User Path emits intent with delivered data +5. **Rebalance yields:** Background rebalance stops if cancelled +6. **New rebalance:** New intent triggers new rebalance execution with new delivered data + +### Cancellation Guarantees (Invariants 34, 34a, 34b) + +- Rebalance Execution **MUST support cancellation** at all stages +- Rebalance Execution **MUST yield** to User Path immediately +- Cancelled execution **MUST NOT leave cache inconsistent** + +### State Safety + +- **Atomicity:** All cache mutations are atomic (Invariant 12) +- **Consistency:** `CacheData ↔ CurrentCacheRange` always consistent (Invariant 11) +- **Contiguity:** Cache data never contains gaps (Invariant 9a) +- **Idempotence:** Multiple cancellations are safe + +--- + +## State Invariants by State + +### In Uninitialized State: +- ✅ All range and data fields are null +- ✅ User Path is read-only (no mutations) +- ✅ Rebalance Execution is not active (will activate after first user request) + +### In Initialized State: +- ✅ `CacheData ↔ CurrentCacheRange` consistent (Invariant 11) +- ✅ Cache is contiguous (Invariant 9a) +- ✅ User Path is read-only (Invariant 8 - NEW) +- ✅ Rebalance Execution is not active + +### In Rebalancing State: +- ✅ `CacheData ↔ CurrentCacheRange` remain consistent (Invariant 11) +- ✅ Cache is contiguous (Invariant 9a) +- ✅ User Path may cancel but NOT mutate (Invariants 0, 0a) +- ✅ Rebalance Execution is active and sole writer (Invariant 36) +- ✅ Rebalance Execution is cancellable (Invariant 34) +- ✅ **Single-writer architecture** (no race conditions) + +--- + +## Examples + +### Example 1: Cold Start → Initialized +``` +State: Uninitialized +User requests [100, 200] +→ User Path fetches [100, 200] from IDataSource +→ User Path returns data to user immediately +→ User Path publishes intent with delivered data +→ Rebalance Execution writes to cache (first cache write) +→ Sets CacheData, CurrentCacheRange, LastRequested +→ Triggers rebalance (fire-and-forget) +State: Initialized +``` + +### Example 2: Expansion During Rebalancing +``` +State: Initialized +CurrentCacheRange = [100, 200] + +User requests [150, 250] +→ User Path reads [150, 200] from cache, fetches [200, 250] from IDataSource +→ User Path returns assembled data to user +→ User Path publishes intent with delivered data [150, 250] +→ Triggers rebalance R1 for DesiredCacheRange = [50, 300] +State: Rebalancing (R1 executing in background) + +User requests [200, 300] (before R1 completes) +→ CANCELS R1 (Invariant 0a - User Path priority) +→ User Path reads/fetches data (NO cache mutation) +→ User Path returns data [200, 300] to user +→ User Path publishes new intent with delivered data [200, 300] +→ Triggers rebalance R2 for new DesiredCacheRange +State: Rebalancing (R2 executing) +``` + +### Example 3: Full Cache Miss During Rebalancing +``` +State: Rebalancing +CurrentCacheRange = [100, 200] +Rebalance R1 executing for DesiredCacheRange = [50, 250] + +User requests [500, 600] (no intersection) +→ CANCELS R1 (Invariant 0a - User Path priority) +→ User Path fetches [500, 600] from IDataSource (cache miss) +→ User Path returns data to user +→ User Path publishes intent with delivered data [500, 600] +→ Triggers rebalance R2 for new DesiredCacheRange = [450, 650] +State: Rebalancing (R2 executing - will eventually replace cache) +``` + +--- + +## Architectural Summary + +This state machine enforces three critical architectural constraints: + +1. **Single-Writer Architecture:** Only Rebalance Execution mutates cache state (Invariant 36) +2. **User Path Read-Only:** User Path never mutates cache, LastRequested, or NoRebalanceRange (Invariant 8) +3. **User Priority via Cancellation:** User requests cancel rebalance to prevent interference, not for mutation exclusion (Invariants 0, 0a) + +The state machine guarantees: +- Fast, non-blocking user access (Invariants 1, 2) +- Eventual convergence to optimal cache shape (Invariant 23) +- Atomic, consistent cache state (Invariants 11, 12) +- No race conditions (single-writer eliminates mutation conflicts) +- Safe cancellation at any time (Invariants 34, 34a, 34b) \ No newline at end of file diff --git a/docs/component-map.md b/docs/component-map.md new file mode 100644 index 0000000..1c0f964 --- /dev/null +++ b/docs/component-map.md @@ -0,0 +1,1772 @@ +# Sliding Window Cache - Complete Component Map + +## Document Purpose + +This document provides a comprehensive map of all components in the Sliding Window Cache, including: +- Component types (value/reference types) +- Ownership relationships +- Read/write patterns +- Data flow diagrams +- Thread safety model + +**Last Updated**: February 8, 2026 + +--- + +## Table of Contents + +1. [Component Statistics](#component-statistics) +2. [Component Type Legend](#component-type-legend) +3. [Component Hierarchy](#component-hierarchy) +4. [Detailed Component Catalog](#detailed-component-catalog) +5. [Ownership & Data Flow Diagram](#ownership--data-flow-diagram) +6. [Read/Write Patterns](#readwrite-patterns) +7. [Thread Safety Model](#thread-safety-model) +8. [Type Summary Tables](#type-summary-tables) + +--- + +## Component Statistics + +**Total Components**: 19 files in the codebase + +**By Type**: +- 🟦 **Classes (Reference Types)**: 10 +- 🟩 **Structs (Value Types)**: 3 +- 🟧 **Interfaces**: 2 +- 🟪 **Enums**: 1 +- 🟨 **Records**: 2 + +**By Mutability**: +- **Immutable**: 12 components +- **Mutable**: 5 components (CacheState, IntentManager._currentIntentCts, Storage implementations) + +**By Execution Context**: +- **User Thread**: 1 (UserRequestHandler) +- **Background / ThreadPool**: 4 (Scheduler, DecisionEngine, Executor, + async parts of IntentManager) +- **Both Contexts**: 1 (CacheDataFetcher) +- **Neutral**: 13 (configuration, data structures, interfaces) + +**Shared Mutable State**: +- **CacheState** (shared by UserRequestHandler, RebalanceExecutor, DecisionEngine) +- No other shared mutable state + +**External Dependencies**: +- **IDataSource** (user-provided implementation) +- **TDomain** (from Intervals.NET library) + +--- + +## Component Type Legend + +- **🟦 CLASS** = Reference type (heap-allocated, passed by reference) +- **🟩 STRUCT** = Value type (stack-allocated or inline, passed by value) +- **🟧 INTERFACE** = Contract definition +- **🟪 ENUM** = Value type enumeration +- **🟨 RECORD** = Reference type with value semantics + +**Ownership Arrows**: +- `owns →` = Component owns/contains the other +- `reads ⊳` = Component reads from the other +- `writes ⊲` = Component writes to the other +- `uses ◇` = Component uses/depends on the other + +**Mutability Indicators**: +- ✏️ = Mutable field/property +- 🔒 = Readonly/immutable +- ⚠️ = Mutable shared state (requires coordination) + +--- + +## Component Hierarchy + +### Public API Layer + +``` +🟦 WindowCache [Public Facade] +│ +├── owns → 🟦 UserRequestHandler +│ +└── composes (at construction): + ├── 🟦 CacheState ⚠️ Shared Mutable + ├── 🟦 IntentController + │ └── owns → 🟦 RebalanceScheduler + ├── 🟦 RebalanceDecisionEngine + │ ├── owns → 🟩 ThresholdRebalancePolicy + │ └── owns → 🟩 ProportionalRangePlanner + ├── 🟦 RebalanceExecutor + └── 🟦 CacheDataExtensionService + └── uses → 🟧 IDataSource (user-provided) +``` + +--- + +## Detailed Component Catalog + +### 1. Configuration & Data Transfer Types + +#### 🟨 WindowCacheOptions +```csharp +public record WindowCacheOptions +``` + +**File**: `src/SlidingWindowCache/Configuration/WindowCacheOptions.cs` + +**Type**: Record (reference type with value semantics) + +**Properties** (all readonly): +- `double LeftCacheSize` - Coefficient for left cache size (≥0) +- `double RightCacheSize` - Coefficient for right cache size (≥0) +- `double? LeftThreshold` - Left rebalance threshold percentage (optional, ≥0) +- `double? RightThreshold` - Right rebalance threshold percentage (optional, ≥0) +- `TimeSpan DebounceDelay` - Debounce delay for rebalance operations (default: 100ms) +- `UserCacheReadMode ReadMode` - Cache read strategy (Snapshot or CopyOnRead) + +**Ownership**: Created by user, passed to WindowCache constructor + +**Mutability**: Immutable (init-only properties) + +**Lifetime**: Lives as long as cache instance + +**Used by**: +- WindowCache (constructor) +- ThresholdRebalancePolicy (threshold configuration) +- ProportionalRangePlanner (size configuration) + +--- + +#### 🟪 UserCacheReadMode +```csharp +public enum UserCacheReadMode +``` + +**File**: `src/SlidingWindowCache/UserCacheReadMode.cs` + +**Type**: Enum (value type) + +**Values**: +- `Snapshot` - Zero-allocation reads, expensive rebalance (uses array) +- `CopyOnRead` - Allocation on reads, cheap rebalance (uses List) + +**Ownership**: Part of WindowCacheOptions + +**Mutability**: Immutable + +**Used by**: +- WindowCacheOptions +- ICacheStorage implementations (determines storage strategy) + +**Trade-offs**: +- **Snapshot**: Fast reads, slow rebalance, LOH pressure for large caches +- **CopyOnRead**: Slow reads, fast rebalance, better memory pressure + +--- + +#### 🟧 IDataSource +```csharp +public interface IDataSource + where TRangeType : IComparable +``` + +**File**: `src/SlidingWindowCache/IDataSource.cs` + +**Type**: Interface (contract) + +**Methods**: +- `Task> FetchAsync(Range range, CancellationToken ct)` + - Required: Fetch data for a single range +- `Task>> FetchAsync(IEnumerable> ranges, CancellationToken ct)` + - Optional override: Batch fetch optimization + +**Ownership**: User provides implementation + +**Used by**: CacheDataExtensionService (calls to fetch external data) + +**Operations**: Read-only (fetches external data) + +**Characteristics**: +- User-implemented +- May perform I/O (network, disk, database) +- Should respect CancellationToken +- Default batch implementation uses parallel fetch + +--- + +#### 🟨 RangeChunk +```csharp +public record RangeChunk(Range Range, IEnumerable Data) + where TRangeType : IComparable +``` + +**File**: `src/SlidingWindowCache/DTO/RangeChunk.cs` + +**Type**: Record (reference type, immutable) + +**Properties**: +- `Range Range` - The range covered by this chunk +- `IEnumerable Data` - The data for this range + +**Ownership**: Created by IDataSource, consumed by CacheDataExtensionService + +**Mutability**: Immutable + +**Lifetime**: Temporary (method return value) + +**Purpose**: Encapsulates data fetched for a particular range (batch fetch result) + +--- + +### 2. Storage Layer + +#### 🟧 ICacheStorage +```csharp +internal interface ICacheStorage + where TRange : IComparable + where TDomain : IRangeDomain +``` + +**File**: `src/SlidingWindowCache/Storage/ICacheStorage.cs` + +**Type**: Interface (internal) + +**Properties**: +- `UserCacheReadMode Mode { get; }` - The read mode this strategy implements +- `Range Range { get; }` - Current range of cached data + +**Methods**: +- `void Rematerialize(RangeData rangeData)` ⊲ **WRITE** + - Replaces internal storage with new range data + - Called during cache initialization and rebalancing +- `ReadOnlyMemory Read(Range range)` ⊳ **READ** + - Returns data for the specified range + - Behavior varies by implementation (zero-copy vs. copy) +- `RangeData ToRangeData()` ⊳ **READ** + - Converts current state to RangeData representation + +**Implementations**: +- `SnapshotReadStorage` +- `CopyOnReadStorage` + +**Owned by**: CacheState + +**Writers**: UserRequestHandler, RebalanceExecutor (via CacheState) + +**Readers**: UserRequestHandler, RebalanceExecutor + +--- + +#### 🟦 SnapshotReadStorage +```csharp +internal sealed class SnapshotReadStorage : ICacheStorage +``` + +**File**: `src/SlidingWindowCache/Storage/SnapshotReadStorage.cs` + +**Type**: Class (sealed) + +**Fields**: +- `TDomain _domain` (readonly) - Domain for range calculations +- ✏️ `TData[] _storage` - Mutable array holding cached data +- ✏️ `Range Range` (property) - Current cache range + +**Operations**: +- `Rematerialize()` ⊲ **WRITE** + - Allocates new array + - Replaces `_storage` completely + - Updates `Range` +- `Read()` ⊳ **READ** + - Returns `ReadOnlyMemory` view over internal array + - **Zero allocation** (slice of existing array) +- `ToRangeData()` ⊳ **READ** + - Creates RangeData from current array + +**Characteristics**: +- ✅ Zero-allocation reads (fast) +- ❌ Expensive rebalance (always allocates new array) +- ⚠️ Large arrays may end up on LOH (≥85KB) + +**Ownership**: Owned by CacheState (single instance) + +**Internal State**: `TData[]` array (mutable, replaced atomically) + +**Thread Safety**: Not thread-safe (single consumer model) + +**Best for**: Read-heavy workloads, predictable memory patterns + +--- + +#### 🟦 CopyOnReadStorage +```csharp +internal sealed class CopyOnReadStorage : ICacheStorage +``` + +**File**: `src/SlidingWindowCache/Storage/CopyOnReadStorage.cs` + +**Type**: Class (sealed) + +**Fields**: +- `TDomain _domain` (readonly) - Domain for range calculations +- ✏️ `List _activeStorage` - Active storage (immutable during reads) +- ✏️ `List _stagingBuffer` - Staging buffer (write-only during rematerialization) +- ✏️ `Range Range` (property) - Current cache range + +**Staging Buffer Pattern**: +- Two internal buffers: active storage + staging buffer +- Active storage never mutated during enumeration +- Staging buffer cleared, filled, then swapped with active +- Buffers may grow but never shrink (capacity reuse) + +**Operations**: +- `Rematerialize()` ⊲ **WRITE** + - Clears staging buffer (preserves capacity) + - Enumerates range data into staging (single-pass) + - Atomically swaps staging ↔ active + - Updates `Range` +- `Read()` ⊳ **READ** + - Allocates new `TData[]` array + - Copies from active storage + - Returns as `ReadOnlyMemory` +- `ToRangeData()` ⊳ **READ** + - Returns lazy enumerable over active storage + - Safe because active storage is immutable during reads + +**Characteristics**: +- ✅ Cheap rematerialization (amortized O(1) when capacity sufficient) +- ❌ Expensive reads (allocates + copies) +- ✅ Correct enumeration (staging buffer prevents corruption) +- ✅ No LOH pressure (List growth strategy) +- ✅ Satisfies Invariants A.3.8, A.3.9a, B.11-12 + +**Ownership**: Owned by CacheState (single instance) + +**Internal State**: Two `List` (swapped atomically) + +**Thread Safety**: Not thread-safe (single consumer model) + +**Best for**: Rematerialization-heavy workloads, large sliding windows, background cache layers + +**See**: [Storage Strategies Guide](storage-strategies.md) for detailed comparison and usage scenarios + +--- + +### 3. Diagnostics Infrastructure + +#### 🟧 ICacheDiagnostics +```csharp +public interface ICacheDiagnostics +``` + +**File**: `src/SlidingWindowCache/Infrastructure/Instrumentation/ICacheDiagnostics.cs` + +**Type**: Interface (public) + +**Purpose**: Optional observability and instrumentation for cache behavioral events + +**Methods** (15 event recording methods): + +**User Path Events:** +- `void UserRequestServed()` - Records completed user request +- `void CacheExpanded()` - Records cache expansion (partial hit optimization) +- `void CacheReplaced()` - Records cache replacement (non-intersecting jump) +- `void UserRequestFullCacheHit()` - Records full cache hit (optimal path) +- `void UserRequestPartialCacheHit()` - Records partial cache hit with extension +- `void UserRequestFullCacheMiss()` - Records full cache miss (cold start or jump) + +**Data Source Access Events:** +- `void DataSourceFetchSingleRange()` - Records single-range fetch from IDataSource +- `void DataSourceFetchMissingSegments()` - Records multi-segment fetch (gap filling) + +**Rebalance Intent Lifecycle Events:** +- `void RebalanceIntentPublished()` - Records intent publication by User Path +- `void RebalanceIntentCancelled()` - Records intent cancellation before/during execution + +**Rebalance Execution Lifecycle Events:** +- `void RebalanceExecutionStarted()` - Records execution start after decision approval +- `void RebalanceExecutionCompleted()` - Records successful execution completion +- `void RebalanceExecutionCancelled()` - Records execution cancellation mid-flight + +**Rebalance Skip Optimization Events:** +- `void RebalanceSkippedNoRebalanceRange()` - Records skip due to NoRebalanceRange policy +- `void RebalanceSkippedSameRange()` - Records skip due to same-range optimization + +**Implementations**: +- `EventCounterCacheDiagnostics` - Default counter-based implementation +- `NoOpDiagnostics` - Zero-cost no-op implementation (default) + +**Usage**: Passed to WindowCache constructor as optional parameter + +**Ownership**: User creates instance (optional), passed by reference to all actors + +**Integration Points**: +- All actors receive diagnostics instance via constructor injection +- Events recorded at key behavioral points throughout cache lifecycle + +**Zero-Cost Design**: When not provided, `NoOpDiagnostics` is used with empty methods that JIT optimizes away + +**See**: [Diagnostics Guide](diagnostics.md) for comprehensive usage documentation + +--- + +#### 🟦 EventCounterCacheDiagnostics +```csharp +public class EventCounterCacheDiagnostics : ICacheDiagnostics +``` + +**File**: `src/SlidingWindowCache/Infrastructure/Instrumentation/DefaultCacheDiagnostics.cs` + +**Type**: Class (public, thread-safe) + +**Purpose**: Default thread-safe implementation using atomic counters + +**Fields** (15 private int counters): +- `_userRequestServed`, `_cacheExpanded`, `_cacheReplaced` +- `_userRequestFullCacheHit`, `_userRequestPartialCacheHit`, `_userRequestFullCacheMiss` +- `_dataSourceFetchSingleRange`, `_dataSourceFetchMissingSegments` +- `_rebalanceIntentPublished`, `_rebalanceIntentCancelled` +- `_rebalanceExecutionStarted`, `_rebalanceExecutionCompleted`, `_rebalanceExecutionCancelled` +- `_rebalanceSkippedNoRebalanceRange`, `_rebalanceSkippedSameRange` + +**Properties**: 15 read-only properties exposing counter values + +**Methods**: +- 15 event recording methods (explicit interface implementation) + - All use `Interlocked.Increment` for thread-safety + - ~1-5 nanoseconds per event +- `void Reset()` - Resets all counters to zero (for test isolation) + +**Characteristics**: +- ✅ Thread-safe (atomic operations, no locks) +- ✅ Low overhead (~60 bytes memory, <5ns per event) +- ✅ Instance-based (multiple caches can have separate diagnostics) +- ✅ Observable state for testing and monitoring + +**Use Cases**: +- Testing and validation (primary use case) +- Development debugging +- Production monitoring (optional) + +**Thread Safety**: Thread-safe via `Interlocked.Increment` + +**Lifetime**: Typically matches cache lifetime + +**See**: [Diagnostics Guide](diagnostics.md) for complete API reference and examples + +--- + +#### 🟦 NoOpDiagnostics +```csharp +public class NoOpDiagnostics : ICacheDiagnostics +``` + +**File**: `src/SlidingWindowCache/Infrastructure/Instrumentation/NoOpDiagnostics.cs` + +**Type**: Class (public, singleton-compatible) + +**Purpose**: Zero-overhead no-op implementation for production use + +**Methods**: All 15 interface methods implemented as empty method bodies + +**Characteristics**: +- ✅ **Absolute zero overhead** - empty methods inlined/eliminated by JIT +- ✅ No state (0 bytes memory) +- ✅ No allocations +- ✅ No performance impact + +**Usage**: Automatically used when `cacheDiagnostics` parameter is `null` (default) + +**Design Rationale**: +- Enables diagnostics API without forcing overhead when not needed +- JIT compiler optimizes away empty method calls completely +- Maintains clean API without conditional logic in hot paths + +**Thread Safety**: Stateless, inherently thread-safe + +**Lifetime**: Can be singleton or per-cache (doesn't matter - no state) + +--- + +### 4. State Management + +#### 🟦 CacheState +```csharp +internal sealed class CacheState + where TRange : IComparable + where TDomain : IRangeDomain +``` + +**File**: `src/SlidingWindowCache/CacheState.cs` + +**Type**: Class (sealed) + +**Properties** (all mutable): +- ✏️ `ICacheStorage Cache { get; }` - The actual cache storage +- ✏️ `Range? LastRequested { get; set; }` - Last requested range by user +- ✏️ `Range? NoRebalanceRange { get; set; }` - Range within which no rebalancing occurs +- 🔒 `TDomain Domain { get; }` - Domain for range calculations (readonly) + +**Ownership**: +- Created by WindowCache constructor +- **Shared by reference** across multiple components + +**Shared with** (read/write): +- **UserRequestHandler** ⊲⊳ + - Reads: `Cache.Range`, `Cache.Read()`, `Cache.ToRangeData()` + - Writes: `Cache.Rematerialize()`, `LastRequested` +- **RebalanceExecutor** ⊲⊳ + - Reads: `Cache.Range`, `Cache.ToRangeData()` + - Writes: `Cache.Rematerialize()`, `NoRebalanceRange` +- **RebalanceScheduler** ⊳ (via DecisionEngine) + - Reads: `NoRebalanceRange` + +**Characteristics**: +- ⚠️ **Mutable shared state** (central coordination point) +- ❌ **No internal locking** (single consumer model by design) +- ✅ **Atomic operations** (Rematerialize replaces storage atomically) + +**Thread Safety**: +- Not thread-safe (intentional) +- Coordination via CancellationToken +- User Path cancels rebalance before mutations + +**Role**: Central point for cache data and metadata + +--- + +### 5. User Path (Fast Path) + +#### 🟦 UserRequestHandler +```csharp +internal sealed class UserRequestHandler +``` + +**File**: `src/SlidingWindowCache/UserPath/UserRequestHandler.cs` + +**Type**: Class (sealed) + +**Fields** (all readonly): +- `CacheState _state` +- `CacheDataExtensionService _cacheExtensionService` +- `IntentController _intentManager` + +**Main Method**: +```csharp +public async ValueTask> HandleRequestAsync( + Range requestedRange, + CancellationToken cancellationToken) +``` + +**Operation Flow**: +1. **Cancel pending rebalance** - `_intentManager.CancelPendingRebalance()` +2. **Check cache coverage** - `_state.Cache.Range.Contains(requestedRange)` +3. **Extend if needed** - `_cacheFetcher.ExtendCacheAsync()` + `_state.Cache.Rematerialize()` +4. **Update metadata** - `_state.LastRequested = requestedRange` +5. **Trigger rebalance** - `_intentManager.PublishIntent(requestedRange)` (fire-and-forget) +6. **Return data** - `_state.Cache.Read(requestedRange)` + +**Reads from**: +- ⊳ `_state.Cache` (Range, Read, ToRangeData) + +**Writes to**: +- ⊲ `_state.Cache` (via Rematerialize - expands to cover requested range) +- ⊲ `_state.LastRequested` + +**Uses**: +- ◇ `_cacheFetcher` (to fetch missing data) +- ◇ `_intentManager` (PublishIntent, CancelPendingRebalance) + +**Characteristics**: +- ✅ Executes in **User Thread** (synchronous) +- ✅ Always serves user requests (never waits for rebalance) +- ✅ May expand cache to cover requested range +- ✅ Always triggers rebalance intent +- ❌ **Never** trims or normalizes cache +- ❌ **Never** invokes decision logic +- ❌ **Never** blocks on rebalance + +**Ownership**: Owned by WindowCache + +**Execution Context**: User Thread (synchronous) + +**Responsibilities**: Serve user requests fast, trigger rebalance intents + +**Invariants Enforced**: +- A.1-0a: Cancels rebalance before cache mutations +- 1: Always serves user requests +- 2: Never waits for rebalance execution +- 3: Sole source of rebalance intent +- 10: Always returns exactly RequestedRange + +--- + +### 5. Rebalance System - Intent Management + +#### 🟦 IntentController +```csharp +internal sealed class IntentController +``` + +**File**: `src/SlidingWindowCache/CacheRebalance/IntentController.cs` + +**Type**: Class (sealed) + +**Role**: Intent Controller (component 1 of 2 in Rebalance Intent Manager actor) + +**Fields**: +- `RebalanceScheduler _scheduler` (readonly) +- ✏️ `CancellationTokenSource? _currentIntentCts` - **Mutable**, tracks current intent + +**Key Methods**: + +**`PublishIntent(Range requestedRange)`**: +```csharp +public void PublishIntent(Range requestedRange) +{ + // 1. Invalidate previous intent + _currentIntentCts?.Cancel(); + _currentIntentCts?.Dispose(); + + // 2. Create new intent identity + _currentIntentCts = new CancellationTokenSource(); + var intentToken = _currentIntentCts.Token; + + // 3. Delegate to scheduler + _scheduler.ScheduleRebalance(requestedRange, intentToken); +} +``` + +**`CancelPendingRebalance()`**: +```csharp +public void CancelPendingRebalance() +{ + if (_currentIntentCts != null) + { + _currentIntentCts.Cancel(); + _currentIntentCts.Dispose(); + _currentIntentCts = null; + } +} +``` + +**`WaitForIdleAsync(TimeSpan? timeout = null)`** (Infrastructure/Testing): +```csharp +public Task WaitForIdleAsync(TimeSpan? timeout = null) +{ + // Delegate to RebalanceScheduler's Task tracking mechanism + return _scheduler.WaitForIdleAsync(timeout); +} +``` + +**Characteristics**: +- ✅ Owns intent identity (CancellationTokenSource lifecycle) +- ✅ Single-flight enforcement (only one active intent) +- ✅ Exposes cancellation to User Path +- ✅ **Lock-free implementation** using `Interlocked.Exchange` for atomic operations +- ✅ **Thread-safe without locks** - no race conditions, tested under concurrent load +- ⚠️ **Intent does not guarantee execution** - execution is opportunistic +- ❌ **Does NOT**: Timing, scheduling, execution logic + +**Concurrency Model**: +- Uses lightweight synchronization primitives (`Interlocked.Exchange`) +- No locks, no `lock` statements, no mutexes +- Atomic field replacement ensures thread-safety +- Validated by `ConcurrencyStabilityTests` under concurrent load + +**Ownership**: +- Owned by WindowCache +- Composes with RebalanceScheduler + +**Execution Context**: +- Synchronous methods (called from User Thread) +- Scheduled work executes in Background + +**State**: +- `_currentIntentCts` (mutable, nullable) +- Represents identity of latest intent + +**Responsibilities**: +- Intent lifecycle management +- Cancellation coordination +- Identity versioning +- Idle synchronization proxy (delegates to RebalanceScheduler for testing infrastructure) + +**Invariants Enforced**: +- C.17: At most one active intent +- C.18: Previous intents become obsolete +- C.24: Intent does not guarantee execution + +--- + +#### 🟦 RebalanceScheduler +```csharp +internal sealed class RebalanceScheduler +``` + +**File**: `src/SlidingWindowCache/CacheRebalance/RebalanceScheduler.cs` + +**Type**: Class (sealed) + +**Role**: Execution Scheduler (component 2 of 2 in Rebalance Intent Manager actor) + +**Fields** (all readonly): +- `CacheState _state` +- `RebalanceDecisionEngine _decisionEngine` +- `RebalanceExecutor _executor` +- `TimeSpan _debounceDelay` +- `Task _idleTask` - Tracks latest background Task for deterministic synchronization + +**Key Methods**: + +**`ScheduleRebalance(RangeData deliveredData, CancellationToken intentToken)`**: +```csharp +public void ScheduleRebalance(Range requestedRange, CancellationToken intentToken) +{ + // Fire-and-forget: schedule execution in background thread pool + Task.Run(async () => + { + try + { + // Debounce delay + await Task.Delay(_debounceDelay, intentToken); + + // Intent validity check + if (intentToken.IsCancellationRequested) + return; + + // Execute pipeline + await ExecutePipelineAsync(requestedRange, intentToken); + } + catch (OperationCanceledException) + { + // Expected when intent is cancelled + } + }, intentToken); +} +``` + +**`ExecutePipelineAsync(Range requestedRange, CancellationToken cancellationToken)`** (private): +```csharp +private async Task ExecutePipelineAsync(...) +{ + // Final cancellation check + if (cancellationToken.IsCancellationRequested) + return; + + // Step 1: Decision logic + var decision = _decisionEngine.ShouldExecuteRebalance( + requestedRange, _state.NoRebalanceRange); + + // Step 2: If skip, return early + if (!decision.ShouldExecute) + return; + + // Step 3: Execute if allowed + await _executor.ExecuteAsync(decision.DesiredRange!.Value, cancellationToken); +} +``` + +**`WaitForIdleAsync(TimeSpan? timeout = null)`** (Infrastructure/Testing): +```csharp +public async Task WaitForIdleAsync(TimeSpan? timeout = null) +{ + // Observe-and-stabilize pattern (all builds) + // 1. Volatile.Read(_idleTask) → observe current Task + // 2. await observedTask → wait for completion + // 3. Re-check if _idleTask changed → detect new rebalance + // 4. Loop until Task reference stabilizes +} +``` + +**Characteristics**: +- ✅ Executes in **Background / ThreadPool** +- ✅ Handles debounce delay +- ✅ Orchestrates Decision → Execution pipeline +- ✅ Checks intent validity before execution +- ✅ Ensures single-flight through cancellation +- ❌ **Does NOT**: Intent identity, cancellation management + +**Ownership**: Owned by IntentController + +**Execution Context**: Background / ThreadPool + +**State**: Stateless (only readonly fields, plus `_idleTask` field for deterministic synchronization) + +**Important Design Note**: RebalanceScheduler is intentionally stateless and does not own intent identity. +All intent lifecycle, superseding, and cancellation semantics are delegated to the Intent Controller (IntentController). +The scheduler receives a CancellationToken for each execution and simply checks its validity. + +**Responsibilities**: +- Timing and debounce delay +- Pipeline orchestration (Decision → Execution) +- Validity checking before execution starts +- Task lifecycle tracking for deterministic synchronization (infrastructure/testing) + +**Invariants Enforced**: +- C.20: Obsolete intents don't start execution +- C.21: At most one execution active (via cancellation) + +--- + +### 6. Rebalance System - Decision & Policy + +#### 🟦 RebalanceDecisionEngine +```csharp +internal sealed class RebalanceDecisionEngine +``` + +**File**: `src/SlidingWindowCache/CacheRebalance/RebalanceDecisionEngine.cs` + +**Type**: Class (sealed) + +**Role**: Pure Decision Logic + +**Fields** (all readonly, value types): +- `ThresholdRebalancePolicy _policy` (struct, copied) +- `ProportionalRangePlanner _planner` (struct, copied) + +**Key Method**: +```csharp +public RebalanceDecision ShouldExecuteRebalance( + Range requestedRange, + Range? noRebalanceRange) +{ + // Decision Path D1: Check NoRebalanceRange (fast path) + if (noRebalanceRange.HasValue && + !_policy.ShouldRebalance(noRebalanceRange.Value, requestedRange)) + { + return RebalanceDecision.Skip(); + } + + // Decision Path D2/D3: Compute DesiredCacheRange + var desiredRange = _planner.Plan(requestedRange); + + return RebalanceDecision.Execute(desiredRange); +} +``` + +**Characteristics**: +- ✅ **Pure function** (no side effects) +- ✅ **Deterministic** (same inputs → same outputs) +- ✅ **Stateless** (composes value-type policies) +- ✅ Invoked only in background +- ❌ Not visible to User Path + +**Uses**: +- ◇ `_policy.ShouldRebalance()` - check NoRebalanceRange containment +- ◇ `_planner.Plan()` - compute DesiredCacheRange + +**Returns**: `RebalanceDecision` (struct) + +**Ownership**: Owned by WindowCache, used by RebalanceScheduler + +**Execution Context**: Background / ThreadPool + +**Responsibilities**: +- Evaluate if rebalance is needed +- Check NoRebalanceRange +- Compute DesiredCacheRange + +**Invariants Enforced**: +- 24: Decision path is purely analytical +- 25: Never mutates cache state +- 26: No rebalance if inside NoRebalanceRange +- 27: No rebalance if DesiredCacheRange == CurrentCacheRange + +--- + +#### 🟩 ThresholdRebalancePolicy +```csharp +internal readonly struct ThresholdRebalancePolicy +``` + +**File**: `src/SlidingWindowCache/CacheRebalance/Policy/ThresholdRebalancePolicy.cs` + +**Type**: Struct (readonly value type) + +**Role**: Cache Geometry Policy - Threshold Rules (component 1 of 2) + +**Fields** (all readonly): +- `WindowCacheOptions _options` +- `TDomain _domain` + +**Key Methods**: + +**`ShouldRebalance(Range noRebalanceRange, Range requested)`**: +```csharp +public bool ShouldRebalance(Range noRebalanceRange, Range requested) + => !noRebalanceRange.Contains(requested); +``` + +**`GetNoRebalanceRange(Range cacheRange)`**: +```csharp +public Range? GetNoRebalanceRange(Range cacheRange) + => cacheRange.ExpandByRatio( + domain: _domain, + leftRatio: -(_options.LeftThreshold ?? 0), // Negate to shrink + rightRatio: -(_options.RightThreshold ?? 0) // Negate to shrink + ); +``` + +**Characteristics**: +- ✅ **Value type** (struct, passed by value) +- ✅ **Pure functions** (no state mutation) +- ✅ **Configuration-driven** (uses WindowCacheOptions) +- ✅ **Stateless** (readonly fields) + +**Ownership**: Value type, copied into RebalanceDecisionEngine and RebalanceExecutor + +**Execution Context**: Background / ThreadPool + +**Responsibilities**: +- Compute NoRebalanceRange (shrinks cache by threshold ratios) +- Check if requested range falls outside no-rebalance zone +- Answers: **"When to rebalance"** + +**Invariants Enforced**: +- 26: No rebalance if inside NoRebalanceRange +- 33: NoRebalanceRange derived from CurrentCacheRange + config + +--- + +#### 🟩 ProportionalRangePlanner +```csharp +internal readonly struct ProportionalRangePlanner +``` + +**File**: `src/SlidingWindowCache/DesiredRangePlanner/ProportionalRangePlanner.cs` + +**Type**: Struct (readonly value type) + +**Role**: Cache Geometry Policy - Shape Planning (component 2 of 2) + +**Fields** (all readonly): +- `WindowCacheOptions _options` +- `TDomain _domain` + +**Key Method**: +```csharp +public Range Plan(Range requested) +{ + var size = requested.Span(_domain); + + var left = size.Value * _options.LeftCacheSize; + var right = size.Value * _options.RightCacheSize; + + return requested.Expand( + domain: _domain, + left: (long)left, + right: (long)right + ); +} +``` + +**Characteristics**: +- ✅ **Value type** (struct, passed by value) +- ✅ **Pure function** (no state) +- ✅ **Configuration-driven** (uses WindowCacheOptions) +- ✅ **Independent of current cache contents** +- ✅ **Stateless** (readonly fields) + +**Ownership**: Value type, copied into RebalanceDecisionEngine + +**Execution Context**: Background / ThreadPool + +**Responsibilities**: +- Compute DesiredCacheRange (expands requested by left/right coefficients) +- Define canonical cache geometry +- Answers: **"What shape to target"** + +**Invariants Enforced**: +- 29: DesiredCacheRange computed from RequestedRange + config +- 30: Independent of current cache contents +- 31: Canonical target cache state +- 32: Sliding window geometry defined by configuration + +--- + +#### 🟩 RebalanceDecision +```csharp +internal readonly struct RebalanceDecision + where TRange : IComparable +``` + +**File**: `src/SlidingWindowCache/CacheRebalance/RebalanceDecision.cs` + +**Type**: Struct (readonly value type) + +**Properties** (all readonly): +- `bool ShouldExecute` - Whether rebalance should proceed +- `Range? DesiredRange` - Target cache range (if executing) + +**Factory Methods**: +- `static Skip()` → Returns decision to skip rebalance +- `static Execute(Range desiredRange)` → Returns decision to execute with target range + +**Characteristics**: +- ✅ **Value type** (struct) +- ✅ **Immutable** +- ✅ Represents decision outcome + +**Ownership**: Created by RebalanceDecisionEngine, consumed by RebalanceScheduler + +**Mutability**: Immutable + +**Lifetime**: Temporary (local variable in pipeline) + +**Purpose**: Encapsulates decision result (skip or execute with target range) + +--- + +### 7. Rebalance System - Execution + +#### 🟦 RebalanceExecutor +```csharp +internal sealed class RebalanceExecutor +``` + +**File**: `src/SlidingWindowCache/CacheRebalance/Executor/RebalanceExecutor.cs` + +**Type**: Class (sealed) + +**Role**: Mutating Actor (sole component responsible for cache normalization) + +**Fields** (all readonly): +- `CacheState _state` +- `CacheDataExtensionService _cacheExtensionService` +- `ThresholdRebalancePolicy _rebalancePolicy` + +**Key Method**: +```csharp +public async Task ExecuteAsync(Range desiredRange, CancellationToken cancellationToken) +{ + // Get current cache snapshot + var rangeData = _state.Cache.ToRangeData(); + + // Check if already at desired state (Decision Path D2) + if (rangeData.Range == desiredRange) + return; + + // Cancellation check before I/O + cancellationToken.ThrowIfCancellationRequested(); + + // Phase 1: Extend cache to cover desired range + var extended = await _cacheFetcher.ExtendCacheAsync(rangeData, desiredRange, cancellationToken); + + // Cancellation check after I/O + cancellationToken.ThrowIfCancellationRequested(); + + // Phase 2: Trim to desired range + var rebalanced = extended[desiredRange]; + + // Cancellation check before mutation + cancellationToken.ThrowIfCancellationRequested(); + + // Phase 3: Update cache (atomic mutation) + _state.Cache.Rematerialize(rebalanced); + + // Phase 4: Update no-rebalance range + _state.NoRebalanceRange = _rebalancePolicy.GetNoRebalanceRange(_state.Cache.Range); +} +``` + +**Reads from**: +- ⊳ `_state.Cache` (ToRangeData, Range) + +**Writes to**: +- ⊲ `_state.Cache` (via Rematerialize - normalizes to DesiredCacheRange) +- ⊲ `_state.NoRebalanceRange` + +**Uses**: +- ◇ `_cacheFetcher.ExtendCacheAsync()` (fetch missing data) +- ◇ `_rebalancePolicy.GetNoRebalanceRange()` (compute new threshold zone) + +**Characteristics**: +- ✅ Executes in **Background / ThreadPool** +- ✅ **Asynchronous** (performs I/O operations) +- ✅ **Cancellable** (checks token at multiple points) +- ✅ **Sole component** responsible for cache normalization +- ✅ Expands to DesiredCacheRange +- ✅ Trims excess data +- ✅ Updates NoRebalanceRange + +**Ownership**: Owned by WindowCache, used by RebalanceScheduler + +**Execution Context**: Background / ThreadPool + +**Operations**: Mutates cache atomically (expand, trim, update metadata) + +**Invariants Enforced**: +- 4: Rebalance is asynchronous +- 34: Supports cancellation at all stages +- 34a: Yields to User Path immediately upon cancellation +- 34b: Cancelled execution doesn't corrupt state +- 35: Only path responsible for cache normalization +- 35a: Mutates only for normalization (expand, trim, recompute NoRebalanceRange) +- 39-41: Upon completion, cache matches DesiredCacheRange + +--- + +#### 🟦 CacheDataExtensionService +```csharp +internal sealed class CacheDataExtensionService +``` + +**File**: `src/SlidingWindowCache/Core/Rebalance/Execution/CacheDataExtensionService.cs` + +**Type**: Class (sealed) + +**Role**: Data Fetcher (used by both User Path and Rebalance Path) + +**Fields** (all readonly): +- `IDataSource _dataSource` (user-provided) +- `TDomain _domain` + +**Key Method**: +```csharp +public async Task> ExtendCacheAsync( + RangeData current, + Range requested, + CancellationToken ct) +{ + // Step 1: Calculate missing ranges + var missingRanges = CalculateMissingRanges(current.Range, requested); + + // Step 2: Fetch missing data from data source + var fetchedResults = await _dataSource.FetchAsync(missingRanges, ct); + + // Step 3: Union fetched data with current cache + return UnionAll(current, fetchedResults, _domain); +} +``` + +**Uses**: +- ◇ `_dataSource.FetchAsync()` - external I/O to fetch data + +**Characteristics**: +- ✅ Calls external IDataSource +- ✅ Performs I/O operations +- ✅ Merges data **without trimming** +- ✅ Optimizes partial cache hits (only fetches missing ranges) +- ✅ **Shared by both paths** + +**Ownership**: Owned by WindowCache, shared by UserRequestHandler and RebalanceExecutor + +**Execution Context**: +- User Thread (when called by UserRequestHandler) +- Background / ThreadPool (when called by RebalanceExecutor) + +**External Dependencies**: IDataSource (user-provided) + +**Operations**: +- Fetches missing data +- Merges with existing cache +- **Never trims** + +**Shared by**: +- UserRequestHandler (expand to cover requested range) +- RebalanceExecutor (expand to cover desired range) + +--- + +### 8. Public Facade + +#### 🟦 WindowCache +```csharp +public sealed class WindowCache : IWindowCache +``` + +**File**: `src/SlidingWindowCache/WindowCache.cs` + +**Type**: Class (sealed, public) + +**Role**: Public Facade, Composition Root + +**Fields**: +- `UserRequestHandler _userRequestHandler` (readonly, private) +- `IntentController _intentController` (readonly, private) + +**Constructor**: Creates and wires all internal components: +```csharp +public WindowCache( + IDataSource dataSource, + TDomain domain, + WindowCacheOptions options) +{ + var cacheStorage = CreateCacheStorage(domain, options); + var state = new CacheState(cacheStorage, domain); + + var rebalancePolicy = new ThresholdRebalancePolicy(options, domain); + var rangePlanner = new ProportionalRangePlanner(options, domain); + var cacheFetcher = new CacheDataExtensionService(dataSource, domain, cacheDiagnostics); + + var decisionEngine = new RebalanceDecisionEngine(rebalancePolicy, rangePlanner); + var executor = new RebalanceExecutor(state, cacheFetcher, rebalancePolicy); + + _intentController = new IntentController( + state, decisionEngine, executor, options.DebounceDelay); + + _userRequestHandler = new UserRequestHandler( + state, cacheFetcher, _intentController); +} +``` + +**Public API**: +```csharp +// Primary domain API +public ValueTask> GetDataAsync( + Range requestedRange, + CancellationToken cancellationToken) +{ + return _userRequestHandler.HandleRequestAsync(requestedRange, cancellationToken); +} + +// Infrastructure API (Task tracking for synchronization) +public Task WaitForIdleAsync(TimeSpan? timeout = null) +{ + return _intentController.WaitForIdleAsync(timeout); +} +``` + +**Characteristics**: +- ✅ **Pure facade** (no business logic) +- ✅ **Composition root** (wires all components) +- ✅ **Public API** (single entry point) +- ✅ **Delegates everything** to UserRequestHandler + +**Ownership**: +- Owns all internal components +- Created by user +- Lives for application lifetime + +**Execution Context**: Neutral (just delegates) + +**Responsibilities**: +- Expose public API (GetDataAsync for domain operations) +- Expose testing infrastructure (WaitForIdleAsync for deterministic synchronization) +- Wire internal components together +- Own configuration and lifecycle + +**Does NOT**: +- Implement business logic +- Directly access cache state +- Perform decision logic + +--- + +## Ownership & Data Flow Diagram + +``` +┌─────────────────────────────────────────────────────────────────────┐ +│ USER (Consumer) │ +└─────────────────────────────────────────────────────────────────────┘ + │ + │ GetDataAsync(range, ct) + ▼ +┌─────────────────────────────────────────────────────────────────────┐ +│ WindowCache [Public Facade] │ +│ 🟦 CLASS (sealed, public) │ +│ │ +│ Constructor creates and wires: │ +│ ├─ 🟦 CacheState ──────────────────────────┐ (shared mutable) │ +│ ├─ 🟦 UserRequestHandler ──────────────────┼───┐ │ +│ ├─ 🟦 CacheDataExtensionService ───────────┼───┼───┐ │ +│ ├─ 🟦 RebalanceIntentManager ──────────────┼───┼───┼───┐ │ +│ │ └─ 🟦 RebalanceScheduler ──────────────┼───┼───┼───┼───┐ │ +│ ├─ 🟦 RebalanceDecisionEngine ─────────────┼───┼───┼───┼───┼───┐ │ +│ │ ├─ 🟩 ThresholdRebalancePolicy │ │ │ │ │ │ │ +│ │ └─ 🟩 ProportionalRangePlanner │ │ │ │ │ │ │ +│ └─ 🟦 RebalanceExecutor ────────────────────┼───┼───┼───┼───┼───┤ │ +│ │ │ │ │ │ │ │ +│ GetDataAsync() → delegates to UserRequestHandler │ +└────────────────────────────────────────────────┼───┼───┼───┼───┼───┼─┘ + │ │ │ │ │ │ + ═════════════════════════════════════════╪═══╪═══╪═══╪═══╪═══╪═ + USER THREAD │ │ │ │ │ │ + ═════════════════════════════════════════╪═══╪═══╪═══╪═══╪═══╪═ + │ │ │ │ │ │ +┌────────────────────────────────────────────────▼───┼───┼───┼───┼───┤ +│ UserRequestHandler [Fast Path Actor] │ │ │ │ │ +│ 🟦 CLASS (sealed) │ │ │ │ │ +│ │ │ │ │ │ +│ HandleRequestAsync(range, ct): │ │ │ │ │ +│ 1. _intentManager.CancelPendingRebalance() ──────┼───┼───┼───┼───┤ +│ 2. Check if cache covers range ──────────────────┼───┤ │ │ │ +│ 3. If not: _cacheFetcher.ExtendCacheAsync() ─────┼───┼───┤ │ │ +│ 4. If not: _state.Cache.Rematerialize() ─────────┼───┤ │ │ │ +│ 5. _state.LastRequested = range ─────────────────┼───┤ │ │ │ +│ 6. _intentManager.PublishIntent(range) ───────────┼───┼───┼───┼───┤ +│ 7. return _state.Cache.Read(range) ───────────────┼───┤ │ │ │ +└─────────────────────────────────────────────────────┼───┼───┼───┼───┘ + │ │ │ │ + ══════════════════════════════════════════════╪═══╪═══╪═══╪═══ + BACKGROUND / THREADPOOL │ │ │ │ + ══════════════════════════════════════════════╪═══╪═══╪═══╪═══ + │ │ │ │ +┌─────────────────────────────────────────────────────▼───┼───┼───┼───┐ +│ RebalanceIntentManager [Intent Controller] │ │ │ │ +│ 🟦 CLASS (sealed) │ │ │ │ +│ │ │ │ │ +│ Fields: │ │ │ │ +│ ├─ RebalanceScheduler _scheduler ─────────────────────▼───┼───┤ │ +│ └─ CancellationTokenSource? _currentIntentCts ◄───────────┤ │ │ +│ │ │ │ +│ PublishIntent(range): │ │ │ +│ 1. Cancel & dispose old _currentIntentCts │ │ │ +│ 2. Create new CancellationTokenSource │ │ │ +│ 3. _scheduler.ScheduleRebalance(range, token) ─────────────┼───┤ │ +│ │ │ │ +│ CancelPendingRebalance(): │ │ │ +│ 1. Cancel & dispose _currentIntentCts │ │ │ +└──────────────────────────────────────────────────────────────┼───┼───┘ + │ │ +┌──────────────────────────────────────────────────────────────▼───┼───┐ +│ RebalanceScheduler [Execution Scheduler] │ │ +│ 🟦 CLASS (sealed) │ │ +│ │ │ +│ ScheduleRebalance(range, intentToken): │ │ +│ Task.Run(async () => { │ │ +│ await Task.Delay(_debounceDelay, intentToken); │ │ +│ if (!intentToken.IsCancellationRequested) │ │ +│ await ExecutePipelineAsync(range, intentToken); ───────────┼───┤ +│ }); │ │ +│ │ │ +│ ExecutePipelineAsync(range, ct): │ │ +│ 1. Check cancellation │ │ +│ 2. decision = _decisionEngine.ShouldExecuteRebalance() ────────┼───┤ +│ 3. if (decision.ShouldExecute) │ │ +│ await _executor.ExecuteAsync(desiredRange, ct); ──────────┼───┤ +└───────────────────────────────────────────────────────────────────┼───┘ + │ +┌───────────────────────────────────────────────────────────────────▼──┐ +│ RebalanceDecisionEngine [Pure Decision Logic] │ +│ 🟦 CLASS (sealed) │ +│ │ +│ Fields (value types): │ +│ ├─ 🟩 ThresholdRebalancePolicy _policy │ +│ └─ 🟩 ProportionalRangePlanner _planner │ +│ │ +│ ShouldExecuteRebalance(requested, noRebalanceRange): │ +│ 1. Check if _policy.ShouldRebalance() → may skip │ +│ 2. desiredRange = _planner.Plan(requested) │ +│ 3. return Execute(desiredRange) or Skip() │ +│ │ +│ Returns: 🟩 RebalanceDecision │ +└────────────────────────────────────────────────────────────────────────┘ + +┌────────────────────────────────────────────────────────────────────────┐ +│ RebalanceExecutor [Mutating Actor] │ +│ 🟦 CLASS (sealed) │ +│ │ +│ ExecuteAsync(desiredRange, ct): │ +│ 1. rangeData = _state.Cache.ToRangeData() ──────────┐ │ +│ 2. if (rangeData.Range == desiredRange) return │ │ +│ 3. ct.ThrowIfCancellationRequested() │ │ +│ 4. extended = await _cacheFetcher.ExtendCacheAsync() ┼───────────┐ │ +│ 5. ct.ThrowIfCancellationRequested() │ │ │ +│ 6. rebalanced = extended[desiredRange] (trim) │ │ │ +│ 7. ct.ThrowIfCancellationRequested() │ │ │ +│ 8. _state.Cache.Rematerialize(rebalanced) ───────────┼───────┐ │ │ +│ 9. _state.NoRebalanceRange = ... ────────────────────┼───────┤ │ │ +└────────────────────────────────────────────────────────┼───────┼───┼──┘ + │ │ │ +┌────────────────────────────────────────────────────────▼───────┼───┼──┐ +│ CacheState [Shared Mutable State] │ │ │ +│ 🟦 CLASS (sealed) ⚠️ SHARED │ │ │ +│ │ │ │ +│ Properties: │ │ │ +│ ├─ ICacheStorage Cache ◄──────────────────────────────────────┼───┤ │ +│ ├─ Range? LastRequested ◄─ UserRequestHandler │ │ │ +│ ├─ Range? NoRebalanceRange ◄─ RebalanceExecutor │ │ │ +│ └─ TDomain Domain (readonly) │ │ │ +│ │ │ │ +│ Shared by: │ │ │ +│ ├─ UserRequestHandler (R/W) │ │ │ +│ ├─ RebalanceExecutor (R/W) │ │ │ +│ └─ RebalanceScheduler → DecisionEngine (R) │ │ │ +└─────────────────────────────────────────────────────────────────┼───┼──┘ + │ │ +┌─────────────────────────────────────────────────────────────────▼───┼──┐ +│ ICacheStorage │ │ +│ 🟧 INTERFACE │ │ +│ │ │ +│ Implementations: │ │ +│ ├─ 🟦 SnapshotReadStorage (TData[] array) │ │ +│ │ • Read: zero allocation (memory view) │ │ +│ │ • Write: expensive (allocates new array) │ │ +│ │ │ │ +│ └─ 🟦 CopyOnReadStorage (List) │ │ +│ • Read: allocates (copies to new array) │ │ +│ • Write: cheap (list operations) │ │ +│ │ │ +│ Methods: │ │ +│ ├─ void Rematerialize(RangeData) ⊲ WRITE │ │ +│ ├─ ReadOnlyMemory Read(Range) ⊳ READ │ │ +│ └─ RangeData ToRangeData() ⊳ READ │ │ +└──────────────────────────────────────────────────────────────────────┼──┘ + │ +┌──────────────────────────────────────────────────────────────────────▼──┐ +│ CacheDataExtensionService [Data Fetcher] │ +│ 🟦 CLASS (sealed) │ +│ │ +│ ExtendCacheAsync(current, requested, ct): │ +│ 1. missingRanges = CalculateMissingRanges() │ +│ 2. fetched = await _dataSource.FetchAsync(missingRanges, ct) ◄────┐ │ +│ 3. return UnionAll(current, fetched) (merge, no trim) │ │ +│ │ │ +│ Shared by: │ │ +│ ├─ UserRequestHandler (expand to requested) │ │ +│ └─ RebalanceExecutor (expand to desired) │ │ +└───────────────────────────────────────────────────────────────────────┼──┘ + │ +┌───────────────────────────────────────────────────────────────────────▼──┐ +│ IDataSource [External Data Source] │ +│ 🟧 INTERFACE (user-implemented) │ +│ │ +│ Methods: │ +│ ├─ FetchAsync(Range, CT) → Task> │ +│ └─ FetchAsync(IEnumerable, CT) → Task> │ +│ │ +│ Characteristics: │ +│ ├─ User-provided implementation │ +│ ├─ May perform I/O (network, disk, database) │ +│ ├─ Read-only (fetches data) │ +│ └─ Should respect CancellationToken │ +└───────────────────────────────────────────────────────────────────────────┘ +``` + +--- + +## Read/Write Patterns + +### CacheState (⚠️ Shared Mutable State) + +#### Writers + +**UserRequestHandler**: +- ✏️ Writes `LastRequested` property +- ✏️ Writes `Cache` (via `Rematerialize()`) + - **Purpose**: Expand cache to cover requested range + - **When**: User request needs data not in cache + - **Scope**: Expands only (never trims) + +**RebalanceExecutor**: +- ✏️ Writes `Cache` (via `Rematerialize()`) + - **Purpose**: Normalize cache to DesiredCacheRange + - **When**: Rebalance execution completes + - **Scope**: Expands AND trims +- ✏️ Writes `NoRebalanceRange` property + - **Purpose**: Update threshold zone after normalization + - **When**: After successful rebalance + +#### Readers + +**UserRequestHandler**: +- 👁️ Reads `Cache.Range` - Check if cache covers requested range +- 👁️ Reads `Cache.Read(range)` - Return data to user +- 👁️ Reads `Cache.ToRangeData()` - Get snapshot before extending + +**RebalanceScheduler** (via DecisionEngine): +- 👁️ Reads `NoRebalanceRange` - Decision logic (check if rebalance needed) + +**RebalanceExecutor**: +- 👁️ Reads `Cache.Range` - Check if already at desired range +- 👁️ Reads `Cache.ToRangeData()` - Get snapshot before normalizing + +#### Coordination + +**No locks** (by design): +- Single consumer model (one logical user per cache) +- Coordination via **CancellationToken** +- User Path **always cancels** rebalance before mutations +- Rebalance **always checks** cancellation before mutations + +**Atomic operations**: +- `Rematerialize()` replaces storage atomically (array/list assignment) +- Property writes are atomic (reference assignment) + +--- + +### CancellationTokenSource (Intent Identity) + +#### Owner: IntentController + +**Creates**: +- In `PublishIntent()` - new CTS for each intent + +**Cancels**: +- In `PublishIntent()` - cancels previous CTS (supersede old intent) +- In `CancelPendingRebalance()` - cancels current CTS (user priority) + +**Disposes**: +- Immediately after cancellation (prevent resource leaks) +- Sets to null after disposal (clean state) + +#### Users + +**RebalanceScheduler**: +- 👁️ Receives token from IntentManager +- 👁️ Checks `IsCancellationRequested` after debounce delay +- 👁️ Passes token to `ExecutePipelineAsync()` +- 👁️ Passes token to `Task.Delay()` (cancellable debounce) + +**RebalanceExecutor**: +- 👁️ Receives token from Scheduler +- 👁️ Calls `ThrowIfCancellationRequested()` at three points: + 1. After range equality check, before I/O + 2. After `ExtendCacheAsync()`, before trim + 3. Before `Rematerialize()` (prevent applying obsolete results) + +**CacheDataExtensionService**: +- 👁️ Receives token from caller (UserRequestHandler or RebalanceExecutor) +- 👁️ Passes token to `IDataSource.FetchAsync()` (cancellable I/O) + +--- + +## Thread Safety Model + +### Concurrency Philosophy + +The Sliding Window Cache follows a **single consumer model** as documented in `docs/concurrency-model.md`: + +> "A cache instance is **not thread-safe**, is **not designed for concurrent access**, and assumes a single, coherent access pattern. This is an **ideological requirement**, not merely an architectural or technical limitation." + +### Key Principles + +1. **Single Logical Consumer** + - One cache instance = one user + - One access trajectory + - One temporal sequence of requests + +2. **No Synchronization Primitives** + - ❌ No locks (`lock`, `Monitor`) + - ❌ No semaphores (`SemaphoreSlim`) + - ❌ No concurrent collections + - ✅ Only `CancellationToken` for coordination + +3. **Coordination Mechanism** + - User Path cancels rebalance **before** any cache mutation + - Rebalance checks cancellation **before and during** execution + - Atomic array/list replacement in `Rematerialize()` + +### Thread Contexts + +| Component | Thread Context | Notes | +|-----------------------------------|-------------------|----------------------------------------| +| **WindowCache** | Neutral | Just delegates | +| **UserRequestHandler** | ⚡ **User Thread** | Synchronous, fast path | +| **RebalanceIntentManager** | User Thread | Synchronous methods (called from user) | +| **RebalanceScheduler** | 🔄 **Background** | ThreadPool, async | +| **RebalanceDecisionEngine** | 🔄 **Background** | ThreadPool, pure logic | +| **RebalanceExecutor** | 🔄 **Background** | ThreadPool, async, I/O | +| **CacheDataExtensionService** | Both ⚡🔄 | User Thread OR Background | +| **CacheState** | Both ⚡🔄 | Shared mutable (no locks!) | +| **Storage (Snapshot/CopyOnRead)** | Both ⚡🔄 | Owned by CacheState | + +### Concurrency Invariants (from `docs/invariants.md`) + +**A.1 Concurrency & Priority**: +- **-1**: User Path **MUST NOT execute concurrently** with Rebalance Execution +- **0**: User Path **always has higher priority** than Rebalance Execution +- **0a**: Every User Request **MUST cancel** any ongoing/pending Rebalance before mutations + +**C. Rebalance Intent & Temporal Invariants**: +- **17**: At most **one active rebalance intent** +- **18**: Previous intents are **obsolete** after new intent +- **21**: At most **one rebalance execution** active at any time + +### How It Works + +#### User Request Flow (User Thread) +``` +1. UserRequestHandler.HandleRequestAsync() called +2. FIRST STEP: _intentManager.CancelPendingRebalance() + └─> Cancels CancellationTokenSource + └─> Background rebalance receives cancellation signal +3. Check cache, extend if needed +4. Mutate cache (Rematerialize) - safe, rebalance is cancelled +5. Publish new intent +6. Return data +``` + +#### Rebalance Flow (Background Thread) +``` +1. RebalanceScheduler.ScheduleRebalance() in Task.Run() +2. await Task.Delay() - cancellable debounce +3. Check IsCancellationRequested - early exit if cancelled +4. DecisionEngine.ShouldExecuteRebalance() - pure logic +5. RebalanceExecutor.ExecuteAsync() + ├─ ThrowIfCancellationRequested() before I/O + ├─ await _dataSource.FetchAsync() - cancellable I/O + ├─ ThrowIfCancellationRequested() after I/O + ├─ Trim data + ├─ ThrowIfCancellationRequested() before mutation + └─ Rematerialize() - atomic cache update +``` + +### Multi-User Scenarios + +**✅ Correct Approach**: +```csharp +// Create one cache instance per user +var userCache1 = new WindowCache(...); +var userCache2 = new WindowCache(...); +``` + +**❌ Incorrect Approach**: +```csharp +// DO NOT share cache across threads/users +var sharedCache = new WindowCache(...); +// Thread 1: sharedCache.GetDataAsync() - UNSAFE +// Thread 2: sharedCache.GetDataAsync() - UNSAFE +``` + +### Safety Guarantees + +**Provided**: +- ✅ User Path never waits for rebalance +- ✅ User Path always has priority (cancels rebalance) +- ✅ At most one rebalance execution active +- ✅ Obsolete rebalance results are discarded +- ✅ Cache state remains consistent (atomic Rematerialize) + +**Not Provided**: +- ❌ Thread-safe concurrent access (by design) +- ❌ Multiple consumers per cache (model violation) +- ❌ Cross-user sliding window arbitration (nonsensical) + +--- + +## Type Summary Tables + +### Reference Types (Classes) + +| Component | Mutability | Shared State | Ownership | Lifetime | +|---------------------------|----------------------------------------------|--------------|--------------------------|----------------| +| WindowCache | Immutable (after ctor) | No | User creates | App lifetime | +| UserRequestHandler | Immutable | No | WindowCache owns | Cache lifetime | +| CacheState | **Mutable** | **Yes** ⚠️ | WindowCache owns, shared | Cache lifetime | +| IntentController | Mutable (_currentIntentCts) | No | WindowCache owns | Cache lifetime | +| RebalanceScheduler | Immutable | No | IntentController owns | Cache lifetime | +| RebalanceDecisionEngine | Immutable | No | WindowCache owns | Cache lifetime | +| RebalanceExecutor | Immutable | No | WindowCache owns | Cache lifetime | +| CacheDataExtensionService | Immutable | No | WindowCache owns | Cache lifetime | +| SnapshotReadStorage | **Mutable** (_storage array) | No | CacheState owns | Cache lifetime | +| CopyOnReadStorage | **Mutable** (_activeStorage, _stagingBuffer) | No | CacheState owns | Cache lifetime | + +### Value Types (Structs) + +| Component | Mutability | Ownership | Lifetime | +|--------------------------|------------|------------------------|--------------------| +| ThresholdRebalancePolicy | Readonly | Copied into components | Component lifetime | +| ProportionalRangePlanner | Readonly | Copied into components | Component lifetime | +| RebalanceDecision | Readonly | Local variable | Method scope | + +### Other Types + +| Component | Type | Purpose | Mutability | +|--------------------|--------------|------------------------|------------| +| WindowCacheOptions | 🟨 Record | Configuration | Immutable | +| RangeChunk | 🟨 Record | Data transfer | Immutable | +| UserCacheReadMode | 🟪 Enum | Configuration option | Immutable | +| ICacheStorage | 🟧 Interface | Storage abstraction | - | +| IDataSource | 🟧 Interface | External data contract | - | + +--- + +## Component Responsibilities Summary + +### By Execution Context + +**User Thread (Synchronous, Fast)**: +- WindowCache - Facade, delegates +- UserRequestHandler - Serve requests, trigger intents + +**Background / ThreadPool (Asynchronous, Heavy)**: +- RebalanceScheduler - Timing, debounce, orchestration +- RebalanceDecisionEngine - Pure decision logic +- RebalanceExecutor - Cache normalization, I/O + +**Both Contexts**: +- CacheDataExtensionService - Data fetching (called by both paths) +- CacheState - Shared mutable state (accessed by both) + +### By Responsibility + +**Data Serving**: +- WindowCache (facade) +- UserRequestHandler (implementation) +- CacheState (storage) +- ICacheStorage implementations (actual data) + +**Intent Management**: +- IntentController (lifecycle) +- RebalanceScheduler (execution) + +**Decision Making**: +- RebalanceDecisionEngine (orchestrator) +- ThresholdRebalancePolicy (thresholds) +- ProportionalRangePlanner (geometry) + +**Mutation**: +- UserRequestHandler (expand only) +- RebalanceExecutor (normalize: expand + trim) + +**Data Fetching**: +- CacheDataExtensionService (internal) +- IDataSource (external, user-provided) + +--- + +## Architectural Patterns Used + +### 1. Facade Pattern +**WindowCache** acts as a facade that hides internal complexity and provides a simple public API. + +### 2. Composition Root +**WindowCache** constructor wires all components together in one place. + +### 3. Actor Model (Conceptual) +Components follow actor-like patterns with clear responsibilities and message passing (method calls). + +### 4. Intent Controller Pattern +**IntentController** manages versioned, cancellable operations through CancellationTokenSource identity. + +### 5. Strategy Pattern +**ICacheStorage** with two implementations (SnapshotReadStorage, CopyOnReadStorage) allows runtime selection of storage strategy. + +### 6. Value Object Pattern +**ThresholdRebalancePolicy**, **ProportionalRangePlanner**, **RebalanceDecision** are immutable value types with pure behavior. + +### 7. Shared Mutable State (Controlled) +**CacheState** is intentionally shared mutable state, coordinated via CancellationToken (not locks). + +### 8. Single Consumer Model +Entire architecture assumes one logical consumer, avoiding traditional concurrency primitives. + +--- + +## Related Documentation + +- **Architecture Overview**: `docs/actors-to-components-mapping.md` +- **Responsibilities**: `docs/actors-and-responsibilities.md` +- **Invariants**: `docs/invariants.md` +- **Scenarios**: `docs/scenario-model.md` +- **State Machine**: `docs/cache-state-machine.md` +- **Concurrency Model**: `docs/concurrency-model.md` +- **Storage Strategies**: `docs/storage-strategies.md` +- **Cache Hit/Miss Tracking**: `docs/cache-hit-miss-tracking-implementation.md` + +--- + +## Conclusion + +The Sliding Window Cache is composed of **19 components** working together to provide fast, cache-aware data access with automatic rebalancing: + +- **10 classes** (reference types) provide the runtime behavior +- **3 structs** (value types) provide pure, stateless logic +- **2 interfaces** define contracts for extensibility +- **2 records** provide immutable configuration and data transfer +- **1 enum** defines storage strategy options + +The architecture follows a **single consumer model** with **no traditional synchronization primitives**, relying instead on **CancellationToken** for coordination between the fast User Path and the async Rebalance Path. + +All components are designed with **clear ownership**, **explicit read/write patterns**, and **well-defined responsibilities**, making the system predictable, testable, and maintainable. diff --git a/docs/concurrency-model.md b/docs/concurrency-model.md new file mode 100644 index 0000000..7b6ae69 --- /dev/null +++ b/docs/concurrency-model.md @@ -0,0 +1,256 @@ +# Concurrency Model + +## Core Principle + +This library is built around a **single logical consumer per cache instance** with a **single-writer architecture**. + +A cache instance: +- is **not thread-safe for shared access** +- is **designed for concurrent reads** (User Path is read-only) +- assumes a single, coherent access pattern +- enforces single-writer for all mutations (Rebalance Execution only) + +This is an **ideological requirement**, not merely an architectural or technical limitation. + +The architecture of the library reflects and enforces this principle. + +--- + +## Single-Writer Architecture + +### Core Design + +The cache implements a **single-writer** concurrency model: + +- **One Writer:** Rebalance Execution Path exclusively +- **Read-Only User Path:** User Path never mutates cache state +- **No Locks:** Coordination via cancellation, not mutual exclusion +- **Eventual Consistency:** Cache state converges asynchronously to optimal configuration + +### Write Ownership + +Only `RebalanceExecutor` may write to: +- Cache data and range (via `Cache.Rematerialize()`) +- `LastRequested` field +- `NoRebalanceRange` field + +All other components have read-only access to cache state. + +### Read Safety + +User Path safely reads cache state without locks because: +- User Path never writes to cache (read-only guarantee) +- Rebalance Execution performs atomic updates via `Rematerialize()` +- Cancellation ensures Rebalance Execution yields before User Path operations +- Single-writer eliminates race conditions + +### Eventual Consistency Model + +Cache state converges to optimal configuration asynchronously: + +1. **User Path** returns correct data immediately (from cache or IDataSource) +2. **User Path** publishes intent with delivered data +3. **Cache state** updates occur in background via Rebalance Execution +4. **Debounce delay** controls convergence timing +5. **User correctness** never depends on cache state being up-to-date + +**Key insight:** User always receives correct data, regardless of whether cache has converged yet. + +--- + +## Single Cache Instance = Single Consumer + +A sliding window cache models the behavior of **one observer moving through data**. + +Each cache instance represents: +- one user +- one access trajectory +- one temporal sequence of requests + +Attempting to share a single cache instance across multiple users or threads +violates this fundamental assumption. + +**Note:** The single-consumer constraint exists for coherent access patterns, +not for mutation safety (User Path is read-only, so parallel reads would be safe +from a mutation perspective, but would still violate the single-consumer model). + +--- + +## Why This Is a Requirement (Not a Limitation) + +### 1. Sliding Window Requires a Unified Access Pattern + +The cache continuously adapts its window based on observed access. + +If multiple consumers request unrelated ranges: +- there is no single `DesiredCacheRange` +- the window oscillates or becomes unstable +- cache efficiency collapses + +This is not a concurrency bug — it is a **model mismatch**. + +--- + +### 2. Rebalance Logic Depends on a Single Timeline + +Rebalance behavior relies on: +- ordered intents +- cancellation of obsolete work +- "latest access wins" semantics +- eventual stabilization + +These guarantees require a **single temporal sequence of access events**. + +Multiple consumers introduce conflicting timelines that cannot be meaningfully +merged without fundamentally changing the model. + +--- + +### 3. Architecture Reflects the Ideology + +The system architecture: +- enforces single-thread access +- isolates rebalance logic from user code +- assumes coherent access intent + +These choices do not define the constraint — +they **exist to preserve it**. + +--- + +## How to Use This Library in Multi-User Environments + +### ✅ Correct Approach + +If your system has multiple users or concurrent consumers: + +> **Create one cache instance per user (or per logical consumer).** + +Each cache instance: +- operates independently +- maintains its own sliding window +- runs its own rebalance lifecycle + +This preserves correctness, performance, and predictability. + +--- + +### ❌ Incorrect Approach + +Do **not**: +- share a cache instance across threads +- multiplex multiple users through a single cache +- attempt to synchronize access externally + +External synchronization does not solve the underlying model conflict and will +result in inefficient or unstable behavior. + +--- + +## Deterministic Background Job Synchronization + +### Testing Infrastructure API + +The cache provides a `WaitForIdleAsync()` method for deterministic synchronization with +background rebalance operations. This is **infrastructure/testing API**, not part of normal +usage patterns or domain semantics. + +### Implementation + +**Mechanism**: Task lifecycle tracking via observe-and-stabilize pattern + +- `RebalanceScheduler` maintains `_idleTask` field tracking latest background Task +- `WaitForIdleAsync()` implements: + ``` + 1. Volatile.Read(_idleTask) → observe current Task + 2. await observedTask → wait for completion + 3. Re-check if _idleTask changed → detect new rebalance + 4. Loop until Task reference stabilizes + ``` +- Guarantees: No rebalance execution running when method returns +- Safety: Handles concurrent intent cancellation and rescheduling correctly +- Use cases: Testing, graceful shutdown, health checks, integration scenarios + +### Use Cases + +- **Test stabilization**: Ensure cache has converged before assertions +- **Integration testing**: Synchronize with background work completion +- **Diagnostic scenarios**: Verify rebalance execution finished + +### Architectural Preservation + +This synchronization mechanism does **not** alter actor responsibilities: + +- UserRequestHandler remains sole intent publisher +- IntentController remains lifecycle authority +- RebalanceScheduler remains execution authority +- WindowCache remains pure facade + +Method exists only to expose idle synchronization through public API for testing purposes. + +### Lock-Free Implementation + +**IntentController** uses lock-free synchronization: +- **No locks, no `lock` statements, no mutexes** +- Uses `Interlocked.Exchange` for atomic field replacement +- `_currentIntentCts` field atomically swapped during intent operations +- Thread-safe without blocking - guaranteed progress +- Zero contention overhead + +**Race Condition Prevention:** +```csharp +// Atomic replacement ensures no race conditions +var oldCts = Interlocked.Exchange(ref _currentIntentCts, newCts); +``` + +**Testing Coverage:** +- Lock-free behavior validated by `ConcurrencyStabilityTests` +- Tested under concurrent load (100+ simultaneous operations) +- No deadlocks, no race conditions, no data corruption observed + +This lightweight synchronization primitive ensures thread-safety without the overhead +and complexity of traditional locking mechanisms. + +### Relation to Concurrency Model + +The observe-and-stabilize pattern: +- Does not introduce locking or mutual exclusion +- Leverages existing single-writer architecture +- Provides visibility through volatile reads +- Maintains eventual consistency model + +This is synchronization **with** background work, not synchronization **of** concurrent writers. + +--- + +## What Is Supported + +- Single logical consumer per cache instance (coherent access pattern) +- Single-writer architecture (Rebalance Execution only) +- Read-only User Path (safe for repeated calls from same consumer) +- Background asynchronous rebalance +- Cancellation and debouncing of rebalance execution +- High-frequency access from one logical consumer +- Eventual consistency model (cache converges asynchronously) +- Intent-based data delivery (delivered data in intent avoids duplicate fetches) + +--- + +## What Is Explicitly Not Supported + +- Multiple concurrent consumers per cache instance +- Thread-safe shared access +- Cross-user sliding window arbitration + +--- + +## Design Philosophy + +This library prioritizes: +- conceptual clarity +- predictable behavior +- cache efficiency +- correctness of temporal and spatial logic + +Instead of providing superficial thread safety, +it enforces a model that remains stable, explainable, and performant. diff --git a/docs/diagnostics.md b/docs/diagnostics.md new file mode 100644 index 0000000..0a04b3b --- /dev/null +++ b/docs/diagnostics.md @@ -0,0 +1,696 @@ +# Cache Diagnostics - Instrumentation and Observability + +## Overview + +The Sliding Window Cache provides optional diagnostics instrumentation for monitoring cache behavior, measuring performance, validating system invariants, and understanding operational characteristics. The diagnostics system is designed as a **zero-cost abstraction** - when not used, it adds absolutely no runtime overhead. + +--- + +## Purpose and Use Cases + +### Primary Use Cases + +1. **Testing and Validation** + - Verify cache behavior matches expected patterns + - Validate system invariants during test execution + - Assert specific cache scenarios (hit/miss patterns, rebalance lifecycle) + - Enable deterministic testing with observable state + +2. **Performance Monitoring** + - Track cache hit/miss ratios in production or staging + - Measure rebalance frequency and patterns + - Identify access pattern inefficiencies + - Quantify data source interaction costs + +3. **Debugging and Development** + - Understand cache lifecycle events during development + - Trace User Path vs. Rebalance Execution behavior + - Identify unexpected cancellation patterns + - Verify optimization effectiveness (skip conditions) + +4. **Production Observability** (Optional) + - Export metrics to monitoring systems + - Track cache efficiency over time + - Correlate cache behavior with application performance + - Identify degradation patterns + +--- + +## Architecture + +### Interface: `ICacheDiagnostics` + +The diagnostics system is built around the `ICacheDiagnostics` interface, which defines 15 event recording methods corresponding to key cache behavioral events: + +```csharp +public interface ICacheDiagnostics +{ + // User Path Events + void UserRequestServed(); + void CacheExpanded(); + void CacheReplaced(); + void UserRequestFullCacheHit(); + void UserRequestPartialCacheHit(); + void UserRequestFullCacheMiss(); + + // Data Source Access Events + void DataSourceFetchSingleRange(); + void DataSourceFetchMissingSegments(); + + // Rebalance Intent Lifecycle Events + void RebalanceIntentPublished(); + void RebalanceIntentCancelled(); + + // Rebalance Execution Lifecycle Events + void RebalanceExecutionStarted(); + void RebalanceExecutionCompleted(); + void RebalanceExecutionCancelled(); + + // Rebalance Skip Optimization Events + void RebalanceSkippedNoRebalanceRange(); + void RebalanceSkippedSameRange(); +} +``` + +### Implementations + +#### `EventCounterCacheDiagnostics` - Default Implementation + +Thread-safe counter-based implementation that tracks all events using `Interlocked.Increment` for atomicity: + +```csharp +var diagnostics = new EventCounterCacheDiagnostics(); + +// Pass to cache constructor +var cache = new WindowCache( + dataSource: myDataSource, + domain: new IntegerFixedStepDomain(), + options: options, + cacheDiagnostics: diagnostics +); + +// Read counters +Console.WriteLine($"Cache hits: {diagnostics.UserRequestFullCacheHit}"); +Console.WriteLine($"Rebalances: {diagnostics.RebalanceExecutionCompleted}"); +``` + +**Features:** +- ✅ Thread-safe (uses `Interlocked.Increment`) +- ✅ Low overhead (integer increment per event) +- ✅ Read-only properties for all 16 counters (15 counters + 1 exception event) +- ✅ `Reset()` method for test isolation +- ✅ Instance-based (multiple caches can have separate diagnostics) +- ⚠️ **Warning**: Default implementation only writes RebalanceExecutionFailed to Debug output + +**Use for:** +- Testing and validation +- Development and debugging +- Production monitoring (acceptable overhead) + +**⚠️ CRITICAL: Production Usage Requirement** + +The default `EventCounterCacheDiagnostics` implementation of `RebalanceExecutionFailed` only writes to Debug output. **For production use, you MUST create a custom implementation that logs to your logging infrastructure.** + +```csharp +public class ProductionCacheDiagnostics : ICacheDiagnostics +{ + private readonly ILogger _logger; + private int _userRequestServed; + // ...other counters... + + public ProductionCacheDiagnostics(ILogger logger) + { + _logger = logger; + } + + public void RebalanceExecutionFailed(Exception ex) + { + // CRITICAL: Always log rebalance failures with full context + _logger.LogError(ex, + "Cache rebalance execution failed. Cache may not be optimally sized. " + + "Subsequent user requests will still be served but rebalancing has stopped."); + } + + // ...implement other diagnostic methods... +} +``` + +**Why this is critical:** + +Rebalance operations run in fire-and-forget background tasks. When exceptions occur: +1. The exception is caught and recorded via `RebalanceExecutionFailed` +2. The exception is swallowed to prevent application crashes +3. Without logging, failures are **completely silent** + +Ignoring this event means: +- ❌ Data source errors go unnoticed +- ❌ Cache stops rebalancing with no indication +- ❌ Performance degrades silently +- ❌ No diagnostics for troubleshooting + +**Recommended production implementation:** +- Always log with full exception details (message, stack trace, inner exceptions) +- Include structured context (cache instance ID, requested range if available) +- Consider alerting for repeated failures (circuit breaker pattern) +- Track failure rate metrics for monitoring dashboards + +#### `NoOpDiagnostics` - Zero-Cost Implementation + +Empty implementation with no-op methods that the JIT can optimize away completely: + +```csharp +// Automatically used when cacheDiagnostics parameter is omitted +var cache = new WindowCache( + dataSource: myDataSource, + domain: new IntegerFixedStepDomain(), + options: options + // cacheDiagnostics: null (default) -> uses NoOpDiagnostics +); +``` + +**Features:** +- ✅ **Absolute zero overhead** - methods are empty and get inlined/eliminated +- ✅ No memory allocations +- ✅ No performance impact whatsoever +- ✅ Default when diagnostics not provided + +**Use for:** +- Production deployments where diagnostics are not needed +- Performance-critical scenarios +- When observability is handled externally + +--- + +## Diagnostic Events Reference + +### User Path Events + +#### `UserRequestServed()` +**Tracks:** Completion of user request (data returned and intent published) +**Location:** `UserRequestHandler.HandleRequestAsync` (final step) +**Scenarios:** All user scenarios (U1-U5): cold start, full hit, partial hit, full miss/jump +**Interpretation:** Total number of user requests successfully served + +**Example Usage:** +```csharp +await cache.GetDataAsync(Range.Closed(100, 200), ct); +Assert.Equal(1, diagnostics.UserRequestServed); +``` + +--- + +#### `CacheExpanded()` +**Tracks:** Cache expansion during partial cache hit +**Location:** `CacheDataExtensionService.CalculateMissingRanges` (intersection path) +**Scenarios:** User Scenario U4 (partial cache hit) +**Invariant:** Invariant 9a (Cache Contiguity Rule - preserves contiguity) +**Interpretation:** Number of times cache grew while maintaining contiguity + +**Example Usage:** +```csharp +// Initial request: [100, 200] +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// Overlapping request: [150, 250] - triggers expansion +await cache.GetDataAsync(Range.Closed(150, 250), ct); + +Assert.Equal(1, diagnostics.CacheExpanded); +``` + +--- + +#### `CacheReplaced()` +**Tracks:** Cache replacement during non-intersecting jump +**Location:** `CacheDataExtensionService.CalculateMissingRanges` (no intersection path) +**Scenarios:** User Scenario U5 (full cache miss - jump) +**Invariant:** Invariant 9a (Cache Contiguity Rule - prevents gaps) +**Interpretation:** Number of times cache was fully replaced to maintain contiguity + +**Example Usage:** +```csharp +// Initial request: [100, 200] +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// Non-intersecting request: [500, 600] - triggers replacement +await cache.GetDataAsync(Range.Closed(500, 600), ct); + +Assert.Equal(1, diagnostics.CacheReplaced); +``` + +--- + +#### `UserRequestFullCacheHit()` +**Tracks:** Request served entirely from cache (no data source access) +**Location:** `UserRequestHandler.HandleRequestAsync` (Scenario 2) +**Scenarios:** User Scenarios U2, U3 (full cache hit) +**Interpretation:** Optimal performance - requested range fully contained in cache + +**Example Usage:** +```csharp +// Request 1: [100, 200] - cache miss, cache becomes [100, 200] +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// Request 2: [120, 180] - fully within [100, 200] +await cache.GetDataAsync(Range.Closed(120, 180), ct); + +Assert.Equal(1, diagnostics.UserRequestFullCacheHit); +``` + +--- + +#### `UserRequestPartialCacheHit()` +**Tracks:** Request with partial cache overlap (fetch missing segments) +**Location:** `UserRequestHandler.HandleRequestAsync` (Scenario 3) +**Scenarios:** User Scenario U4 (partial cache hit) +**Interpretation:** Efficient cache extension - some data reused, missing parts fetched + +**Example Usage:** +```csharp +// Request 1: [100, 200] +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// Request 2: [150, 250] - overlaps with [100, 200] +await cache.GetDataAsync(Range.Closed(150, 250), ct); + +Assert.Equal(1, diagnostics.UserRequestPartialCacheHit); +``` + +--- + +#### `UserRequestFullCacheMiss()` +**Tracks:** Request requiring complete fetch from data source +**Location:** `UserRequestHandler.HandleRequestAsync` (Scenarios 1 and 4) +**Scenarios:** U1 (cold start), U5 (non-intersecting jump) +**Interpretation:** Most expensive path - no cache reuse + +**Example Usage:** +```csharp +// Cold start - no cache +await cache.GetDataAsync(Range.Closed(100, 200), ct); +Assert.Equal(1, diagnostics.UserRequestFullCacheMiss); + +// Jump to non-intersecting range +await cache.GetDataAsync(Range.Closed(500, 600), ct); +Assert.Equal(2, diagnostics.UserRequestFullCacheMiss); +``` + +--- + +### Data Source Access Events + +#### `DataSourceFetchSingleRange()` +**Tracks:** Single contiguous range fetch from `IDataSource` +**Location:** `UserRequestHandler.HandleRequestAsync` (cold start or jump) +**API Called:** `IDataSource.FetchAsync(Range, CancellationToken)` +**Interpretation:** Complete range fetched as single operation + +**Example Usage:** +```csharp +// Cold start or jump - fetches entire range as one operation +await cache.GetDataAsync(Range.Closed(100, 200), ct); +Assert.Equal(1, diagnostics.DataSourceFetchSingleRange); +``` + +--- + +#### `DataSourceFetchMissingSegments()` +**Tracks:** Missing segments fetch (gap filling optimization) +**Location:** `CacheDataExtensionService.ExtendCacheAsync` +**API Called:** `IDataSource.FetchAsync(IEnumerable>, CancellationToken)` +**Interpretation:** Optimized fetch of only missing data segments + +**Example Usage:** +```csharp +// Request 1: [100, 200] +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// Request 2: [150, 250] - fetches only [201, 250] +await cache.GetDataAsync(Range.Closed(150, 250), ct); + +Assert.Equal(1, diagnostics.DataSourceFetchMissingSegments); +``` + +--- + +### Rebalance Intent Lifecycle Events + +#### `RebalanceIntentPublished()` +**Tracks:** Rebalance intent publication by User Path +**Location:** `IntentController.PublishIntent` (after scheduler receives intent) +**Invariants:** A.3 (User Path is sole source of intent), 24e (Intent contains delivered data) +**Note:** Intent publication does NOT guarantee execution (opportunistic) + +**Example Usage:** +```csharp +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// Every user request publishes exactly one intent +Assert.Equal(1, diagnostics.RebalanceIntentPublished); +``` + +--- + +#### `RebalanceIntentCancelled()` +**Tracks:** Intent cancellation before or during execution +**Location:** `RebalanceScheduler` (three cancellation points) +**Invariants:** A.0 (User Path priority), A.0a (User cancels rebalance), C.20 (Obsolete intent doesn't start) +**Interpretation:** Single-flight execution - new request cancels previous intent + +**Example Usage:** +```csharp +var options = new WindowCacheOptions(debounceDelay: TimeSpan.FromSeconds(1)); +var cache = TestHelpers.CreateCache(domain, diagnostics, options); + +// Request 1 - publishes intent, starts debounce delay +var task1 = cache.GetDataAsync(Range.Closed(100, 200), ct); + +// Request 2 (before debounce completes) - cancels previous intent +var task2 = cache.GetDataAsync(Range.Closed(300, 400), ct); + +await Task.WhenAll(task1, task2); +await cache.WaitForIdleAsync(); + +Assert.True(diagnostics.RebalanceIntentCancelled >= 1); +``` + +--- + +### Rebalance Execution Lifecycle Events + +#### `RebalanceExecutionStarted()` +**Tracks:** Rebalance execution start after decision approval +**Location:** `RebalanceScheduler.ExecutePipelineAsync` (after DecisionEngine approval) +**Scenarios:** Decision Scenario D3 (rebalance required) +**Invariant:** 28 (Rebalance triggered only if confirmed necessary) + +**Example Usage:** +```csharp +await cache.GetDataAsync(Range.Closed(100, 200), ct); +await cache.WaitForIdleAsync(); + +Assert.Equal(1, diagnostics.RebalanceExecutionStarted); +``` + +--- + +#### `RebalanceExecutionCompleted()` +**Tracks:** Successful rebalance completion +**Location:** `RebalanceExecutor.ExecuteAsync` (after UpdateCacheState) +**Scenarios:** Rebalance Scenarios R1, R2 (build from scratch, expand cache) +**Invariants:** 34 (Only Rebalance writes to cache), 35 (Atomic state update) + +**Example Usage:** +```csharp +await cache.GetDataAsync(Range.Closed(100, 200), ct); +await cache.WaitForIdleAsync(); + +Assert.Equal(1, diagnostics.RebalanceExecutionCompleted); +``` + +--- + +#### `RebalanceExecutionCancelled()` +**Tracks:** Rebalance cancellation mid-flight +**Location:** `RebalanceScheduler.ExecutePipelineAsync` (catch OperationCanceledException) +**Invariant:** 34a (Rebalance yields to User Path immediately) +**Interpretation:** User Path priority enforcement - rebalance interrupted + +**Example Usage:** +```csharp +// Long-running rebalance scenario +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// New request while rebalance is executing +await cache.GetDataAsync(Range.Closed(300, 400), ct); +await cache.WaitForIdleAsync(); + +// First rebalance was cancelled +Assert.True(diagnostics.RebalanceExecutionCancelled >= 1); +``` + +--- + +#### `RebalanceExecutionFailed(Exception ex)` ⚠️ CRITICAL +**Tracks:** Rebalance execution failure due to exception +**Location:** `RebalanceScheduler.ExecutePipelineAsync` (catch Exception after executor call) +**Interpretation:** **CRITICAL ERROR** - background rebalance operation failed + +**⚠️ WARNING: This event MUST be handled in production applications** + +Rebalance operations execute in fire-and-forget background tasks. When an exception occurs: +1. The exception is caught and this event is recorded +2. The exception is silently swallowed to prevent application crashes +3. The cache continues serving user requests but rebalancing stops + +**Consequences of ignoring this event:** +- ❌ Silent failures in background operations +- ❌ Cache stops rebalancing without any indication +- ❌ Performance degrades with no diagnostics +- ❌ Data source errors go completely unnoticed +- ❌ Impossible to troubleshoot production issues + +**Minimum requirement: Always log** + +```csharp +public void RebalanceExecutionFailed(Exception ex) +{ + _logger.LogError(ex, + "Cache rebalance execution failed. Cache will continue serving user requests " + + "but rebalancing has stopped. Investigate data source health and cache configuration."); +} +``` + +**Recommended production implementation:** + +```csharp +public class RobustCacheDiagnostics : ICacheDiagnostics +{ + private readonly ILogger _logger; + private readonly IMetrics _metrics; + private int _consecutiveFailures; + + public void RebalanceExecutionFailed(Exception ex) + { + // 1. Always log with full context + _logger.LogError(ex, + "Cache rebalance execution failed. ConsecutiveFailures: {Failures}", + Interlocked.Increment(ref _consecutiveFailures)); + + // 2. Track metrics for monitoring + _metrics.Counter("cache.rebalance.failures", 1); + + // 3. Alert on repeated failures (circuit breaker) + if (_consecutiveFailures >= 5) + { + _logger.LogCritical( + "Cache rebalancing has failed {Failures} times consecutively. " + + "Consider investigating data source health or disabling cache.", + _consecutiveFailures); + } + } + + public void RebalanceExecutionCompleted() + { + // Reset failure counter on success + Interlocked.Exchange(ref _consecutiveFailures, 0); + } + + // ...other methods... +} +``` + +**Common failure scenarios:** +- Data source timeouts or connectivity issues +- Data source throws exceptions for specific ranges +- Memory pressure during large cache expansions +- Serialization/deserialization failures +- Configuration errors (invalid ranges, domain issues) + +**Example Usage (Testing):** +```csharp +// Simulate data source failure +var faultyDataSource = new FaultyDataSource(); +var cache = new WindowCache( + dataSource: faultyDataSource, + domain: new IntegerFixedStepDomain(), + options: options, + cacheDiagnostics: diagnostics +); + +await cache.GetDataAsync(Range.Closed(100, 200), ct); +await cache.WaitForIdleAsync(); + +// Verify failure was recorded +Assert.Equal(1, diagnostics.RebalanceExecutionFailed); +``` + +--- + +### Rebalance Skip Optimization Events + +#### `RebalanceSkippedNoRebalanceRange()` +**Tracks:** Rebalance skipped due to NoRebalanceRange policy +**Location:** `RebalanceScheduler.ExecutePipelineAsync` (DecisionEngine returns ShouldExecute=false) +**Scenarios:** Decision Scenario D1 (inside no-rebalance threshold) +**Invariants:** D.26 (No rebalance if inside NoRebalanceRange), D.27 (Policy-based skip) + +**Example Usage:** +```csharp +var options = new WindowCacheOptions( + leftThreshold: 0.3, + rightThreshold: 0.3 +); + +// Request 1 establishes cache and NoRebalanceRange +await cache.GetDataAsync(Range.Closed(100, 200), ct); +await cache.WaitForIdleAsync(); + +// Request 2 inside NoRebalanceRange - skips rebalance +await cache.GetDataAsync(Range.Closed(120, 180), ct); +await cache.WaitForIdleAsync(); + +Assert.True(diagnostics.RebalanceSkippedNoRebalanceRange >= 1); +``` + +--- + +#### `RebalanceSkippedSameRange()` +**Tracks:** Rebalance skipped because ranges already match +**Location:** `RebalanceExecutor.ExecuteAsync` (before expensive I/O) +**Scenarios:** Decision Scenario D2 (DesiredCacheRange == CurrentCacheRange) +**Invariants:** D.27 (No rebalance if same range), D.28 (Same-range optimization) + +**Example Usage:** +```csharp +// Delivered data range already matches desired range +await cache.GetDataAsync(Range.Closed(100, 200), ct); +await cache.WaitForIdleAsync(); + +// Rebalance started but detected same-range condition +Assert.True(diagnostics.RebalanceSkippedSameRange >= 0); // May or may not occur +``` + +--- + +## Testing Patterns + +### Test Isolation with Reset() + +```csharp +[Fact] +public async Task Test_CacheHitPattern() +{ + var diagnostics = new EventCounterCacheDiagnostics(); + var cache = CreateCache(diagnostics); + + // Setup + await cache.GetDataAsync(Range.Closed(100, 200), ct); + await cache.WaitForIdleAsync(); + + // Reset to isolate test scenario + diagnostics.Reset(); + + // Test + await cache.GetDataAsync(Range.Closed(120, 180), ct); + + // Assert only test scenario events + Assert.Equal(1, diagnostics.UserRequestFullCacheHit); + Assert.Equal(0, diagnostics.UserRequestPartialCacheHit); + Assert.Equal(0, diagnostics.UserRequestFullCacheMiss); +} +``` + +--- + +### Invariant Validation + +```csharp +public static void AssertRebalanceLifecycleIntegrity(EventCounterCacheDiagnostics d) +{ + // Published >= Started (some intents may be cancelled before execution) + Assert.True(d.RebalanceIntentPublished >= d.RebalanceExecutionStarted); + + // Started == Completed + Cancelled (every started execution completes or is cancelled) + Assert.Equal(d.RebalanceExecutionStarted, + d.RebalanceExecutionCompleted + d.RebalanceExecutionCancelled); +} +``` + +--- + +### User Path Scenario Verification + +```csharp +public static void AssertPartialCacheHit(EventCounterCacheDiagnostics d, int expectedCount = 1) +{ + Assert.Equal(expectedCount, d.UserRequestPartialCacheHit); + Assert.Equal(expectedCount, d.CacheExpanded); + Assert.Equal(expectedCount, d.DataSourceFetchMissingSegments); +} +``` + +--- + +## Performance Considerations + +### Runtime Overhead + +**`EventCounterCacheDiagnostics` (when enabled):** +- ~1-5 nanoseconds per event (single `Interlocked.Increment`) +- Negligible compared to cache operations (microseconds to milliseconds) +- Thread-safe with no locks +- No allocations + +**`NoOpDiagnostics` (default):** +- **Absolute zero overhead** - methods are inlined and eliminated by JIT +- No memory footprint +- No performance impact + +### Memory Overhead + +- `EventCounterCacheDiagnostics`: 60 bytes (15 integers) +- `NoOpDiagnostics`: 0 bytes (no state) + +### Recommendation + +- **Development/Testing**: Always use `EventCounterCacheDiagnostics` +- **Production**: Use `EventCounterCacheDiagnostics` if monitoring is needed, omit otherwise +- **Performance-critical paths**: Omit diagnostics entirely (uses `NoOpDiagnostics`) + +--- + +## Custom Implementations + +You can implement `ICacheDiagnostics` for custom observability scenarios: + +```csharp +public class PrometheusMetricsDiagnostics : ICacheDiagnostics +{ + private readonly Counter _requestsServed; + private readonly Counter _cacheHits; + private readonly Counter _cacheMisses; + + public PrometheusMetricsDiagnostics(IMetricFactory metricFactory) + { + _requestsServed = metricFactory.CreateCounter("cache_requests_total"); + _cacheHits = metricFactory.CreateCounter("cache_hits_total"); + _cacheMisses = metricFactory.CreateCounter("cache_misses_total"); + } + + public void UserRequestServed() => _requestsServed.Inc(); + public void UserRequestFullCacheHit() => _cacheHits.Inc(); + public void UserRequestPartialCacheHit() => _cacheHits.Inc(); + public void UserRequestFullCacheMiss() => _cacheMisses.Inc(); + + // ... implement other methods +} +``` + +--- + +## See Also + +- **[Invariants](invariants.md)** - System invariants tracked by diagnostics +- **[Scenario Model](scenario-model.md)** - User/Decision/Rebalance scenarios referenced in event descriptions +- **[Invariant Test Suite](../tests/SlidingWindowCache.Invariants.Tests/README.md)** - Examples of diagnostic usage in tests +- **[Component Map](component-map.md)** - Component locations where events are recorded diff --git a/docs/invariants.md b/docs/invariants.md new file mode 100644 index 0000000..fe55230 --- /dev/null +++ b/docs/invariants.md @@ -0,0 +1,441 @@ +# Sliding Window Cache — System Invariants (Classified) + +--- + +## Understanding This Document + +This document lists **46 system invariants** that define the behavior, architecture, and design intent of the Sliding Window Cache. + +### Invariant Categories + +Invariants are classified into three categories based on their **nature** and **enforcement mechanism**: + +#### 🟢 Behavioral Invariants +- **Nature**: Externally observable behavior via public API +- **Enforcement**: Automated tests (unit, integration) +- **Verification**: Can be tested through public API without inspecting internal state +- **Examples**: User request behavior, returned data correctness, cancellation effects + +#### 🔵 Architectural Invariants +- **Nature**: Internal structural constraints enforced by code organization +- **Enforcement**: Component boundaries, encapsulation, ownership model +- **Verification**: Code review, type system, access modifiers +- **Examples**: Atomicity of state updates, component responsibilities, separation of concerns +- **Note**: NOT directly testable via public API (would require white-box testing or test hooks) + +#### 🟡 Conceptual Invariants +- **Nature**: Design intent, guarantees, or explicit non-guarantees +- **Enforcement**: Documentation and architectural discipline +- **Verification**: Design reviews, documentation +- **Examples**: "Intent does not guarantee execution", opportunistic behavior, allowed inefficiencies +- **Note**: Guide future development; NOT meant to be tested directly + +### Important Meta-Point: Invariants ≠ Test Coverage + +**By design, this document contains MORE invariants than the test suite covers.** + +This is intentional and correct: +- ✅ **Behavioral invariants** → Covered by automated tests +- ✅ **Architectural invariants** → Enforced by code structure, not tests +- ✅ **Conceptual invariants** → Documented design decisions, not test cases + +**Full invariant documentation does NOT imply full test coverage.** +Different invariant types are enforced at different levels: +- Tests verify externally observable behavior +- Architecture enforces internal structure +- Documentation guides design decisions + +Attempting to test architectural or conceptual invariants would require: +- Invasive test hooks or reflection (anti-pattern) +- White-box testing of implementation details (brittle) +- Testing things that are enforced by the type system or compiler + +**This separation is a feature, not a gap.** + +--- + +## Testing Infrastructure: Deterministic Synchronization + +### Background + +Tests verify behavioral invariants through the public API using instrumentation counters +(DEBUG-only) to observe internal state changes. However, tests also need to **synchronize** with background +rebalance operations to ensure cache has converged before making assertions. + +### Synchronization Mechanism: `WaitForIdleAsync()` + +The cache exposes a public `WaitForIdleAsync()` method for deterministic synchronization with +background rebalance execution: + +- **Purpose**: Infrastructure/testing API (not part of domain semantics) +- **Mechanism**: Task lifecycle tracking using observe-and-stabilize pattern +- **Guarantee**: Returns only when no rebalance execution is running +- **Safety**: Works correctly under concurrent intent cancellation and rescheduling + +### Implementation Strategy + +- `RebalanceScheduler` tracks latest background Task in `_idleTask` field +- `WaitForIdleAsync()` implements observe-and-stabilize loop: + 1. Read current `_idleTask` via `Volatile.Read` (ensures visibility) + 2. Await the observed Task + 3. Re-check if `_idleTask` changed (new rebalance scheduled) + 4. Loop until Task reference stabilizes and completes + +This provides deterministic synchronization useful for testing, graceful shutdown, +health checks, and other infrastructure scenarios. + +### Architectural Boundaries + +This synchronization mechanism **does not alter actor responsibilities**: + +- ✅ UserRequestHandler remains the ONLY publisher of rebalance intents +- ✅ IntentController remains the lifecycle authority for intent cancellation +- ✅ RebalanceScheduler remains the authority for background Task execution +- ✅ WindowCache remains a composition root with no business logic + +The method exists solely to expose idle synchronization through the public API for testing, +maintaining architectural separation. + +### Relation to Instrumentation Counters + +Instrumentation counters track **events** (intent published, execution started, etc.) but are +not used for synchronization. The observe-and-stabilize pattern based on Task lifecycle provides +deterministic, race-free synchronization without polling or timing dependencies. + +**Old approach (removed):** +- Counter-based polling with stability windows +- Timing-dependent with configurable intervals +- Complex lifecycle calculation + +**Current approach:** +- Direct Task lifecycle tracking +- Deterministic (no timing assumptions) +- Simple and race-free + +--- + +## A. User Path & Fast User Access Invariants + +### A.1 Concurrency & Priority + +**A.-1** 🔵 **[Architectural]** The User Path and Rebalance Execution **never write to cache concurrently**. +- *Enforced by*: Single-writer architecture - User Path is read-only, only Rebalance Execution writes +- *Architecture*: User Path never mutates cache state; Rebalance Execution is sole writer + +**A.0** 🔵 **[Architectural]** The User Path **always has higher priority** than Rebalance Execution. +- *Enforced by*: Component ownership, cancellation protocol +- *Architecture*: User Path cancels rebalance; rebalance checks cancellation + +**A.0a** 🟢 **[Behavioral — Test: `Invariant_A_0a_UserRequestCancelsRebalance`]** Every User Request **MUST cancel** any ongoing or pending Rebalance Execution to ensure rebalance doesn't interfere with User Path data assembly. +- *Observable via*: DEBUG instrumentation counters tracking cancellation +- *Test verifies*: Cancellation counter increments when new request arrives +- *Note*: Cancellation ensures User Path priority, not mutation safety (User Path is read-only) + +### A.2 User-Facing Guarantees + +**A.1** 🟢 **[Behavioral — Test: `Invariant_A2_1_UserPathAlwaysServesRequests`]** The User Path **always serves user requests** regardless of the state of rebalance execution. +- *Observable via*: Public API always returns data successfully +- *Test verifies*: Multiple requests all complete and return correct data + +**A.2** 🟢 **[Behavioral — Test: `Invariant_A2_2_UserPathNeverWaitsForRebalance`]** The User Path **never waits for rebalance execution** to complete. +- *Observable via*: Request completion time vs. debounce delay +- *Test verifies*: Request completes in <500ms with 1-second debounce + +**A.3** 🔵 **[Architectural]** The User Path is the **sole source of rebalance intent**. +- *Enforced by*: Only `UserRequestHandler` calls `IntentController.PublishIntent()` +- *Architecture*: Encapsulation prevents other components from publishing intents + +**A.4** 🔵 **[Architectural]** Rebalance execution is **always performed asynchronously** relative to the User Path. +- *Enforced by*: `Task.Run()` in `RebalanceScheduler`, fire-and-forget pattern +- *Architecture*: User Path returns immediately after publishing intent + +**A.5** 🔵 **[Architectural]** The User Path performs **only the work necessary to return data to the user**. +- *Enforced by*: Responsibility assignment, component boundaries +- *Architecture*: `UserRequestHandler` doesn't normalize/trim cache + +**A.6** 🟡 **[Conceptual]** The User Path may synchronously request data from `IDataSource` in the user execution context if needed to serve `RequestedRange`. +- *Design decision*: Prioritizes user-facing latency over background work +- *Rationale*: User must get data immediately; background prefetch is opportunistic + +**A.10** 🟢 **[Behavioral — Test: `Invariant_A2_10_UserAlwaysReceivesExactRequestedRange`]** The User always receives data **exactly corresponding to `RequestedRange`**. +- *Observable via*: Returned data length and content +- *Test verifies*: Data matches requested range exactly (no more, no less) + +### A.3 Cache Mutation Rules (User Path) + +**A.7** 🔵 **[Architectural]** The User Path may read from cache and `IDataSource` but **does not mutate cache state**. +- *Enforced by*: Component responsibilities, read-only architecture +- *Architecture*: User Path has no write access to cache, LastRequested, or NoRebalanceRange + +**A.8** 🔵 **[Architectural — Tests: `Invariant_A3_8_ColdStart`, `_CacheExpansion`, `_FullCacheReplacement`]** The User Path **MUST NOT mutate cache under any circumstance**. + - User Path is **read-only** with respect to cache state + - User Path **NEVER** calls `Cache.Rematerialize()` + - User Path **NEVER** writes to `LastRequested` + - User Path **NEVER** writes to `NoRebalanceRange` + - All cache mutations are performed exclusively by Rebalance Execution (single-writer) +- *Observable via*: Instrumentation counters (`CacheExpanded`, `CacheReplaced`) track when CacheDataExtensionService analyzes extension needs +- *Test verifies*: User Path returns correct data without mutating cache; Rebalance Execution populates cache +- *Note*: `CacheExpanded/Replaced` counters are incremented by shared service (`CacheDataExtensionService`) used by both paths during range analysis, not mutation. Tests verify User Path doesn't trigger these counters in specific scenarios where prior rebalance has already expanded cache sufficiently. + +**A.9** 🔵 **[Architectural]** Cache mutations are performed **exclusively by Rebalance Execution** (single-writer architecture). +- *Enforced by*: Component encapsulation, internal setters on CacheState +- *Architecture*: Only `RebalanceExecutor` has write access to cache state + +**A.9a** 🟢 **[Behavioral — Test: `Invariant_A3_9a_CacheContiguityMaintained`]** **Cache Contiguity Rule:** `CacheData` **MUST always remain contiguous** — gapped or partially materialized cache states are invalid. +- *Observable via*: All requests return valid contiguous data +- *Test verifies*: Sequential overlapping requests all succeed + +--- + +## B. Cache State & Consistency Invariants + +**B.11** 🟢 **[Behavioral — Test: `Invariant_B11_CacheDataAndRangeAlwaysConsistent`]** `CacheData` and `CurrentCacheRange` are **always consistent** with each other. +- *Observable via*: Data length always matches range size +- *Test verifies*: For any request, returned data length matches expected range size + +**B.12** 🔵 **[Architectural]** Changes to `CacheData` and the corresponding `CurrentCacheRange` are performed **atomically**. +- *Enforced by*: `Rematerialize()` performs atomic swap (staging buffer pattern) +- *Architecture*: Tuple swap `(_activeStorage, _stagingBuffer) = (_stagingBuffer, _activeStorage)` is atomic + +**B.13** 🔵 **[Architectural]** The system **never enters a permanently inconsistent state** with respect to `CacheData ↔ CurrentCacheRange`. +- *Enforced by*: Atomic operations, cancellation checks before mutations +- *Architecture*: `ThrowIfCancellationRequested()` prevents applying obsolete results + +**B.14** 🟡 **[Conceptual]** Temporary geometric or coverage inefficiencies in the cache are acceptable **if they can be resolved by rebalance execution**. +- *Design decision*: User Path prioritizes speed over optimal cache shape +- *Rationale*: Background rebalance will normalize; temporary inefficiency is acceptable + +**B.15** 🟢 **[Behavioral — Test: `Invariant_B15_CancelledRebalanceDoesNotViolateConsistency`]** Partially executed or cancelled rebalance execution **cannot violate `CacheData ↔ CurrentCacheRange` consistency**. +- *Observable via*: Cache continues serving valid data after cancellation +- *Test verifies*: Rapid request changes don't corrupt cache + +**B.16** 🔵 **[Architectural]** Results from rebalance execution are applied **only if they correspond to the latest active rebalance intent**. +- *Enforced by*: Cancellation token identity, checks before `Rematerialize()` +- *Architecture*: `ThrowIfCancellationRequested()` before applying changes + +--- + +## C. Rebalance Intent & Temporal Invariants + +**C.17** 🟢 **[Behavioral — Test: `Invariant_C17_AtMostOneActiveIntent`]** At any point in time, there is **at most one active rebalance intent**. +- *Observable via*: DEBUG counters showing intent published/cancelled +- *Test verifies*: Multiple rapid requests show N published, N-1 cancelled + +**C.18** 🟢 **[Behavioral — Test: `Invariant_C18_PreviousIntentBecomesObsolete`]** Any previously created rebalance intent is **considered obsolete** after a new intent is generated. +- *Observable via*: DEBUG counters tracking intent lifecycle +- *Test verifies*: Old intent cancelled when new one published + +**C.19** 🔵 **[Architectural]** Any rebalance execution can be **cancelled or have its results ignored**. +- *Enforced by*: `CancellationToken` passed through execution pipeline +- *Architecture*: All async operations check cancellation token + +**C.20** 🔵 **[Architectural]** If a rebalance intent becomes obsolete before execution begins, the execution **must not start**. +- *Enforced by*: `IsCancellationRequested` check after debounce +- *Architecture*: Early exit in `RebalanceScheduler.ExecutePipelineAsync` + +**C.21** 🔵 **[Architectural]** At any point in time, **at most one rebalance execution is active**. +- *Enforced by*: Cancellation protocol, single intent identity +- *Architecture*: New intent cancels old execution via token + +**C.22** 🟡 **[Conceptual]** The results of rebalance execution **always reflect the latest user access pattern**. +- *Design guarantee*: Obsolete results are discarded +- *Rationale*: System converges to user's actual navigation pattern + +**C.23** 🟢 **[Behavioral — Test: `Invariant_C23_SystemStabilizesUnderLoad`]** During spikes of user requests, the system **eventually stabilizes** to a consistent cache state. +- *Observable via*: After burst of requests, system serves data correctly +- *Test verifies*: Rapid burst + wait → final request succeeds + +**C.24** 🟡 **[Conceptual — Test: `Invariant_C24_IntentDoesNotGuaranteeExecution`]** **Intent does not guarantee execution. Execution is opportunistic and may be skipped entirely.** + - Publishing an intent does NOT guarantee that rebalance will execute + - Execution may be cancelled before starting (due to new intent) + - Execution may be cancelled during execution (User Path priority) + - Execution may be skipped by DecisionEngine (NoRebalanceRange, DesiredRange == CurrentRange) + - This is by design: intent represents "user accessed this range", not "must rebalance" +- *Design decision*: Rebalance is opportunistic, not mandatory +- *Test note*: Test verifies skip behavior exists, but non-execution is acceptable + +**C.24e** 🔵 **[Architectural]** Intent **MUST contain delivered data** (`RangeData`) representing what was actually returned to the user for the requested range. +- *Enforced by*: `PublishIntent()` signature requires `deliveredData` parameter +- *Architecture*: User Path materializes data once and passes to both user and intent + +**C.24f** 🟡 **[Conceptual]** Delivered data in intent serves as the **authoritative source** for Rebalance Execution, avoiding duplicate fetches and ensuring consistency with user view. +- *Design guarantee*: Rebalance Execution uses delivered data as base, not current cache +- *Rationale*: Eliminates redundant IDataSource calls, ensures cache converges to what user received + +--- + +## D. Rebalance Decision Path Invariants + +**D.25** 🔵 **[Architectural]** The Rebalance Decision Path is **purely analytical** and has **no side effects**. +- *Enforced by*: `RebalanceDecisionEngine` is stateless, uses value types +- *Architecture*: Pure function: inputs → decision (no I/O, no mutations) + +**D.26** 🔵 **[Architectural]** The Decision Path **never mutates cache state**. +- *Enforced by*: No write access to `CacheState` in decision components +- *Architecture*: Decision components don't have reference to mutable cache + +**D.27** 🟢 **[Behavioral — Test: `Invariant_D27_NoRebalanceIfRequestInNoRebalanceRange`]** If `RequestedRange` is fully contained within `NoRebalanceRange`, **rebalance execution is prohibited**. +- *Observable via*: DEBUG counters showing execution skipped (policy-based, see C.24b) +- *Test verifies*: Request within NoRebalanceRange doesn't trigger execution + +**D.28** 🟢 **[Behavioral — Test: `Invariant_D28_SkipWhenDesiredEqualsCurrentRange`]** If `DesiredCacheRange == CurrentCacheRange`, **rebalance execution is not required**. +- *Observable via*: DEBUG counter `RebalanceSkippedSameRange` (optimization-based, see C.24c) +- *Test verifies*: Repeated request with same range increments skip counter +- *Implementation*: Early exit in `RebalanceExecutor.ExecuteAsync` before I/O operations + +**D.29** 🔵 **[Architectural]** Rebalance execution is triggered **only if the Decision Path confirms necessity**. +- *Enforced by*: `RebalanceScheduler` checks decision before calling executor +- *Architecture*: Decision result gates execution + +--- + +## E. Cache Geometry & Policy Invariants + +**E.30** 🟢 **[Behavioral — Test: `Invariant_E30_DesiredRangeComputedFromConfigAndRequest`]** `DesiredCacheRange` is computed **solely from `RequestedRange` and cache configuration**. +- *Observable via*: After rebalance, cache covers expected expanded range +- *Test verifies*: With config (leftSize=1.0, rightSize=1.0), cache expands as expected + +**E.31** 🔵 **[Architectural]** `DesiredCacheRange` is **independent of the current cache contents**, but may use configuration and `RequestedRange`. +- *Enforced by*: `ProportionalRangePlanner.Plan()` doesn't access current cache +- *Architecture*: Pure function using only config + requested range + +**E.32** 🟡 **[Conceptual]** `DesiredCacheRange` represents the **canonical target state** towards which the system converges. +- *Design concept*: Single source of truth for "what cache should be" +- *Rationale*: Ensures deterministic convergence behavior + +**E.33** 🟡 **[Conceptual]** The geometry of the sliding window is **determined by configuration**, not by scenario-specific logic. +- *Design principle*: Configuration drives behavior, not hard-coded heuristics +- *Rationale*: Predictable, user-controllable cache shape + +**E.34** 🔵 **[Architectural]** `NoRebalanceRange` is derived **from `CurrentCacheRange` and configuration**. +- *Enforced by*: `ThresholdRebalancePolicy.GetNoRebalanceRange()` implementation +- *Architecture*: Shrinks current range by threshold ratios + +--- + +## F. Rebalance Execution Invariants + +### F.1 Execution Control & Cancellation + +**F.35** 🟢 **[Behavioral — Test: `Invariant_F35_RebalanceExecutionSupportsCancellation`]** Rebalance Execution **MUST support cancellation** at all stages (before I/O, during I/O, before mutations). +- *Observable via*: DEBUG counters showing execution cancelled, lifecycle tracking (Started == Completed + Cancelled) +- *Test verifies*: Rapid requests cancel pending rebalance, execution lifecycle properly tracked +- *Implementation details*: `ThrowIfCancellationRequested()` at multiple checkpoints in execution pipeline +- *Related*: C.24d (execution skipped due to cancellation), A.0a (User Path triggers cancellation), G.46 (high-level guarantee) + +**F.35a** 🔵 **[Architectural]** Rebalance Execution **MUST yield** to User Path requests immediately upon cancellation. +- *Enforced by*: `ThrowIfCancellationRequested()` at multiple checkpoints +- *Architecture*: Cancellation checks before/after I/O, before mutations + +**F.35b** 🟢 **[Behavioral — Covered by `Invariant_B15`]** Partially executed or cancelled Rebalance Execution **MUST NOT leave cache in inconsistent state**. +- *Observable via*: Cache continues serving valid data after cancellation +- *Same test as B.15* + +### F.2 Cache Mutation Rules (Rebalance Execution) + +**F.36** 🔵 **[Architectural]** The Rebalance Execution Path is the **ONLY component that mutates cache state** (single-writer architecture). +- *Enforced by*: Component encapsulation, internal setters on CacheState +- *Architecture*: Only `RebalanceExecutor` writes to Cache, LastRequested, NoRebalanceRange + +**F.36a** 🟢 **[Behavioral — Test: `Invariant_F36a_RebalanceNormalizesCache`]** Rebalance Execution mutates cache for normalization using **delivered data from intent as authoritative base**: + - **Uses delivered data** from intent (not current cache) as starting point + - **Expanding to DesiredCacheRange** by fetching only truly missing ranges + - **Trimming excess data** outside `DesiredCacheRange` + - **Writing to cache** via `Cache.Rematerialize()` + - **Writing to LastRequested** with original requested range + - **Recomputing NoRebalanceRange** based on final cache range +- *Observable via*: After rebalance, cache serves data from expanded range +- *Test verifies*: Cache covers larger area after rebalance completes +- *Single-writer guarantee*: These are the ONLY mutations in the system + +**F.37** 🔵 **[Architectural]** Rebalance Execution may **replace, expand, or shrink cache data** to achieve normalization. +- *Enforced by*: `RebalanceExecutor` has full mutation capability +- *Architecture*: Can call `Rematerialize()` with any range + +**F.38** 🔵 **[Architectural]** Rebalance Execution requests data from `IDataSource` **only for missing subranges**. +- *Enforced by*: `CacheDataExtensionService.ExtendCacheAsync()` calculates missing ranges +- *Architecture*: Union logic preserves existing data + +**F.39** 🔵 **[Architectural]** Rebalance Execution **does not overwrite existing data** that intersects with `DesiredCacheRange`. +- *Enforced by*: `ExtendCacheAsync()` unions new data with existing +- *Architecture*: Staging buffer pattern preserves active storage during enumeration + +### F.3 Post-Execution Guarantees + +**F.40** 🟢 **[Behavioral — Test: `Invariant_F40_F41_F42_PostExecutionGuarantees`]** Upon successful completion, `CacheData` **strictly corresponds to `DesiredCacheRange`**. +- *Observable via*: After rebalance, cache serves data from expected normalized range +- *Test verifies*: Can read from expected expanded range + +**F.41** 🟢 **[Behavioral — Covered by same test as F.40]** Upon successful completion, `CurrentCacheRange == DesiredCacheRange`. +- *Observable indirectly*: Cache behavior matches expected range +- *Same test as F.40* + +**F.42** 🟡 **[Conceptual — Covered by same test as F.40]** Upon successful completion, `NoRebalanceRange` is **recomputed**. +- *Internal state*: Not directly observable via public API +- *Design guarantee*: Threshold zone updated after normalization + +--- + +## G. Execution Context & Scheduling Invariants + +**G.43** 🟢 **[Behavioral — Test: `Invariant_G43_G44_G45_ExecutionContextSeparation`]** The User Path operates in the **user execution context**. +- *Observable via*: Request completes quickly without waiting for background work +- *Test verifies*: Request time < debounce delay + +**G.44** 🔵 **[Architectural — Covered by same test as G.43]** Rebalance Decision Path and Rebalance Execution Path execute **outside the user execution context**. +- *Enforced by*: `Task.Run()` executes in ThreadPool +- *Architecture*: Fire-and-forget pattern, async execution + +**G.45** 🔵 **[Architectural — Covered by same test as G.43]** Rebalance Execution Path performs I/O **only in a background execution context**. +- *Enforced by*: `ExecuteAsync` runs in ThreadPool thread +- *Architecture*: User Path returns before background I/O starts + +**G.46** 🟢 **[Behavioral — Tests: `Invariant_G46_UserCancellationDuringFetch`, `Invariant_G46_RebalanceCancellation`]** Cancellation **must be supported** for all scenarios: +1. **User-facing cancellation**: User-provided CancellationToken propagates through User Path to IDataSource.FetchAsync() +2. **Background rebalance cancellation**: New user requests cancel pending/ongoing rebalance execution +- *Observable via*: + - User cancellation: OperationCanceledException thrown during IDataSource fetch + - Rebalance cancellation: DEBUG counters showing intent/execution cancelled +- *Test verifies*: + - `Invariant_G46_UserCancellationDuringFetch`: Cancelling during IDataSource fetch throws OperationCanceledException + - `Invariant_G46_RebalanceCancellation`: Background rebalance supports cancellation (high-level guarantee) +- *Related*: F.35 (detailed rebalance execution cancellation mechanics), A.0a (User Path priority via cancellation) + +--- + +## Summary Statistics + +### Total Invariants: 47 + +#### By Category: +- 🟢 **Behavioral** (test-covered): 19 invariants +- 🔵 **Architectural** (structure-enforced): 20 invariants +- 🟡 **Conceptual** (design-level): 8 invariants + +#### Test Coverage Analysis: +- **29 automated tests** in `WindowCacheInvariantTests` +- **19 behavioral invariants** directly covered +- **20 architectural invariants** enforced by code structure (not tested) +- **8 conceptual invariants** documented as design guidance (not tested) + +**This is by design.** The gap between 47 invariants and 29 tests is intentional: +- Architecture enforces structural constraints automatically +- Conceptual invariants guide development, not runtime behavior +- Tests focus on externally observable behavior + +### Cross-References + +For each behavioral invariant, the corresponding test is referenced in the invariant description. + +For architectural invariants, the enforcement mechanism (component, boundary, pattern) is documented. + +For conceptual invariants, the design rationale is explained. + +--- + +## Related Documentation + +- **[Component Map](component-map.md)** - Detailed component responsibilities and ownership +- **[Concurrency Model](concurrency-model.md)** - Single-consumer model and coordination +- **[Scenario Model](scenario-model.md)** - Temporal behavior scenarios +- **[Storage Strategies](storage-strategies.md)** - Staging buffer pattern and memory behavior diff --git a/docs/scenario-model.md b/docs/scenario-model.md new file mode 100644 index 0000000..bf6b147 --- /dev/null +++ b/docs/scenario-model.md @@ -0,0 +1,459 @@ +# Sliding Window Cache — Scenario Model (Temporal Perspective) + +This document describes the complete behavioral model of the Sliding Window Cache +from a temporal and procedural perspective. + +The goal is to explicitly capture all possible execution scenarios and paths +before projecting them onto architectural components, responsibilities, and APIs. + +The model is structured into three independent but sequentially connected paths +(one logically follows another): + +1. User Path — synchronous, user-facing behavior +2. Rebalance Decision Path — validation and decision making +3. Rebalance Execution Path — asynchronous cache normalization + +--- + +## Base Definitions + +The following terms are used consistently across all scenarios: + +- **RequestedRange** + A range requested by the user. + +- **LastRequestedRange** + The most recent range served by the User Path. + +- **CurrentCacheRange** + The range of data currently stored in the cache. + +- **CacheData** + The data corresponding to CurrentCacheRange. + +- **DesiredCacheRange** + The target cache range computed from RequestedRange and cache configuration + (left/right expansion sizes, thresholds, etc.). + +- **NoRebalanceRange** + A range inside which cache rebalance is not required. + +- **IDataSource** + A sequential, range-based data source. + +--- + +## Testing Infrastructure Note + +**Deterministic Synchronization**: Tests use `cache.WaitForIdleAsync()` to synchronize with +background rebalance completion. This is infrastructure/testing API implementing an +observe-and-stabilize pattern based on Task lifecycle tracking. + +This synchronization mechanism is **not part of the domain flow** described below. +It exists solely to enable deterministic testing without timing dependencies. + +See [Concurrency Model](concurrency-model.md) for implementation details. + +--- + +# I. USER PATH — User-Facing Scenarios + +*(Synchronous — executed in the user's thread)* + +The User Path is responsible only for: + +- deciding how to serve the user request +- selecting the data source (cache or IDataSource) +- triggering rebalance (without executing it) + +--- + +## User Scenario U1 — Cold Cache Request + +### Preconditions + +- `LastRequestedRange == null` +- `CurrentCacheRange == null` +- `CacheData == null` + +### Action Sequence + +1. User requests RequestedRange +2. Cache detects that it is not initialized +3. Cache requests RequestedRange from IDataSource in the user thread + (this is unavoidable because the user request must be served) +4. Received data: + - is stored as CacheData + - CurrentCacheRange is set to RequestedRange + - LastRequestedRange is set to RequestedRange +5. Rebalance is triggered asynchronously (fire-and-forget background work) +6. Data is immediately returned to the user + +**Note:** +The User Path does not expand the cache beyond RequestedRange. + +--- + +## User Scenario U2 — Full Cache Hit (Exact Match with LastRequestedRange) + +### Preconditions + +- Cache is initialized +- `RequestedRange == LastRequestedRange` +- `CurrentCacheRange.Contains(RequestedRange) == true` + +### Action Sequence + +1. User requests RequestedRange +2. Cache detects a full cache hit +3. Data is read from CacheData +4. LastRequestedRange is updated +5. Rebalance is triggered asynchronously + (because `NoRebalanceRange.Contains(RequestedRange)` may be false) +6. Data is returned to the user + +--- + +## User Scenario U3 — Full Cache Hit (Shifted Range) + +### Preconditions + +- Cache is initialized +- `RequestedRange != LastRequestedRange` +- `CurrentCacheRange.Contains(RequestedRange) == true` + +### Action Sequence + +1. User requests RequestedRange +2. Cache detects that all requested data is available +3. Subrange is read from CacheData +4. LastRequestedRange is updated +5. Rebalance is triggered asynchronously +6. Data is returned to the user + +--- + +## User Scenario U4 — Partial Cache Hit + +### Preconditions + +- Cache is initialized +- `CurrentCacheRange.Intersects(RequestedRange) == true` +- `CurrentCacheRange.Contains(RequestedRange) == false` + +### Action Sequence + +1. User requests RequestedRange +2. Cache computes intersection with CurrentCacheRange +3. Missing part is synchronously requested from IDataSource +4. Cache: + - merges cached and newly fetched data (cache expansion) + - does **not** trim excess data + - updates CurrentCacheRange to cover both old and new data +5. LastRequestedRange is updated +6. Rebalance is triggered asynchronously +7. RequestedRange data is returned to the user + +**Note:** +Cache expansion is permitted here because RequestedRange intersects CurrentCacheRange, +preserving cache contiguity. Excess data may temporarily remain in CacheData for reuse during Rebalance. + +--- + +## User Scenario U5 — Full Cache Miss (Jump) + +### Preconditions + +- Cache is initialized +- `CurrentCacheRange.Intersects(RequestedRange) == false` + +### Action Sequence + +1. User requests RequestedRange +2. Cache determines that RequestedRange does NOT intersect with CurrentCacheRange +3. **Cache contiguity enforcement:** Cached data cannot be preserved (would create gaps) +4. RequestedRange is synchronously requested from IDataSource +5. Cache: + - **fully replaces** CacheData with new data + - **fully replaces** CurrentCacheRange with RequestedRange +6. LastRequestedRange is updated +7. Rebalance is triggered asynchronously +8. Data is returned to the user + +**Critical Note:** +Partial cache expansion is FORBIDDEN in this case, as it would create logical gaps +and violate the Cache Contiguity Rule (Invariant 9a). The cache MUST remain contiguous. + +--- + +# II. REBALANCE DECISION PATH — Decision Scenarios + +**Important**: Intent does not guarantee execution. Execution is opportunistic. + +Publishing a rebalance intent does NOT mean rebalance will execute. The decision path +may determine that execution is not needed (NoRebalanceRange containment, or +DesiredRange == CurrentRange), in which case execution is skipped. Additionally, +intents may be superseded or cancelled before execution begins. + +The Rebalance Decision Path: + +- never mutates cache state +- may result in a no-op +- determines whether execution is required + +This path is always triggered by the User Path. + +--- + +## Decision Scenario D1 — Rebalance Blocked by NoRebalanceRange + +### Condition + +- `NoRebalanceRange.Contains(RequestedRange) == true` + +### Sequence + +1. Decision path starts +2. NoRebalanceRange is checked +3. Fast return — rebalance is skipped + (Execution Path is not started) + +--- + +## Decision Scenario D2 — Rebalance Allowed but Desired Equals Current + +### Condition + +- `NoRebalanceRange.Contains(RequestedRange) == false` +- `DesiredCacheRange == CurrentCacheRange` + +### Sequence + +1. Decision path starts +2. NoRebalanceRange is checked — no fast return +3. DesiredCacheRange is computed +4. Desired equals Current +5. Fast return — rebalance is skipped + (Execution Path is not started) + +--- + +## Decision Scenario D3 — Rebalance Required + +### Condition + +- `NoRebalanceRange.Contains(RequestedRange) == false` +- `DesiredCacheRange != CurrentCacheRange` + +### Sequence + +1. Decision path starts +2. NoRebalanceRange is checked — no fast return +3. DesiredCacheRange is computed +4. Desired differs from Current +5. Rebalance necessity is confirmed +6. Execution Path is started asynchronously + +--- + +# III. REBALANCE EXECUTION PATH — Execution Scenarios + +The Execution Path is the only path that: + +- performs I/O +- mutates cache state +- normalizes cache structure + +--- + +## Rebalance Scenario R1 — Build from Scratch + +### Preconditions + +- `CurrentCacheRange == null` + +**OR** + +- `DesiredCacheRange.Intersects(CurrentCacheRange) == false` + +### Sequence + +1. DesiredCacheRange is requested from IDataSource +2. CacheData is fully replaced +3. CurrentCacheRange is set to DesiredCacheRange +4. NoRebalanceRange is computed + +--- + +## Rebalance Scenario R2 — Expand Cache (Partial Overlap) + +### Preconditions + +- `DesiredCacheRange.Intersects(CurrentCacheRange) == true` +- `DesiredCacheRange != CurrentCacheRange` + +### Sequence + +1. Missing subranges are computed +2. Missing data is requested from IDataSource +3. Data is merged with existing CacheData +4. CacheData is normalized to DesiredCacheRange +5. NoRebalanceRange is updated + +--- + +## Rebalance Scenario R3 — Shrink / Normalize Cache + +### Preconditions + +- `CurrentCacheRange.Contains(DesiredCacheRange) == true` + +### Sequence + +1. CacheData is trimmed to DesiredCacheRange +2. CurrentCacheRange is updated +3. NoRebalanceRange is recomputed + +--- + +# IV. CONCURRENCY & CANCELLATION SCENARIOS + +This section describes temporal and concurrency-related scenarios +that occur when user requests arrive while rebalance logic is pending +or already executing. + +These scenarios are fundamental to the **Fast User Access** philosophy +and define how obsolete background work must be handled. + +--- + +## Concurrency Principles + +The Sliding Window Cache follows these rules: + +1. User Path is never blocked by rebalance logic +2. Multiple rebalance triggers may overlap in time +3. Only the **latest rebalance intent** is relevant +4. Obsolete rebalance work must be cancelled or abandoned +5. Rebalance execution must support cancellation +6. Cache state may be temporarily inconsistent but must be overwrite-safe + +--- + +## Concurrency Scenario C1 — Rebalance Triggered While Previous Rebalance Is Pending + +### Situation +- User request U₁ triggers rebalance R₁ (fire-and-forget) +- R₁ has not started execution yet (queued or delayed) +- User request U₂ arrives before R₁ executes + +### Expected Behavior +1. **U₂ cancels any pending rebalance work before performing its own cache mutations** +2. User Path for U₂ executes normally and immediately +3. A new rebalance trigger R₂ is issued +4. R₁ is cancelled or marked obsolete +5. Only R₂ is allowed to proceed to execution + +**Outcome:** +No rebalance work is executed based on outdated user intent. User Path always has priority. + +--- + +## Concurrency Scenario C2 — Rebalance Triggered While Previous Rebalance Is Executing + +### Situation +- User request U₁ triggers rebalance R₁ +- R₁ has already started execution (I/O or merge in progress) +- User request U₂ arrives and triggers rebalance R₂ + +### Expected Behavior +1. **U₂ cancels ongoing rebalance execution R₁ before performing its own cache mutations** +2. User Path for U₂ executes normally and immediately +3. R₂ becomes the latest rebalance intent +4. R₁ receives a cancellation signal +5. R₁: + - stops execution as early as possible, OR + - completes but discards its results +6. R₂ proceeds with fresh DesiredCacheRange + +**Outcome:** +Cache normalization reflects the most recent user access pattern. User Path and Rebalance Execution never mutate cache concurrently. + +--- + +## Concurrency Scenario C3 — Multiple Rapid User Requests (Spike / Random Access) + +### Situation +- User produces a burst of requests: U₁, U₂, U₃, ..., Uₙ +- Each request triggers rebalance +- Rebalance execution cannot keep up with trigger rate + +### Expected Behavior +1. User Path always serves requests independently +2. Rebalance triggers are debounced or superseded +3. At most one rebalance execution is active at any time +4. Only the final rebalance intent is executed +5. All intermediate rebalance work is cancelled or skipped + +**Outcome:** +System remains responsive and converges to a stable cache state +once user activity slows down. + +--- + +## Cancellation and State Safety Guarantees + +To support these scenarios, the following guarantees must hold: + +- Rebalance execution must be cancellable +- Cache mutations must be atomic or overwrite-safe +- Partial rebalance results must not corrupt cache state +- Final rebalance always produces a fully normalized cache + +Temporary inconsistency is acceptable. +Permanent inconsistency is not. + +--- + +## Design Note + +Concurrency handling is a **behavioral requirement**, not an implementation detail. + +The specific mechanism (cancellation tokens, versioning, actors, single-flight execution) +is intentionally left unspecified and will be defined during architectural projection. + +--- + +# Final Picture + +- User Path is fast, synchronous, and always responds +- Decision Path is lightweight and often results in no-op +- Execution Path is heavy, isolated, and asynchronous + +All scenarios: + +- are responsibility-isolated +- are expressed as temporal processes +- are independent of specific storage implementations + +--- + +## Notes and Considerations + +1. Decision Path and Execution Path should not execute in the user thread. + Even though the Decision Path is lightweight and often results in no-op, + it may still involve asynchronous I/O (IDataSource access). + + Using a ThreadPool-based or background scheduling approach aligns with + the core philosophy of SlidingWindowCache: + **fast user access with minimal mandatory work in the user thread**. + +2. Rebalance Execution scenarios (R1–R3) may be implemented as a unified pipeline: + - compute missing ranges + - request missing data + - merge with existing CacheData (if any) + - trim to DesiredCacheRange + - recompute NoRebalanceRange + + This document intentionally keeps these scenarios separate, as they describe + **semantic behavior**, not implementation strategy. diff --git a/docs/storage-strategies.md b/docs/storage-strategies.md new file mode 100644 index 0000000..affda53 --- /dev/null +++ b/docs/storage-strategies.md @@ -0,0 +1,443 @@ +# Sliding Window Cache - Storage Strategies Guide + +## Overview + +The WindowCache supports two distinct storage strategies, selectable via `WindowCacheOptions.ReadMode`: + +1. **Snapshot Storage** - Optimized for read performance +2. **CopyOnRead Storage with Staging Buffer** - Optimized for rematerialization performance + +This guide explains when to use each strategy and their trade-offs. + +--- + +## Storage Strategy Comparison + +| Aspect | Snapshot Storage | CopyOnRead Storage | +|------------------------|-----------------------------------|-----------------------------------| +| **Read Cost** | O(1) - zero allocation | O(n) - allocates and copies | +| **Rematerialize Cost** | O(n) - always allocates new array | O(1)* - reuses capacity | +| **Memory Pattern** | Single array, replaced atomically | Dual buffers, swapped atomically | +| **Buffer Growth** | Always allocates exact size | Grows but never shrinks | +| **LOH Risk** | High for >85KB arrays | Lower (List growth strategy) | +| **Best For** | Read-heavy workloads | Rematerialization-heavy workloads | +| **Typical Use Case** | User-facing cache layer | Background cache layer | + +*Amortized O(1) when capacity is sufficient + +--- + +## Snapshot Storage + +### Design + +``` +┌─────────────────────────────────┐ +│ SnapshotReadStorage │ +├─────────────────────────────────┤ +│ _storage: TData[] │ ← Single array +│ Range: Range │ +└─────────────────────────────────┘ +``` + +### Behavior + +**Rematerialize:** + +```csharp +_storage = rangeData.Data.ToArray(); // Always allocates new array +Range = rangeData.Range; +``` + +**Read:** + +```csharp +return new ReadOnlyMemory(_storage, offset, length); // Zero allocation +``` + +### Characteristics + +- ✅ **Zero-allocation reads**: Returns `ReadOnlyMemory` slice over internal array +- ✅ **Simple and predictable**: Single buffer, no complexity +- ❌ **Expensive rematerialization**: Always allocates new array (even if size unchanged) +- ❌ **LOH pressure**: Arrays ≥85KB go to Large Object Heap (no compaction) + +### When to Use + +- **Read-to-rematerialization ratio > 10:1** +- **Repeated reads of the same range** (user scrolling back/forth) +- **Small to medium cache sizes** (<85KB to avoid LOH) +- **User-facing cache layers** where read latency matters + +### Example Scenario + +```csharp +// User-facing viewport cache for UI data grid +var options = new WindowCacheOptions( + leftCacheSize: 0.5, + rightCacheSize: 0.5, + readMode: UserCacheReadMode.Snapshot // ← Zero-allocation reads +); + +var cache = new WindowCache( + dataSource, domain, options); + +// User scrolls: many reads, few rebalances +for (int i = 0; i < 100; i++) +{ + var data = await cache.GetDataAsync(Range.Closed(i, i + 20), ct); + // ← Zero allocation on each read +} +``` + +--- + +## CopyOnRead Storage with Staging Buffer + +### Design + +``` +┌─────────────────────────────────┐ +│ CopyOnReadStorage │ +├─────────────────────────────────┤ +│ _activeStorage: List │ ← Active (immutable during reads) +│ _stagingBuffer: List │ ← Staging (write-only during rematerialize) +│ Range: Range │ +└─────────────────────────────────┘ + +Rematerialize Flow: +┌──────────────┐ ┌──────────────┐ +│ Active │ │ Staging │ +│ [old data] │ │ [empty] │ +└──────────────┘ └──────────────┘ + ↓ Clear() preserves capacity + ┌──────────────┐ + │ Staging │ + │ [] │ + └──────────────┘ + ↓ AddRange(newData) + ┌──────────────┐ + │ Staging │ + │ [new data] │ + └──────────────┘ + ↓ Swap references +┌──────────────┐ ┌──────────────┐ +│ Active │ ←── │ Staging │ +│ [new data] │ │ [old data] │ +└──────────────┘ └──────────────┘ +``` + +### Staging Buffer Pattern + +The dual-buffer pattern solves a critical correctness issue: + +**Problem:** When `rangeData.Data` is derived from the same storage (e.g., LINQ chain during cache expansion), mutating +storage during enumeration corrupts the data. + +**Solution:** Never mutate active storage during enumeration. Instead: + +1. Materialize into separate staging buffer +2. Atomically swap buffer references +3. Reuse old active buffer as staging for next operation + +### Behavior + +**Rematerialize:** + +```csharp +_stagingBuffer.Clear(); // Preserves capacity +_stagingBuffer.AddRange(rangeData.Data); // Single-pass enumeration +(_activeStorage, _stagingBuffer) = (_stagingBuffer, _activeStorage); // Atomic swap +Range = rangeData.Range; +``` + +**Read:** + +```csharp +var result = new TData[length]; // Allocates +_activeStorage.CopyTo(offset, result, 0, length); +return new ReadOnlyMemory(result); +``` + +### Characteristics + +- ✅ **Cheap rematerialization**: Reuses capacity, no allocation if size ≤ capacity +- ✅ **No LOH pressure**: List growth strategy avoids large single allocations +- ✅ **Correct enumeration**: Staging buffer prevents corruption +- ✅ **Amortized performance**: Cost decreases over time as capacity stabilizes +- ❌ **Expensive reads**: Each read allocates and copies +- ❌ **Higher memory**: Two buffers instead of one + +### Memory Behavior + +- **Buffers may grow but never shrink**: Amortizes allocation cost +- **Capacity reuse**: Once buffers reach steady state, no more allocations during rematerialization +- **Predictable**: No hidden allocations, clear worst-case behavior + +### When to Use + +- **Rematerialization-to-read ratio > 1:5** (frequent rebalancing) +- **Large sliding windows** (>100KB typical size) +- **Random access patterns** (frequent non-intersecting jumps) +- **Background cache layers** feeding other caches +- **Composition scenarios** (described below) + +### Example Scenario: Multi-Level Cache Composition + +```csharp +// BACKGROUND LAYER: Large distant cache with CopyOnRead +var backgroundOptions = new WindowCacheOptions( + leftCacheSize: 10.0, // Cache 10x requested range + rightCacheSize: 10.0, + leftThreshold: 0.3, + rightThreshold: 0.3, + readMode: UserCacheReadMode.CopyOnRead // ← Cheap rematerialization +); + +var backgroundCache = new WindowCache( + slowDataSource, // Network/disk + domain, + backgroundOptions +); + +// USER-FACING LAYER: Small nearby cache with Snapshot +var userOptions = new WindowCacheOptions( + leftCacheSize: 0.5, + rightCacheSize: 0.5, + readMode: UserCacheReadMode.Snapshot // ← Zero-allocation reads +); + +// Wrap background cache as IDataSource for user cache +IDataSource cachedDataSource = new CacheDataSourceAdapter(backgroundCache); + +var userCache = new WindowCache( + cachedDataSource, // Reads from background cache + domain, + userOptions +); + +// User scrolls: +// - userCache: many reads (zero-alloc), rare rebalancing +// - backgroundCache: infrequent reads (copy), frequent rebalancing +``` + +This composition leverages the strengths of both strategies: + +- **Background layer**: Handles large distant window, absorbs rebalancing cost +- **User layer**: Handles small nearby window, serves reads with zero allocation + +--- + +## Decision Matrix + +### Choose **Snapshot** if: + +1. ✅ You expect **many reads per rematerialization** (>10:1 ratio) +2. ✅ Cache size is **predictable and modest** (<85KB) +3. ✅ Read latency is **critical** (user-facing UI) +4. ✅ Memory allocation during rematerialization is **acceptable** + +### Choose **CopyOnRead** if: + +1. ✅ You expect **frequent rematerialization** (random access, non-sequential) +2. ✅ Cache size is **large** (>100KB) +3. ✅ Read latency is **less critical** (background layer) +4. ✅ You want to **amortize allocation cost** over time +5. ✅ You're building a **multi-level cache composition** + +### Default Recommendation + +- **User-facing caches**: Start with **Snapshot** +- **Background caches**: Start with **CopyOnRead** +- **Unsure**: Start with **Snapshot**, profile, switch if rebalancing becomes bottleneck + +--- + +## Performance Characteristics + +### Snapshot Storage + +| Operation | Time | Allocation | +|---------------|------|---------------| +| Read | O(1) | 0 bytes | +| Rematerialize | O(n) | n × sizeof(T) | +| ToRangeData | O(1) | 0 bytes* | + +*Returns lazy enumerable + +### CopyOnRead Storage + +| Operation | Time | Allocation | +|----------------------|------|---------------| +| Read | O(n) | n × sizeof(T) | +| Rematerialize (cold) | O(n) | n × sizeof(T) | +| Rematerialize (warm) | O(n) | 0 bytes** | +| ToRangeData | O(1) | 0 bytes* | + +*Returns lazy enumerable +**When capacity is sufficient + +### Measured Benchmark Results + +Real-world measurements from `RebalanceFlowBenchmarks` demonstrate the allocation tradeoffs: + +**Fixed Span Behavior (BaseSpanSize=100, 10 rebalance operations):** +- Snapshot: ~224KB allocated +- CopyOnRead: ~92KB allocated +- **CopyOnRead advantage: 2.4x lower allocation** + +**Fixed Span Behavior (BaseSpanSize=10,000, 10 rebalance operations):** +- Snapshot: ~16.5MB allocated (with Gen2 GC pressure) +- CopyOnRead: ~2.5MB allocated +- **CopyOnRead advantage: 6.6x lower allocation, reduced LOH pressure** + +**Growing Span Behavior (BaseSpanSize=100, span increases 100 per iteration):** +- Snapshot: ~967KB allocated +- CopyOnRead: ~560KB allocated +- **CopyOnRead maintains 1.7x advantage even under dynamic growth** + +**Key Observations:** +1. **Consistent allocation advantage**: CopyOnRead shows 2-6x lower allocations across all scenarios +2. **Baseline execution time**: ~1.05-1.07s (dominated by 1s total SynchronousDataSource delay) +3. **LOH impact**: Snapshot mode triggers Gen2 collections at BaseSpanSize=10,000 +4. **Buffer reuse**: CopyOnRead amortizes capacity growth, reducing steady-state allocations + +These results validate the design philosophy: CopyOnRead trades per-read allocation cost for dramatically reduced rematerialization overhead. + +For complete benchmark details, see [Benchmark Suite README](../benchmarks/SlidingWindowCache.Benchmarks/README.md). + +--- + +## Implementation Details: Staging Buffer Pattern + +### Why Two Buffers? + +Consider cache expansion during user request: + +```csharp +// Current cache: [100, 110] +var currentData = cache.ToRangeData(); // Lazy IEnumerable over _activeStorage + +// User requests: [105, 115] +var extendedData = await ExtendCacheAsync(currentData, [105, 115]); +// extendedData.Data = Concat(currentData.Data, newlyFetched) +// This is a LINQ chain still tied to _activeStorage! + +cache.Rematerialize(extendedData); +// OLD (BROKEN): _storage.Clear() → corrupts LINQ chain mid-enumeration +// NEW (CORRECT): _stagingBuffer.Clear() → _activeStorage remains immutable +``` + +### Buffer Swap Invariants + +1. **Active storage is immutable during reads**: Never mutated until swap +2. **Staging buffer is write-only during rematerialization**: Cleared, filled, swapped +3. **Swap is atomic**: Single tuple assignment +4. **Buffers never shrink**: Capacity grows monotonically, amortizing allocation cost + +### Memory Growth Example + +``` +Initial state: +_activeStorage: capacity=0, count=0 +_stagingBuffer: capacity=0, count=0 + +After Rematerialize([100 items]): +_activeStorage: capacity=128, count=100 ← List grew to 128 +_stagingBuffer: capacity=0, count=0 + +After Rematerialize([150 items]): +_activeStorage: capacity=256, count=150 ← Reused capacity=128, grew to 256 +_stagingBuffer: capacity=128, count=100 ← Swapped, now has old capacity + +After Rematerialize([120 items]): +_activeStorage: capacity=128, count=120 ← Reused capacity=128, no allocation! +_stagingBuffer: capacity=256, count=150 ← Swapped + +Steady state reached: Both buffers have sufficient capacity, no more allocations +``` + +--- + +## Alignment with System Invariants + +The staging buffer pattern directly supports key system invariants: + +### Invariant A.3.8 - Cache Mutation Rules + +- **Cold Start**: Staging buffer safely materializes initial cache +- **Expansion**: Active storage stays immutable while LINQ chains enumerate it +- **Replacement**: Atomic swap ensures clean transition + +### Invariant A.3.9a - Cache Contiguity + +- Single-pass enumeration into staging buffer maintains contiguity +- No partial or gapped states + +### Invariant B.11-12 - Atomic Consistency + +- Tuple swap `(_activeStorage, _stagingBuffer) = (_stagingBuffer, _activeStorage)` is atomic +- Range update happens after swap, completing atomic change +- No intermediate inconsistent states + +### Invariant B.15 - Cancellation Safety + +- If rematerialization is cancelled mid-AddRange, staging buffer is abandoned +- Active storage remains unchanged, cache stays consistent + +--- + +## Testing Considerations + +### Snapshot Storage Tests + +```csharp +[Fact] +public async Task SnapshotMode_ZeroAllocationReads() +{ + var options = new WindowCacheOptions(readMode: UserCacheReadMode.Snapshot); + var cache = new WindowCache(...); + + var data1 = await cache.GetDataAsync(Range.Closed(100, 110), ct); + var data2 = await cache.GetDataAsync(Range.Closed(105, 115), ct); + + // Both reads return slices over same underlying array (until rematerialization) + // No allocations for reads +} +``` + +### CopyOnRead Storage Tests + +```csharp +[Fact] +public async Task CopyOnReadMode_CorrectDuringExpansion() +{ + var options = new WindowCacheOptions(readMode: UserCacheReadMode.CopyOnRead); + var cache = new WindowCache(...); + + // First request: [100, 110] + await cache.GetDataAsync(Range.Closed(100, 110), ct); + + // Second request: [105, 115] (intersects, triggers expansion) + var data = await cache.GetDataAsync(Range.Closed(105, 115), ct); + + // Staging buffer pattern ensures correctness: + // - Old storage remains immutable during LINQ enumeration + // - New data materialized into staging buffer + // - Buffers swapped atomically + + VerifyDataMatchesRange(data, Range.Closed(105, 115)); +} +``` + +--- + +## Summary + +- **Snapshot**: Fast reads, expensive rematerialization, best for read-heavy workloads +- **CopyOnRead with Staging Buffer**: Fast rematerialization, expensive reads, best for rematerialization-heavy + workloads +- **Composition**: Combine both strategies in multi-level caches for optimal performance +- **Staging Buffer**: Critical correctness pattern preventing enumeration corruption + +Choose based on your access pattern. When in doubt, start with Snapshot and profile. diff --git a/global.json b/global.json new file mode 100644 index 0000000..2ddda36 --- /dev/null +++ b/global.json @@ -0,0 +1,7 @@ +{ + "sdk": { + "version": "8.0.0", + "rollForward": "latestMinor", + "allowPrerelease": false + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache.WasmValidation/README.md b/src/SlidingWindowCache.WasmValidation/README.md new file mode 100644 index 0000000..6230699 --- /dev/null +++ b/src/SlidingWindowCache.WasmValidation/README.md @@ -0,0 +1,65 @@ +# SlidingWindowCache.WasmValidation + +## Purpose + +This project is a **WebAssembly compilation validation target** for the SlidingWindowCache library. It is **NOT** a demo application, test project, or runtime sample. + +## Goal + +The sole purpose of this project is to ensure that the SlidingWindowCache library successfully compiles for the `net8.0-browser` target framework, validating WebAssembly compatibility. + +## What This Is NOT + +- ❌ **Not a demo** - Does not demonstrate usage patterns or best practices +- ❌ **Not a test project** - Contains no assertions, test framework, or test execution logic +- ❌ **Not a runtime validation** - Code is not intended to be executed in CI/CD or production +- ❌ **Not a sample** - Does not showcase real-world scenarios or advanced features + +## What This IS + +- ✅ **Compile-only validation** - Successful build proves WebAssembly compatibility +- ✅ **CI/CD compatibility check** - Ensures library can target browser environments +- ✅ **Minimal API usage** - Instantiates core types to validate no platform-incompatible APIs are used + +## Implementation + +The project contains minimal code that: + +1. Implements a simple `IDataSource` +2. Instantiates `WindowCache` +3. Calls `GetDataAsync` with a `Range` +4. Uses `ReadOnlyMemory` return type +5. Calls `WaitForIdleAsync` for completeness + +All code uses deterministic, synchronous-friendly patterns suitable for compile-time validation. + +## Build Validation + +To validate WebAssembly compatibility: + +```bash +dotnet build src/SlidingWindowCache.WasmValidation/SlidingWindowCache.WasmValidation.csproj +``` + +A successful build confirms that: +- All SlidingWindowCache public APIs compile for `net8.0-browser` +- No platform-specific APIs incompatible with WebAssembly are used +- Intervals.NET dependencies are WebAssembly-compatible + +## Target Framework + +- **Framework**: `net8.0-browser` +- **SDK**: Microsoft.NET.Sdk +- **Output**: Class library (no entry point) + +## Dependencies + +Matches the main library dependencies: +- Intervals.NET.Data (0.0.1) +- Intervals.NET.Domain.Default (0.0.2) +- Intervals.NET.Domain.Extensions (0.0.3) +- SlidingWindowCache (project reference) + +## Integration with CI/CD + +This project should be included in CI build matrices to automatically validate WebAssembly compatibility on every build. Any compilation failure indicates a breaking change for browser-targeted applications. diff --git a/src/SlidingWindowCache.WasmValidation/SlidingWindowCache.WasmValidation.csproj b/src/SlidingWindowCache.WasmValidation/SlidingWindowCache.WasmValidation.csproj new file mode 100644 index 0000000..751b075 --- /dev/null +++ b/src/SlidingWindowCache.WasmValidation/SlidingWindowCache.WasmValidation.csproj @@ -0,0 +1,21 @@ + + + + net8.0-browser + enable + enable + false + Library + + + + + + + + + + + + + diff --git a/src/SlidingWindowCache.WasmValidation/WasmCompilationValidator.cs b/src/SlidingWindowCache.WasmValidation/WasmCompilationValidator.cs new file mode 100644 index 0000000..842b0f5 --- /dev/null +++ b/src/SlidingWindowCache.WasmValidation/WasmCompilationValidator.cs @@ -0,0 +1,84 @@ +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; +using SlidingWindowCache.Public.Dto; + +namespace SlidingWindowCache.WasmValidation; + +/// +/// Minimal IDataSource implementation for WebAssembly compilation validation. +/// This is NOT a demo or test - it exists purely to ensure the library compiles for net8.0-browser. +/// +internal sealed class SimpleDataSource : IDataSource +{ + public Task> FetchAsync(Range range, CancellationToken cancellationToken) + { + // Generate deterministic sequential data for the range + // Range.Start and Range.End are RangeValue, use implicit conversion to int + var start = range.Start.Value; + var end = range.End.Value; + var data = Enumerable.Range(start, end - start + 1); + return Task.FromResult(data); + } + + public Task>> FetchAsync( + IEnumerable> ranges, + CancellationToken cancellationToken + ) + { + var chunks = ranges.Select(r => + { + var start = r.Start.Value; + var end = r.End.Value; + return new RangeChunk(r, Enumerable.Range(start, end - start + 1)); + }); + return Task.FromResult(chunks); + } +} + +/// +/// WebAssembly compilation validator for SlidingWindowCache. +/// This static class validates that the library can compile for net8.0-browser. +/// It is NOT intended to be executed - successful compilation is the validation. +/// +public static class WasmCompilationValidator +{ + /// + /// Validates that WindowCache can be instantiated and used with all required types. + /// This method demonstrates minimal usage of the public API to ensure WebAssembly compatibility. + /// + public static async Task ValidateCompilation() + { + // Create a simple data source + var dataSource = new SimpleDataSource(); + + // Create domain (IntegerFixedStepDomain from Intervals.NET) + var domain = new IntegerFixedStepDomain(); + + // Configure cache options + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2 + ); + + // Instantiate WindowCache with concrete generic types + var cache = new WindowCache( + dataSource, + domain, + options + ); + + // Perform a GetDataAsync call with Range from Intervals.NET + var range = Intervals.NET.Factories.Range.Closed(0, 10); + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // Wait for background operations to complete + await cache.WaitForIdleAsync(); + + // Compilation successful if this code builds for net8.0-browser + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/Planning/ProportionalRangePlanner.cs b/src/SlidingWindowCache/Core/Planning/ProportionalRangePlanner.cs new file mode 100644 index 0000000..2306ea3 --- /dev/null +++ b/src/SlidingWindowCache/Core/Planning/ProportionalRangePlanner.cs @@ -0,0 +1,34 @@ +using Intervals.NET; +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Infrastructure.Extensions; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Core.Planning; + +internal readonly struct ProportionalRangePlanner + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly WindowCacheOptions _options; + private readonly TDomain _domain; + + public ProportionalRangePlanner(WindowCacheOptions options, TDomain domain) + { + _options = options; + _domain = domain; + } + + public Range Plan(Range requested) + { + var size = requested.Span(_domain); + + var left = size.Value * _options.LeftCacheSize; + var right = size.Value * _options.RightCacheSize; + + return requested.Expand( + domain: _domain, + left: (long)left, + right: (long)right + ); + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/Rebalance/Decision/RebalanceDecision.cs b/src/SlidingWindowCache/Core/Rebalance/Decision/RebalanceDecision.cs new file mode 100644 index 0000000..3005244 --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Decision/RebalanceDecision.cs @@ -0,0 +1,39 @@ +using Intervals.NET; + +namespace SlidingWindowCache.Core.Rebalance.Decision; + +/// +/// Represents the result of a rebalance decision evaluation. +/// +/// The type representing the range boundaries. +internal readonly struct RebalanceDecision + where TRange : IComparable +{ + /// + /// Gets a value indicating whether rebalance execution should proceed. + /// + public bool ShouldExecute { get; } + + /// + /// Gets the desired cache range if execution is allowed, otherwise null. + /// + public Range? DesiredRange { get; } + + private RebalanceDecision(bool shouldExecute, Range? desiredRange) + { + ShouldExecute = shouldExecute; + DesiredRange = desiredRange; + } + + /// + /// Creates a decision to skip rebalance execution. + /// + public static RebalanceDecision Skip() => new(false, null); + + /// + /// Creates a decision to execute rebalance with the specified desired range. + /// + /// The target cache range for rebalancing. + public static RebalanceDecision Execute(Range desiredRange) => + new(true, desiredRange); +} diff --git a/src/SlidingWindowCache/Core/Rebalance/Decision/RebalanceDecisionEngine.cs b/src/SlidingWindowCache/Core/Rebalance/Decision/RebalanceDecisionEngine.cs new file mode 100644 index 0000000..5fa6344 --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Decision/RebalanceDecisionEngine.cs @@ -0,0 +1,61 @@ +using Intervals.NET; +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Core.Planning; +using SlidingWindowCache.Core.Rebalance.Intent; + +namespace SlidingWindowCache.Core.Rebalance.Decision; + +/// +/// Evaluates whether rebalance execution is required based on cache geometry policy. +/// This component lives strictly in the background execution context and is never +/// invoked directly by the User Path. +/// +/// The type representing the range boundaries. +/// The type representing the domain of the ranges. +/// +/// Execution Context: Background / ThreadPool +/// Visibility: Not visible to User Path, invoked only by RebalanceScheduler +/// Characteristics: Pure, deterministic, side-effect free +/// +internal sealed class RebalanceDecisionEngine + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly ThresholdRebalancePolicy _policy; + private readonly ProportionalRangePlanner _planner; + + public RebalanceDecisionEngine( + ThresholdRebalancePolicy policy, + ProportionalRangePlanner planner) + { + _policy = policy; + _planner = planner; + } + + /// + /// Evaluates whether rebalance execution should proceed based on the requested range + /// and current cache state. + /// + /// The range requested by the user. + /// The range within which no rebalancing should occur. + /// A decision indicating whether to execute rebalance and the desired range if applicable. + public RebalanceDecision ShouldExecuteRebalance( + Range requestedRange, + Range? noRebalanceRange) + { + // Decision Path D1: Check NoRebalanceRange (fast path) + // If RequestedRange is fully contained within NoRebalanceRange, skip rebalancing + if (noRebalanceRange.HasValue && + !_policy.ShouldRebalance(noRebalanceRange.Value, requestedRange)) + { + return RebalanceDecision.Skip(); + } + + // Decision Path D2/D3: Compute DesiredCacheRange + var desiredRange = _planner.Plan(requestedRange); + + // Decision is to execute - IntentManager will check if desiredRange differs from current + // before actually invoking the executor + return RebalanceDecision.Execute(desiredRange); + } +} diff --git a/src/SlidingWindowCache/Core/Rebalance/Execution/CacheDataExtensionService.cs b/src/SlidingWindowCache/Core/Rebalance/Execution/CacheDataExtensionService.cs new file mode 100644 index 0000000..241ab47 --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Execution/CacheDataExtensionService.cs @@ -0,0 +1,151 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Data.Extensions; +using Intervals.NET.Domain.Abstractions; +using Intervals.NET.Extensions; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Dto; + +namespace SlidingWindowCache.Core.Rebalance.Execution; + +/// +/// Fetches missing data from the data source to extend the cache. +/// Does not perform trimming - that's the responsibility of the caller based on their context. +/// +/// +/// The type representing the range boundaries. Must implement . +/// +/// +/// The type of data being cached. +/// +/// +/// The type representing the domain of the ranges. Must implement . +/// +internal sealed class CacheDataExtensionService + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly IDataSource _dataSource; + private readonly TDomain _domain; + private readonly ICacheDiagnostics _cacheDiagnostics; + + /// + /// Initializes a new instance of the class. + /// + /// + /// The data source from which to fetch data. + /// + /// + /// The domain defining the range characteristics. + /// + /// + /// The diagnostics interface for recording cache operation metrics and events. + /// + public CacheDataExtensionService( + IDataSource dataSource, + TDomain domain, + ICacheDiagnostics cacheDiagnostics + ) + { + _dataSource = dataSource; + _domain = domain; + _cacheDiagnostics = cacheDiagnostics; + } + + /// + /// Extends the cache to cover the requested range by fetching only missing data segments. + /// Preserves all existing cached data without trimming. + /// + /// The current cached data. + /// The requested range that needs to be covered by the cache. + /// Cancellation token. + /// + /// Extended cache containing all existing data plus newly fetched data to cover the requested range. + /// + /// + /// Operation: Extends cache to cover requested range (NO trimming of existing data). + /// Use case: User requests (GetDataAsync) where we want to preserve all cached data for future rebalancing. + /// Optimization: Only fetches data not already in cache (partial cache hit optimization). + /// Note: This is an internal component that does not perform input validation or short-circuit checks. + /// All parameters are assumed to be pre-validated by the caller. Duplicating validation here would be unnecessary overhead. + /// Example: + /// + /// Cache: [100, 200], Requested: [150, 250] + /// - Already cached: [150, 200] + /// - Missing (fetched): (200, 250] + /// - Result: [100, 250] (ALL existing data preserved + newly fetched) + /// + /// Later rebalance to [50, 300] can reuse [100, 250] without re-fetching! + /// + /// + public async Task> ExtendCacheAsync( + RangeData currentCache, + Range requested, + CancellationToken ct + ) + { + _cacheDiagnostics.DataSourceFetchMissingSegments(); + + // Step 1: Calculate which ranges are missing + var missingRanges = CalculateMissingRanges(currentCache.Range, requested); + + // Step 2: Fetch the missing data from data source + var fetchedResults = await _dataSource.FetchAsync(missingRanges, ct); + + // Step 3: Union fetched data with current cache + return UnionAll(currentCache, fetchedResults, _domain); + } + + /// + /// Calculates which ranges are missing from the current cache to cover the requested range. + /// Uses range intersection and subtraction to determine gaps. + /// + /// The range currently covered by the cache. + /// The range that needs to be covered. + /// + /// An enumerable of missing ranges that need to be fetched, or null if there's no intersection + /// (meaning the entire requested range needs to be fetched). + /// + private IEnumerable> CalculateMissingRanges( + Range currentRange, + Range requestedRange + ) + { + var intersection = currentRange.Intersect(requestedRange); + + if (intersection.HasValue) + { + _cacheDiagnostics.CacheExpanded(); + // Calculate the missing segments using range subtraction + return requestedRange.Except(intersection.Value); + } + + _cacheDiagnostics.CacheReplaced(); + // No overlap - indicate that entire requested range is missing + // This signals to fetch the whole requested range without trying to calculate missing segments, as they are all missing. + return [requestedRange]; + } + + /// + /// Combines the existing cached data with the newly fetched data, + /// ensuring that the resulting range data is correctly merged and consistent with the domain. + /// + private static RangeData UnionAll( + RangeData current, + IEnumerable> rangeChunks, + TDomain domain + ) + { + // Combine existing data with fetched data + foreach (var (range, data) in rangeChunks) + { + // It is important to call Union on the current range data to overwrite outdated + // intersected segments with the newly fetched data, ensuring that the most up-to-date + // information is retained in the cache. + current = current.Union(data.ToRangeData(range, domain))!; + } + + return current; + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/Rebalance/Execution/RebalanceExecutor.cs b/src/SlidingWindowCache/Core/Rebalance/Execution/RebalanceExecutor.cs new file mode 100644 index 0000000..1dbc78a --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Execution/RebalanceExecutor.cs @@ -0,0 +1,130 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Core.Rebalance.Intent; +using SlidingWindowCache.Core.State; +using SlidingWindowCache.Infrastructure.Instrumentation; + +namespace SlidingWindowCache.Core.Rebalance.Execution; + +/// +/// Executes rebalance operations by fetching missing data, merging with existing cache, +/// and trimming to the desired range. This is the sole component responsible for cache normalization. +/// +/// The type representing the range boundaries. +/// The type of data being cached. +/// The type representing the domain of the ranges. +/// +/// Execution Context: Background / ThreadPool +/// Characteristics: Asynchronous, cancellable, heavyweight +/// Responsibility: Cache normalization (expand, trim, recompute NoRebalanceRange) +/// +internal sealed class RebalanceExecutor + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly CacheState _state; + private readonly CacheDataExtensionService _cacheExtensionService; + private readonly ThresholdRebalancePolicy _rebalancePolicy; + private readonly ICacheDiagnostics _cacheDiagnostics; + + public RebalanceExecutor( + CacheState state, + CacheDataExtensionService cacheExtensionService, + ThresholdRebalancePolicy rebalancePolicy, + ICacheDiagnostics cacheDiagnostics + ) + { + _state = state; + _cacheExtensionService = cacheExtensionService; + _rebalancePolicy = rebalancePolicy; + _cacheDiagnostics = cacheDiagnostics; + } + + /// + /// Executes rebalance by normalizing the cache to the desired range. + /// This is the ONLY component that mutates cache state (single-writer architecture). + /// + /// The intent with data that was actually assembled in UserPath and the requested range. + /// The target cache range to normalize to. + /// Cancellation token to support cancellation at all stages. + /// A task representing the asynchronous rebalance operation. + /// + /// + /// This executor is the sole writer of all cache state including: + /// + /// Cache.Rematerialize (cache data and range) + /// LastRequested field + /// NoRebalanceRange field + /// + /// + /// + /// The delivered data from the intent is used as the authoritative base source, + /// avoiding duplicate fetches and ensuring consistency with what the user received. + /// + /// + public async Task ExecuteAsync( + Intent intent, + Range desiredRange, + CancellationToken cancellationToken) + { + // Use delivered data as the base - this is what the user received + var baseRangeData = intent.AvailableRangeData; + + // Check if desired range equals delivered data range (Decision Path D2) + // This is a final check before expensive I/O operations + if (baseRangeData.Range == desiredRange) + { + _cacheDiagnostics.RebalanceSkippedSameRange(); + // Even though ranges match, we still need to update cache state since + // User Path no longer writes to cache. Use delivered data directly. + UpdateCacheState(baseRangeData, intent.RequestedRange); + return; + } + + // Cancellation check after decision but before expensive I/O + // Satisfies Invariant 34a: "Rebalance Execution MUST yield to User Path requests immediately" + cancellationToken.ThrowIfCancellationRequested(); + + // Phase 1: Extend delivered data to cover desired range (fetch only truly missing data) + // Use delivered data as base instead of current cache to ensure consistency + var extended = await _cacheExtensionService.ExtendCacheAsync(baseRangeData, desiredRange, cancellationToken); + + // Cancellation check after I/O but before mutation + // If User Path cancelled us, don't apply the rebalance result + cancellationToken.ThrowIfCancellationRequested(); + + // Phase 2: Trim to desired range (rebalancing-specific: discard data outside desired range) + baseRangeData = extended[desiredRange]; + + // Final cancellation check before applying mutation + // Ensures we don't apply obsolete rebalance results + cancellationToken.ThrowIfCancellationRequested(); + + // Phase 3: Apply cache state mutations + UpdateCacheState(baseRangeData, intent.RequestedRange); + + _cacheDiagnostics.RebalanceExecutionCompleted(); + } + + /// + /// Updates cache state with rebalanced data. This is the ONLY location where cache mutations occur. + /// SINGLE-WRITER: Only Rebalance Execution writes to cache state. + /// + /// The normalized data to write to cache. + /// The original range requested by the user, used to update LastRequested field. + private void UpdateCacheState(RangeData normalizedData, Range requestedRange) + { + // Phase 1: Update the cache with the rebalanced data (atomic mutation) + // SINGLE-WRITER: This is the ONLY place where cache state is written + _state.Cache.Rematerialize(normalizedData); + + // Phase 2: Update LastRequested to the original user's requested range + // SINGLE-WRITER: Only Rebalance Execution writes to LastRequested + _state.LastRequested = requestedRange; + + // Phase 3: Update the no-rebalance range to prevent unnecessary rebalancing + // SINGLE-WRITER: Only Rebalance Execution writes to NoRebalanceRange + _state.NoRebalanceRange = _rebalancePolicy.GetNoRebalanceRange(_state.Cache.Range); + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/Rebalance/Intent/Intent.cs b/src/SlidingWindowCache/Core/Rebalance/Intent/Intent.cs new file mode 100644 index 0000000..ad7b0fd --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Intent/Intent.cs @@ -0,0 +1,30 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Domain.Abstractions; + +namespace SlidingWindowCache.Core.Rebalance.Intent; + +/// +/// Represents the intent to rebalance the cache based on a requested range and the currently available range data. +/// +/// +/// The range requested by the user that triggered the rebalance evaluation. This is the range for which the user is seeking data. +/// +/// +/// The current range of data available in the cache along with its associated data and domain information. This represents the state of the cache before any rebalance execution. +/// +/// +/// The type representing the range boundaries. Must implement to allow for range comparisons and calculations. +/// +/// +/// The type of data being cached. This is the type of the elements stored within the ranges in the cache. +/// +/// +/// The type representing the domain of the ranges. Must implement to provide necessary domain-specific operations for range calculations and validations. +/// +public record Intent( + Range RequestedRange, + RangeData AvailableRangeData +) + where TRange : IComparable + where TDomain : IRangeDomain; \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/Rebalance/Intent/IntentController.cs b/src/SlidingWindowCache/Core/Rebalance/Intent/IntentController.cs new file mode 100644 index 0000000..2bfc257 --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Intent/IntentController.cs @@ -0,0 +1,206 @@ +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Core.Rebalance.Decision; +using SlidingWindowCache.Core.Rebalance.Execution; +using SlidingWindowCache.Core.State; +using SlidingWindowCache.Infrastructure.Instrumentation; + +namespace SlidingWindowCache.Core.Rebalance.Intent; + +/// +/// Manages the lifecycle of rebalance intents. +/// This is the Intent Controller component within the Rebalance Intent Manager actor. +/// +/// The type representing the range boundaries. +/// The type of data being cached. +/// The type representing the domain of the ranges. +/// +/// Architectural Model: +/// +/// The Rebalance Intent Manager is a single logical ACTOR in the system architecture. +/// Internally, it is decomposed into two cooperating components: +/// +/// +/// IntentController (this class) - Intent lifecycle management +/// RebalanceScheduler - Timing, debounce, pipeline orchestration +/// +/// Intent Controller Responsibilities: +/// +/// Receives rebalance intents on every user access +/// Owns intent identity and versioning (CancellationTokenSource) +/// Cancels and invalidates obsolete intents +/// Exposes cancellation interface to User Path +/// +/// Explicit Non-Responsibilities: +/// +/// ❌ Does NOT perform scheduling or timing logic (Scheduler's responsibility) +/// ❌ Does NOT decide whether rebalance is logically required (DecisionEngine's job) +/// ❌ Does NOT orchestrate execution pipeline (Scheduler's responsibility) +/// +/// Lock-Free Implementation: +/// +/// ✅ Thread-safe using for atomic operations +/// ✅ No locks, no lock statements, no mutexes +/// ✅ No race conditions - atomic field replacement ensures correctness +/// ✅ Guaranteed progress - non-blocking operations +/// ✅ Validated under concurrent load by ConcurrencyStabilityTests +/// +/// +internal sealed class IntentController + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly RebalanceScheduler _scheduler; + private readonly ICacheDiagnostics _cacheDiagnostics; + + /// + /// The current rebalance cancellation token source. + /// Represents the identity and lifecycle of the latest rebalance intent. + /// + private CancellationTokenSource? _currentIntentCts; + + /// + /// Initializes a new instance of the class. + /// + /// The cache state. + /// The decision engine for rebalance logic. + /// The executor for performing rebalance operations. + /// The debounce delay before executing rebalance. + /// The diagnostics interface for recording cache metrics and events related to rebalance intents. + /// + /// This constructor composes the Intent Controller with the Execution Scheduler + /// to form the complete Rebalance Intent Manager actor. + /// + public IntentController( + CacheState state, + RebalanceDecisionEngine decisionEngine, + RebalanceExecutor executor, + TimeSpan debounceDelay, + ICacheDiagnostics cacheDiagnostics + ) + { + _cacheDiagnostics = cacheDiagnostics; + // Compose with scheduler component + _scheduler = new RebalanceScheduler( + state, + decisionEngine, + executor, + debounceDelay, + cacheDiagnostics + ); + } + + /// + /// Cancels any pending or ongoing rebalance execution. + /// This method is called by the User Path to ensure exclusive cache access + /// before performing cache mutations (satisfies Invariant A.1-0a). + /// + /// + /// + /// This method is synchronous and returns immediately after signaling cancellation. + /// The background rebalance task will handle the cancellation asynchronously. + /// + /// + /// User Path never waits for rebalance to fully complete - it just ensures + /// the cancellation signal is sent before proceeding with its own mutations. + /// + /// Lock-Free Implementation: + /// + /// Uses atomic exchange to clear the current intent + /// without requiring locks. This ensures thread-safety and prevents race conditions + /// while maintaining non-blocking semantics. + /// + /// + public void CancelPendingRebalance() + { + var cancellationTokenSource = Interlocked.Exchange(ref _currentIntentCts, null); + + if (cancellationTokenSource == null) + { + return; + } + + if (cancellationTokenSource.IsCancellationRequested) + { + return; + } + + cancellationTokenSource.Cancel(); + cancellationTokenSource.Dispose(); + } + + /// + /// Publishes a rebalance intent triggered by a user request. + /// This method is fire-and-forget and returns immediately. + /// + /// The data that was actually delivered to the user for the requested range. + /// + /// + /// Every user access produces a rebalance intent. This method implements the + /// Intent Controller pattern by: + /// + /// Invalidating the previous intent (if any) + /// Creating a new intent with unique identity (CancellationTokenSource) + /// Delegating to scheduler for debounce and execution + /// + /// + /// + /// The intent contains both the requested range and the assembled data. + /// This allows Rebalance Execution to use the assembled data as an authoritative source, + /// avoiding duplicate fetches and ensuring consistency. + /// + /// + /// This implements Invariant C.18: "Any previously created rebalance intent is obsolete + /// after a new intent is generated." + /// + /// + /// Responsibility separation: Intent lifecycle management is handled here, + /// while scheduling/execution is delegated to RebalanceScheduler. + /// + /// + public void PublishIntent(Intent intent) + { + var newCts = new CancellationTokenSource(); + var intentToken = newCts.Token; + + // SAFE PATH - + // Atomically replace the current intent with the new one and capture the old one for cancellation + var oldCts = Interlocked.Exchange(ref _currentIntentCts, newCts); + + // Invalidate previous intent (Invariant C.18: "Any previously created rebalance intent is obsolete") + if (oldCts is not null) + { + oldCts.Cancel(); + oldCts.Dispose(); + } + // SAFE PATH END + + // Delegate to scheduler for debounce and execution + // The scheduler owns timing, debounce, and pipeline orchestration + _scheduler.ScheduleRebalance(intent, intentToken); + + _cacheDiagnostics.RebalanceIntentPublished(); + } + + /// + /// Waits for the latest scheduled rebalance background Task to complete. + /// Provides deterministic synchronization for infrastructure scenarios. + /// + /// + /// Maximum time to wait for idle state. Defaults to 30 seconds. + /// + /// A Task that completes when the background rebalance has finished. + /// + /// Idle Proxy Responsibility: + /// + /// This method delegates to which owns + /// the background Task lifecycle. IntentController acts as a proxy, exposing the idle + /// synchronization mechanism without implementing Task tracking itself. + /// + /// + /// This is an infrastructure API useful for testing, graceful shutdown, health checks, + /// and other scenarios requiring synchronization with background rebalance operations. + /// Intent lifecycle and cancellation logic remain unchanged. + /// + /// + public Task WaitForIdleAsync(TimeSpan? timeout = null) => _scheduler.WaitForIdleAsync(timeout); +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/Rebalance/Intent/RebalanceScheduler.cs b/src/SlidingWindowCache/Core/Rebalance/Intent/RebalanceScheduler.cs new file mode 100644 index 0000000..0011b8b --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Intent/RebalanceScheduler.cs @@ -0,0 +1,286 @@ +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Core.Rebalance.Decision; +using SlidingWindowCache.Core.Rebalance.Execution; +using SlidingWindowCache.Core.State; +using SlidingWindowCache.Infrastructure.Instrumentation; + +namespace SlidingWindowCache.Core.Rebalance.Intent; + +/// +/// Responsible for scheduling and executing rebalance operations in the background. +/// This is the Execution Scheduler component within the Rebalance Intent Manager actor. +/// +/// The type representing the range boundaries. +/// The type of data being cached. +/// The type representing the domain of the ranges. +/// +/// Architectural Role: +/// +/// This component is the Execution Scheduler within the larger Rebalance Intent Manager actor. +/// It works in tandem with IntentController to form a complete +/// rebalance management system. +/// +/// Responsibilities: +/// +/// Debounce delay and delayed execution +/// Ensures at most one rebalance execution is active +/// Executes rebalance asynchronously in background thread pool +/// Checks intent validity before execution starts +/// Propagates cancellation to executor +/// Orchestrates DecisionEngine → Executor pipeline +/// +/// Explicit Non-Responsibilities: +/// +/// ❌ Does NOT decide whether rebalance is logically required (DecisionEngine's job) +/// ❌ Does NOT own intent identity or versioning (IntentManager's job) +/// +/// +internal sealed class RebalanceScheduler + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly CacheState _state; + private readonly RebalanceDecisionEngine _decisionEngine; + private readonly RebalanceExecutor _executor; + private readonly TimeSpan _debounceDelay; + private readonly ICacheDiagnostics _cacheDiagnostics; + + /// + /// Tracks the latest scheduled rebalance background Task for deterministic idle synchronization. + /// Used by WaitForIdleAsync() to provide race-free infrastructure API for testing, graceful shutdown, + /// and health checks. This field exists in all builds to support the public WaitForIdleAsync() API. + /// Memory overhead: one Task reference per cache instance. + /// + private Task _idleTask = Task.CompletedTask; + + /// + /// Initializes a new instance of the class. + /// + /// The cache state. + /// The decision engine for rebalance logic. + /// The executor for performing rebalance operations. + /// The debounce delay before executing rebalance. + /// The diagnostics interface for recording rebalance-related metrics and events. + public RebalanceScheduler( + CacheState state, + RebalanceDecisionEngine decisionEngine, + RebalanceExecutor executor, + TimeSpan debounceDelay, + ICacheDiagnostics cacheDiagnostics + ) + { + _state = state; + _decisionEngine = decisionEngine; + _executor = executor; + _debounceDelay = debounceDelay; + _cacheDiagnostics = cacheDiagnostics; + } + + /// + /// Schedules a rebalance operation to execute after the debounce delay. + /// Checks intent validity before starting execution. + /// + /// The intent with data that was actually assembled in UserPath and the requested range. + /// Cancellation token for this specific intent (owned by IntentManager). + /// + /// + /// This method is fire-and-forget. It schedules execution in the background thread pool + /// and returns immediately. + /// + /// + /// The scheduler ensures single-flight execution through the intent cancellation token. + /// When a new intent arrives, the Intent Controller cancels the previous token, causing + /// any pending or executing rebalance to be cancelled. + /// + /// + public void ScheduleRebalance(Intent intent, CancellationToken intentToken) + { + // Fire-and-forget: schedule execution in background thread pool + // Fixing ambiguous invocation by explicitly specifying the type for Task.Run + var backgroundTask = Task.Run(async () => + { + try + { + await ExecuteAfterAsync( + executePipelineAsync: () => ExecutePipelineAsync(intent, intentToken), + intentToken: intentToken + ); + } + catch (OperationCanceledException) + { + // Expected when intent is cancelled or superseded + // This is normal behavior, not an error + _cacheDiagnostics.RebalanceIntentCancelled(); + } + catch (Exception) + { + // All other exceptions are already recorded via RebalanceExecutionFailed + // They bubble up from ExecutePipelineAsync and are swallowed here to prevent + // unhandled task exceptions from crashing the application. + // + // ⚠️ CRITICAL: Applications MUST subscribe to RebalanceExecutionFailed events + // and implement appropriate error handling (logging, alerting, monitoring). + // Ignoring this event means silent failures in background operations. + } + }, CancellationToken.None); + // NOTE: Do NOT pass intentToken to Task.Run ^ - it should only be used inside the lambda + // to ensure the try-catch properly handles all OperationCanceledExceptions + + // Track the latest background task for deterministic idle synchronization + // This supports the public WaitForIdleAsync() infrastructure API + _idleTask = backgroundTask; + } + + /// + /// Executes the provided function after a debounce delay, checking intent validity before execution. + /// + /// + /// The asynchronous function to execute after the debounce delay. This typically encapsulates the entire + /// decision and execution pipeline for rebalance. It receives the delivered data and intent token as context. + /// The function should respect the intentToken for cancellation to ensure timely yielding to new intents. + /// + /// + /// The cancellation token associated with the current intent. This token is used to implement single-flight execution and intent invalidation. + /// If this token is cancelled during the debounce delay, the execution will be aborted and the pipeline will not start. If the token is cancelled during execution, the pipeline should respond to cancellation as soon as possible to yield to new intents. + /// This token is owned and managed by the Intent Manager, which creates a new token for each intent and cancels the previous one when a new intent is published. + /// + private async Task ExecuteAfterAsync(Func executePipelineAsync, CancellationToken intentToken) + { + // Debounce delay: wait before executing + // This can be cancelled if a new intent arrives during the delay + await Task.Delay(_debounceDelay, intentToken); + + // Intent validity check: discard if cancelled during debounce + // This implements Invariant C.20: "If intent becomes obsolete before execution begins, execution must not start" + intentToken.ThrowIfCancellationRequested(); + + // Execute the provided function + await executePipelineAsync(); + } + + /// + /// Executes the decision-execution pipeline in the background. + /// + /// The intent with data that was actually assembled in UserPath and the requested range. + /// Cancellation token to support cancellation. + /// + /// Pipeline Flow: + /// + /// Check if intent is still valid (cancellation check) + /// Invoke DecisionEngine to determine if rebalance is needed + /// If needed, invoke Executor to perform rebalance using delivered data + /// + /// + private async Task ExecutePipelineAsync(Intent intent, + CancellationToken cancellationToken) + { + // Final cancellation check before decision logic + // Ensures we don't do work for an obsolete intent + if (cancellationToken.IsCancellationRequested) + { + _cacheDiagnostics.RebalanceIntentCancelled(); + return; + } + + // Step 1: Invoke DecisionEngine (pure decision logic) + // This checks NoRebalanceRange and computes DesiredCacheRange + var decision = _decisionEngine.ShouldExecuteRebalance( + requestedRange: intent.RequestedRange, + noRebalanceRange: _state.NoRebalanceRange + ); + + // Step 2: If decision says skip, return early (no-op) + if (!decision.ShouldExecute) + { + _cacheDiagnostics.RebalanceSkippedNoRebalanceRange(); + return; + } + + _cacheDiagnostics.RebalanceExecutionStarted(); + + // Step 3: If execution is allowed, invoke Executor with delivered data + // The executor will use delivered data as authoritative source, merge with existing cache, + // expand to desired range, trim excess, and update cache state + try + { + await _executor.ExecuteAsync(intent, decision.DesiredRange!.Value, cancellationToken); + } + catch (OperationCanceledException) + { + _cacheDiagnostics.RebalanceExecutionCancelled(); + throw; + } + catch (Exception ex) + { + // Record failure for diagnostic tracking + // WARNING: This is a fire-and-forget background operation failure + // Applications MUST monitor RebalanceExecutionFailed events and implement + // appropriate error handling (logging, alerting, etc.) + _cacheDiagnostics.RebalanceExecutionFailed(ex); + throw; + } + } + + /// + /// Waits for the latest scheduled rebalance background Task to complete. + /// Provides deterministic synchronization without relying on instrumentation counters. + /// + /// + /// Maximum time to wait for idle state. Defaults to 30 seconds. + /// Throws if the Task does not stabilize within this period. + /// + /// A Task that completes when the background rebalance has finished. + /// + /// Infrastructure API: + /// + /// This method provides deterministic synchronization with background rebalance operations. + /// It is useful for testing, graceful shutdown, health checks, integration scenarios, + /// and any situation requiring coordination with cache background work. + /// + /// Observe-and-Stabilize Pattern: + /// + /// Read current _idleTask via Volatile.Read (safe observation) + /// Await the observed Task + /// Re-check if _idleTask changed (new rebalance scheduled) + /// Loop until Task reference stabilizes and completes + /// + /// + /// This ensures that no rebalance execution is running when the method returns, + /// even under concurrent intent cancellation and rescheduling. + /// + /// + /// + /// Thrown if the background Task does not stabilize within the specified timeout. + /// + public async Task WaitForIdleAsync(TimeSpan? timeout = null) + { + var maxWait = timeout ?? TimeSpan.FromSeconds(30); + var stopwatch = System.Diagnostics.Stopwatch.StartNew(); + + while (stopwatch.Elapsed < maxWait) + { + // Observe current idle task (Volatile.Read ensures visibility) + var observedTask = Volatile.Read(ref _idleTask); + + // Await the observed task + await observedTask; + + // Check if _idleTask changed while we were waiting + var currentTask = Volatile.Read(ref _idleTask); + + if (ReferenceEquals(observedTask, currentTask)) + { + // Task reference stabilized and completed - we're idle + return; + } + + // Task changed - a new rebalance was scheduled, loop again + } + + // Timeout - provide diagnostic information + var finalTask = Volatile.Read(ref _idleTask); + throw new TimeoutException( + $"WaitForIdleAsync() timed out after {maxWait.TotalSeconds:F1}s. " + + $"Final task state: {finalTask.Status}"); + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/Rebalance/Intent/ThresholdRebalancePolicy.cs b/src/SlidingWindowCache/Core/Rebalance/Intent/ThresholdRebalancePolicy.cs new file mode 100644 index 0000000..2b925fc --- /dev/null +++ b/src/SlidingWindowCache/Core/Rebalance/Intent/ThresholdRebalancePolicy.cs @@ -0,0 +1,30 @@ +using Intervals.NET; +using Intervals.NET.Domain.Abstractions; +using Intervals.NET.Extensions; +using SlidingWindowCache.Infrastructure.Extensions; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Core.Rebalance.Intent; + +internal readonly struct ThresholdRebalancePolicy + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly WindowCacheOptions _options; + private readonly TDomain _domain; + + public ThresholdRebalancePolicy(WindowCacheOptions options, TDomain domain) + { + _options = options; + _domain = domain; + } + + public bool ShouldRebalance(Range noRebalanceRange, Range requested) => + !noRebalanceRange.Contains(requested); + + public Range? GetNoRebalanceRange(Range cacheRange) => cacheRange.ExpandByRatio( + domain: _domain, + leftRatio: -(_options.LeftThreshold ?? 0), // Negate to shrink + rightRatio: -(_options.RightThreshold ?? 0) // Negate to shrink + ); +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/State/CacheState.cs b/src/SlidingWindowCache/Core/State/CacheState.cs new file mode 100644 index 0000000..e1e223c --- /dev/null +++ b/src/SlidingWindowCache/Core/State/CacheState.cs @@ -0,0 +1,65 @@ +using Intervals.NET; +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Infrastructure.Storage; +using SlidingWindowCache.Public; + +namespace SlidingWindowCache.Core.State; + +/// +/// Encapsulates the mutable state of a window cache. +/// This class is shared between and its internal +/// rebalancing components, providing clear ownership semantics. +/// +/// +/// The type representing the range boundaries. Must implement . +/// +/// +/// The type of data being cached. +/// +/// +/// The type representing the domain of the ranges. Must implement . +/// +internal sealed class CacheState + where TRange : IComparable + where TDomain : IRangeDomain +{ + /// + /// The current cached data along with its range. + /// + public ICacheStorage Cache { get; } + + /// + /// The last requested range that triggered a cache access. + /// + /// + /// SINGLE-WRITER: Only Rebalance Execution Path may write to this field. + /// User Path is read-only with respect to cache state. + /// + public Range? LastRequested { get; internal set; } + + /// + /// The range within which no rebalancing should occur. + /// It is based on configured threshold policies. + /// + /// + /// SINGLE-WRITER: Only Rebalance Execution Path may write to this field. + /// This field is recomputed after each successful rebalance execution. + /// + public Range? NoRebalanceRange { get; internal set; } + + /// + /// Gets the domain defining the range characteristics for this cache instance. + /// + public TDomain Domain { get; } + + /// + /// Initializes a new instance of the class. + /// + /// The cache storage implementation. + /// The domain defining the range characteristics. + public CacheState(ICacheStorage cacheStorage, TDomain domain) + { + Cache = cacheStorage; + Domain = domain; + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Core/UserPath/UserRequestHandler.cs b/src/SlidingWindowCache/Core/UserPath/UserRequestHandler.cs new file mode 100644 index 0000000..f08f7ea --- /dev/null +++ b/src/SlidingWindowCache/Core/UserPath/UserRequestHandler.cs @@ -0,0 +1,201 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Data.Extensions; +using Intervals.NET.Domain.Abstractions; +using Intervals.NET.Extensions; +using SlidingWindowCache.Core.Rebalance.Execution; +using SlidingWindowCache.Core.Rebalance.Intent; +using SlidingWindowCache.Core.State; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; + +namespace SlidingWindowCache.Core.UserPath; + +/// +/// Handles user requests synchronously, serving data from cache or data source. +/// This is the Fast Path Actor that operates in the User Thread. +/// +/// The type representing the range boundaries. +/// The type of data being cached. +/// The type representing the domain of the ranges. +/// +/// Execution Context: User Thread +/// Critical Contract: +/// +/// Every user access produces a rebalance intent. +/// The UserRequestHandler NEVER invokes decision logic. +/// +/// Responsibilities: +/// +/// Handles user requests synchronously +/// Decides how to serve RequestedRange (from cache, from IDataSource, or mixed) +/// Updates LastRequestedRange and CacheData/CurrentCacheRange only to cover RequestedRange +/// Triggers rebalance intent (fire-and-forget) +/// Never blocks on rebalance +/// +/// Explicit Non-Responsibilities: +/// +/// ❌ NEVER checks NoRebalanceRange (belongs to DecisionEngine) +/// ❌ NEVER computes DesiredCacheRange (belongs to GeometryPolicy) +/// ❌ NEVER decides whether to rebalance (belongs to DecisionEngine) +/// ❌ No cache normalization +/// ❌ No trimming or shrinking +/// +/// +internal sealed class UserRequestHandler + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly CacheState _state; + private readonly CacheDataExtensionService _cacheExtensionService; + private readonly IntentController _intentManager; + private readonly IDataSource _dataSource; + private readonly ICacheDiagnostics _cacheDiagnostics; + + /// + /// Initializes a new instance of the class. + /// + /// The cache state. + /// The cache data fetcher for extending cache coverage. + /// The intent controller for publishing rebalance intents. + /// The data source to request missing data from. + /// The diagnostics interface for recording cache metrics and events related to user requests. + public UserRequestHandler(CacheState state, + CacheDataExtensionService cacheExtensionService, + IntentController intentManager, + IDataSource dataSource, + ICacheDiagnostics cacheDiagnostics + ) + { + _state = state; + _cacheExtensionService = cacheExtensionService; + _intentManager = intentManager; + _dataSource = dataSource; + _cacheDiagnostics = cacheDiagnostics; + } + + /// + /// Handles a user request for the specified range. + /// + /// The range requested by the user. + /// A cancellation token to cancel the operation. + /// + /// A task that represents the asynchronous operation. The task result contains a + /// of data for the specified range from the materialized cache. + /// + /// + /// This method implements the User Path logic (READ-ONLY with respect to cache state): + /// + /// Cancel any pending/ongoing rebalance (Invariant A.0: User Path priority) + /// Check if requested range is fully or partially covered by cache + /// Fetch missing data from IDataSource as needed + /// Materialize assembled data to array + /// Return ReadOnlyMemory to user immediately + /// Publish rebalance intent with delivered data (fire-and-forget) + /// + /// CRITICAL: User Path is READ-ONLY + /// + /// User Path NEVER writes to cache state. All cache mutations are performed exclusively + /// by Rebalance Execution Path (single-writer architecture). The User Path: + /// + /// ✅ May READ from cache + /// ✅ May READ from IDataSource + /// ❌ NEVER writes to Cache (no Rematerialize calls) + /// ❌ NEVER writes to LastRequested + /// ❌ NEVER writes to NoRebalanceRange + /// + /// + /// + public async ValueTask> HandleRequestAsync( + Range requestedRange, + CancellationToken cancellationToken) + { + // CRITICAL: Cancel any pending/ongoing rebalance FIRST (Invariant A.0: User Path priority) + // This ensures rebalance execution doesn't interfere even though User Path no longer mutates + _intentManager.CancelPendingRebalance(); + + // Check if cache is cold (never used) - use ToRangeData to detect empty cache + var cacheStorage = _state.Cache; + var isColdStart = !_state.LastRequested.HasValue; + + RangeData? assembledData = null; + + try + { + if (isColdStart) + { + // Scenario 1: Cold Start + // Cache has never been populated - fetch data ONLY for requested range + _cacheDiagnostics.DataSourceFetchSingleRange(); + assembledData = (await _dataSource.FetchAsync(requestedRange, cancellationToken)) + .ToRangeData(requestedRange, _state.Domain); + + _cacheDiagnostics.UserRequestFullCacheMiss(); + + return new ReadOnlyMemory(assembledData.Data.ToArray()); + } + + var fullyInCache = cacheStorage.Range.Contains(requestedRange); + + if (fullyInCache) + { + // Scenario 2: Full Cache Hit + // All requested data is available in cache - read from cache (no IDataSource call) + assembledData = cacheStorage.ToRangeData(); + + _cacheDiagnostics.UserRequestFullCacheHit(); + + // Return a requested range data using the cache storage's Read method, which may return a view or a copy depending on the strategy + return cacheStorage.Read(requestedRange); + } + + var hasOverlap = cacheStorage.Range.Overlaps(requestedRange); + + if (hasOverlap) + { + // Scenario 3: Partial Cache Hit + // RequestedRange intersects CurrentCacheRange - read from cache and fetch missing parts + // ExtendCacheAsync will compute missing ranges and fetch only those parts + // NOTE: The usage of storage.Read doesn't make sense here because we need to assemble a contiguous range that may require concatenating multiple segments (cached + fetched) + assembledData = await _cacheExtensionService.ExtendCacheAsync( + cacheStorage.ToRangeData(), + requestedRange, + cancellationToken + ); + + _cacheDiagnostics.UserRequestPartialCacheHit(); + + return new ReadOnlyMemory(assembledData[requestedRange].Data.ToArray()); + } + + // Scenario 4: Full Cache Miss (Non-intersecting Jump) + // RequestedRange does NOT intersect CurrentCacheRange + // Fetch ONLY the requested range from IDataSource + // NOTE: The logic is similar to cold start + _cacheDiagnostics.DataSourceFetchSingleRange(); + assembledData = (await _dataSource.FetchAsync(requestedRange, cancellationToken)) + .ToRangeData(requestedRange, _state.Domain); + + _cacheDiagnostics.UserRequestFullCacheMiss(); + + return new ReadOnlyMemory(assembledData.Data.ToArray()); + } + finally + { + // If assembledData is NULL, it means an exception was thrown during data retrieval (either from cache or data source). + // Publishing intent doesn't make sense, the possibly redundant rebalance triggered by this failure will simply fail again during execution or next user request. + // So, exception should be catched and handled before proceeding to publish intent. + if (assembledData is not null) + { + // Create new Intent + var intent = new Intent(requestedRange, assembledData); + + // Publish rebalance intent with assembled data range (fire-and-forget) + // Rebalance Execution will use this as the authoritative source + _intentManager.PublishIntent(intent); + + _cacheDiagnostics.UserRequestServed(); + } + } + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Infrastructure/Extensions/IntervalsNetDomainExtensions.cs b/src/SlidingWindowCache/Infrastructure/Extensions/IntervalsNetDomainExtensions.cs new file mode 100644 index 0000000..337a361 --- /dev/null +++ b/src/SlidingWindowCache/Infrastructure/Extensions/IntervalsNetDomainExtensions.cs @@ -0,0 +1,116 @@ +using Intervals.NET; +using Intervals.NET.Domain.Abstractions; + +namespace SlidingWindowCache.Infrastructure.Extensions; + +/// +/// Provides domain-agnostic extension methods that work with any IRangeDomain type. +/// These methods dispatch to the appropriate Fixed or Variable extension methods based on the runtime domain type. +/// +/// +/// +/// While Intervals.NET separates fixed-step and variable-step extension methods into different namespaces +/// to enforce explicit performance semantics at the API level, cache scenarios benefit from flexibility: +/// in-memory O(N) step counting (microseconds) is negligible compared to data source I/O (milliseconds to seconds). +/// +/// +/// These extensions enable the cache to work with any domain type, whether fixed-step or variable-step, +/// by dispatching to the appropriate implementation at runtime. +/// +/// +internal static class IntervalsNetDomainExtensions +{ + /// + /// Calculates the number of discrete steps within a range for any domain type. + /// + /// The type representing range boundaries. + /// The domain type (can be fixed or variable-step). + /// The range to measure. + /// The domain defining discrete steps. + /// The number of discrete steps, or infinity if unbounded. + /// + /// Performance: O(1) for fixed-step domains, O(N) for variable-step domains. + /// The O(N) cost is acceptable because it represents in-memory computation that is orders of magnitude + /// faster than data source I/O operations. + /// + /// + /// Thrown when the domain does not implement either IFixedStepDomain or IVariableStepDomain. + /// + public static RangeValue Span(this Range range, TDomain domain) + where TRange : IComparable + where TDomain : IRangeDomain => domain switch + { + IFixedStepDomain fixedDomain => Intervals.NET.Domain.Extensions.Fixed.RangeDomainExtensions.Span(range, fixedDomain), + IVariableStepDomain variableDomain => Intervals.NET.Domain.Extensions.Variable.RangeDomainExtensions.Span(range, variableDomain), + _ => throw new NotSupportedException( + $"Domain type {domain.GetType().Name} must implement either IFixedStepDomain or IVariableStepDomain.") + }; + + /// + /// Expands a range by a specified number of steps on each side for any domain type. + /// + /// The type representing range boundaries. + /// The domain type (can be fixed or variable-step). + /// The range to expand. + /// The domain defining discrete steps. + /// Number of steps to expand on the left. + /// Number of steps to expand on the right. + /// The expanded range. + /// + /// Performance: O(1) for fixed-step domains, O(N) for variable-step domains. + /// The O(N) cost is acceptable because it represents in-memory computation that is orders of magnitude + /// faster than data source I/O operations. + /// + /// + /// Thrown when the domain does not implement either IFixedStepDomain or IVariableStepDomain. + /// + public static Range Expand( + this Range range, + TDomain domain, + long left, + long right) + where TRange : IComparable + where TDomain : IRangeDomain => domain switch + { + IFixedStepDomain fixedDomain => Intervals.NET.Domain.Extensions.Fixed.RangeDomainExtensions.Expand( + range, fixedDomain, left, right), + IVariableStepDomain variableDomain => Intervals.NET.Domain.Extensions.Variable.RangeDomainExtensions + .Expand(range, variableDomain, left, right), + _ => throw new NotSupportedException( + $"Domain type {domain.GetType().Name} must implement either IFixedStepDomain or IVariableStepDomain.") + }; + + /// + /// Expands or shrinks a range by a ratio of its size for any domain type. + /// + /// The type representing range boundaries. + /// The domain type (can be fixed or variable-step). + /// The range to modify. + /// The domain defining discrete steps. + /// Ratio to expand/shrink the left boundary (negative shrinks). + /// Ratio to expand/shrink the right boundary (negative shrinks). + /// The modified range. + /// + /// Performance: O(1) for fixed-step domains, O(N) for variable-step domains. + /// The O(N) cost is acceptable because it represents in-memory computation that is orders of magnitude + /// faster than data source I/O operations. + /// + /// + /// Thrown when the domain does not implement either IFixedStepDomain or IVariableStepDomain. + /// + public static Range ExpandByRatio( + this Range range, + TDomain domain, + double leftRatio, + double rightRatio) + where TRange : IComparable + where TDomain : IRangeDomain => domain switch + { + IFixedStepDomain fixedDomain => Intervals.NET.Domain.Extensions.Fixed.RangeDomainExtensions + .ExpandByRatio(range, fixedDomain, leftRatio, rightRatio), + IVariableStepDomain variableDomain => Intervals.NET.Domain.Extensions.Variable.RangeDomainExtensions + .ExpandByRatio(range, variableDomain, leftRatio, rightRatio), + _ => throw new NotSupportedException( + $"Domain type {domain.GetType().Name} must implement either IFixedStepDomain or IVariableStepDomain.") + }; +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Infrastructure/Instrumentation/EventCounterCacheDiagnostics.cs b/src/SlidingWindowCache/Infrastructure/Instrumentation/EventCounterCacheDiagnostics.cs new file mode 100644 index 0000000..b6254ce --- /dev/null +++ b/src/SlidingWindowCache/Infrastructure/Instrumentation/EventCounterCacheDiagnostics.cs @@ -0,0 +1,129 @@ +using System.Diagnostics; + +namespace SlidingWindowCache.Infrastructure.Instrumentation; + +/// +/// Default implementation of that uses thread-safe counters to track cache events and metrics. +/// +public class EventCounterCacheDiagnostics : ICacheDiagnostics +{ + private int _userRequestServed; + private int _cacheExpanded; + private int _cacheReplaced; + private int _rebalanceIntentPublished; + private int _rebalanceIntentCancelled; + private int _rebalanceExecutionStarted; + private int _rebalanceExecutionCompleted; + private int _rebalanceExecutionCancelled; + private int _rebalanceSkippedNoRebalanceRange; + private int _rebalanceSkippedSameRange; + private int _userRequestFullCacheHit; + private int _userRequestPartialCacheHit; + private int _userRequestFullCacheMiss; + private int _dataSourceFetchSingleRange; + private int _dataSourceFetchMissingSegments; + private int _rebalanceExecutionFailed; + + public int UserRequestServed => _userRequestServed; + public int CacheExpanded => _cacheExpanded; + public int CacheReplaced => _cacheReplaced; + public int UserRequestFullCacheHit => _userRequestFullCacheHit; + public int UserRequestPartialCacheHit => _userRequestPartialCacheHit; + public int UserRequestFullCacheMiss => _userRequestFullCacheMiss; + public int DataSourceFetchSingleRange => _dataSourceFetchSingleRange; + public int DataSourceFetchMissingSegments => _dataSourceFetchMissingSegments; + public int RebalanceIntentPublished => _rebalanceIntentPublished; + public int RebalanceIntentCancelled => _rebalanceIntentCancelled; + public int RebalanceExecutionStarted => _rebalanceExecutionStarted; + public int RebalanceExecutionCompleted => _rebalanceExecutionCompleted; + public int RebalanceExecutionCancelled => _rebalanceExecutionCancelled; + public int RebalanceSkippedNoRebalanceRange => _rebalanceSkippedNoRebalanceRange; + public int RebalanceSkippedSameRange => _rebalanceSkippedSameRange; + public int RebalanceExecutionFailed => _rebalanceExecutionFailed; + + /// + void ICacheDiagnostics.CacheExpanded() => Interlocked.Increment(ref _cacheExpanded); + + /// + void ICacheDiagnostics.CacheReplaced() => Interlocked.Increment(ref _cacheReplaced); + + /// + void ICacheDiagnostics.DataSourceFetchMissingSegments() => + Interlocked.Increment(ref _dataSourceFetchMissingSegments); + + /// + void ICacheDiagnostics.DataSourceFetchSingleRange() => Interlocked.Increment(ref _dataSourceFetchSingleRange); + + /// + void ICacheDiagnostics.RebalanceExecutionCancelled() => Interlocked.Increment(ref _rebalanceExecutionCancelled); + + /// + void ICacheDiagnostics.RebalanceExecutionCompleted() => Interlocked.Increment(ref _rebalanceExecutionCompleted); + + /// + void ICacheDiagnostics.RebalanceExecutionStarted() => Interlocked.Increment(ref _rebalanceExecutionStarted); + + /// + void ICacheDiagnostics.RebalanceIntentCancelled() => Interlocked.Increment(ref _rebalanceIntentCancelled); + + /// + void ICacheDiagnostics.RebalanceIntentPublished() => Interlocked.Increment(ref _rebalanceIntentPublished); + + /// + void ICacheDiagnostics.RebalanceSkippedNoRebalanceRange() => + Interlocked.Increment(ref _rebalanceSkippedNoRebalanceRange); + + /// + void ICacheDiagnostics.RebalanceSkippedSameRange() => Interlocked.Increment(ref _rebalanceSkippedSameRange); + + /// + void ICacheDiagnostics.RebalanceExecutionFailed(Exception ex) + { + Interlocked.Increment(ref _rebalanceExecutionFailed); + + // ⚠️ WARNING: This default implementation only writes to Debug output! + // For production use, you MUST create a custom implementation that: + // 1. Logs to your logging framework (e.g., ILogger, Serilog, NLog) + // 2. Includes full exception details (message, stack trace, inner exceptions) + // 3. Considers alerting/monitoring for repeated failures + // + // Example: + // _logger.LogError(ex, "Cache rebalance execution failed. Cache may not be optimally sized."); + Debug.WriteLine($"⚠️ Rebalance execution failed: {ex}"); + } + + /// + void ICacheDiagnostics.UserRequestFullCacheHit() => Interlocked.Increment(ref _userRequestFullCacheHit); + + /// + void ICacheDiagnostics.UserRequestFullCacheMiss() => Interlocked.Increment(ref _userRequestFullCacheMiss); + + /// + void ICacheDiagnostics.UserRequestPartialCacheHit() => Interlocked.Increment(ref _userRequestPartialCacheHit); + + /// + void ICacheDiagnostics.UserRequestServed() => Interlocked.Increment(ref _userRequestServed); + + /// + /// Resets all counters to zero. Use this before each test to ensure clean state. + /// + public void Reset() + { + _userRequestServed = 0; + _cacheExpanded = 0; + _cacheReplaced = 0; + _rebalanceIntentPublished = 0; + _rebalanceIntentCancelled = 0; + _rebalanceExecutionStarted = 0; + _rebalanceExecutionCompleted = 0; + _rebalanceExecutionCancelled = 0; + _rebalanceSkippedNoRebalanceRange = 0; + _rebalanceSkippedSameRange = 0; + _userRequestFullCacheHit = 0; + _userRequestPartialCacheHit = 0; + _userRequestFullCacheMiss = 0; + _dataSourceFetchSingleRange = 0; + _dataSourceFetchMissingSegments = 0; + _rebalanceExecutionFailed = 0; + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Infrastructure/Instrumentation/ICacheDiagnostics.cs b/src/SlidingWindowCache/Infrastructure/Instrumentation/ICacheDiagnostics.cs new file mode 100644 index 0000000..3683be4 --- /dev/null +++ b/src/SlidingWindowCache/Infrastructure/Instrumentation/ICacheDiagnostics.cs @@ -0,0 +1,219 @@ +namespace SlidingWindowCache.Infrastructure.Instrumentation; + +/// +/// Instance-based diagnostics interface for tracking cache behavioral events in DEBUG mode. +/// Mirrors the public API of CacheInstrumentationCounters to enable dependency injection. +/// Used for testing and verification of system invariants. +/// +public interface ICacheDiagnostics +{ + // ============================================================================ + // USER PATH COUNTERS + // ============================================================================ + + /// + /// Records a completed user request served by the User Path. + /// Called at the end of UserRequestHandler.HandleRequestAsync after data is returned to the user and intent is published. + /// Tracks completion of all user scenarios: cold start (U1), full cache hit (U2, U3), partial cache hit (U4), and full cache miss/jump (U5). + /// Location: UserRequestHandler.HandleRequestAsync (final step) + /// + void UserRequestServed(); + + /// + /// Records when cache extension analysis determines that expansion is needed (intersection exists). + /// Called during range analysis in CacheDataExtensionService.CalculateMissingRanges when determining + /// which segments need to be fetched. This indicates the cache WILL BE expanded, not that mutation occurred. + /// Note: This is called by the shared CacheDataExtensionService used by both User Path and Rebalance Path. + /// The actual cache mutation (Rematerialize) only happens in Rebalance Execution. + /// Location: CacheDataExtensionService.CalculateMissingRanges (when intersection exists) + /// Related: Invariant 9a (Cache Contiguity Rule) + /// + void CacheExpanded(); + + /// + /// Records when cache extension analysis determines that full replacement is needed (no intersection). + /// Called during range analysis in CacheDataExtensionService.CalculateMissingRanges when determining + /// that RequestedRange does NOT intersect CurrentCacheRange. This indicates cache WILL BE replaced, + /// not that mutation occurred. The actual cache mutation (Rematerialize) only happens in Rebalance Execution. + /// Note: This is called by the shared CacheDataExtensionService used by both User Path and Rebalance Path. + /// Location: CacheDataExtensionService.CalculateMissingRanges (when no intersection exists) + /// Related: Invariant 9a (Cache Contiguity Rule - forbids gaps) + /// + void CacheReplaced(); + + /// + /// Records a full cache hit where all requested data is available in cache without fetching from IDataSource. + /// Called when CurrentCacheRange fully contains RequestedRange, allowing direct read from cache. + /// Represents optimal performance path (User Scenarios U2, U3). + /// Location: UserRequestHandler.HandleRequestAsync (Scenario 2: Full Cache Hit) + /// + void UserRequestFullCacheHit(); + + /// + /// Records a partial cache hit where RequestedRange intersects CurrentCacheRange but is not fully contained. + /// Called when some data is available in cache and missing segments are fetched from IDataSource and merged. + /// Indicates efficient cache extension with partial reuse (User Scenario U4). + /// Location: UserRequestHandler.HandleRequestAsync (Scenario 3: Partial Cache Hit) + /// + void UserRequestPartialCacheHit(); + + /// + /// Records a full cache miss requiring complete fetch from IDataSource. + /// Called in two scenarios: cold start (no cache) or non-intersecting jump (cache exists but RequestedRange doesn't intersect). + /// Indicates most expensive path with no cache reuse (User Scenarios U1, U5). + /// Location: UserRequestHandler.HandleRequestAsync (Scenario 1: Cold Start, Scenario 4: Full Cache Miss) + /// + void UserRequestFullCacheMiss(); + + // ============================================================================ + // DATA SOURCE ACCESS COUNTERS + // ============================================================================ + + /// + /// Records a single-range fetch from IDataSource for a complete range. + /// Called in cold start or non-intersecting jump scenarios where the entire RequestedRange must be fetched as one contiguous range. + /// Indicates IDataSource.FetchAsync(Range) invocation for user-facing data assembly. + /// Location: UserRequestHandler.HandleRequestAsync (Scenarios 1 and 4: Cold Start and Non-intersecting Jump) + /// Related: User Path direct fetch operations + /// + void DataSourceFetchSingleRange(); + + /// + /// Records a missing-segments fetch from IDataSource during cache extension. + /// Called when extending cache to cover RequestedRange by fetching only the missing segments (gaps between RequestedRange and CurrentCacheRange). + /// Indicates IDataSource.FetchAsync(IEnumerable<Range>) invocation with computed missing ranges. + /// Location: CacheDataExtensionService.ExtendCacheAsync (partial cache hit optimization) + /// Related: User Scenario U4 and Rebalance Execution cache extension operations + /// + void DataSourceFetchMissingSegments(); + + // ============================================================================ + // REBALANCE INTENT LIFECYCLE COUNTERS + // ============================================================================ + + /// + /// Records publication of a rebalance intent by the User Path. + /// Called after UserRequestHandler publishes an intent containing delivered data to IntentController. + /// Every user request produces exactly one intent publication (fire-and-forget). + /// Location: IntentController.PublishIntent (after scheduler receives intent) + /// Related: Invariant A.3 (User Path is sole source of rebalance intent), Invariant 24e (Intent must contain delivered data) + /// Note: Intent publication does NOT guarantee execution (opportunistic behavior) + /// + void RebalanceIntentPublished(); + + /// + /// Records cancellation of a rebalance intent before or during execution. + /// Called when a new user request arrives and cancels the previous intent's CancellationToken, or when intent becomes obsolete during debounce delay. + /// Indicates single-flight execution pattern and priority enforcement (User Path cancels Rebalance). + /// Location: RebalanceScheduler (three scenarios: cancellation during debounce, cancellation before decision, cancellation during execution) + /// Related: Invariant A.0 (User Path priority), Invariant A.0a (User Request must cancel ongoing rebalance), Invariant C.20 (Obsolete intent must not start) + /// + void RebalanceIntentCancelled(); + + // ============================================================================ + // REBALANCE EXECUTION LIFECYCLE COUNTERS + // ============================================================================ + + /// + /// Records the start of rebalance execution after decision engine approves execution. + /// Called when DecisionEngine determines rebalance is necessary (RequestedRange outside NoRebalanceRange and DesiredCacheRange != CurrentCacheRange). + /// Indicates transition from Decision Path to Execution Path (Decision Scenario D3). + /// Location: RebalanceScheduler.ExecutePipelineAsync (after decision approval, before executor invocation) + /// Related: Invariant 28 (Rebalance triggered only if confirmed necessary) + /// + void RebalanceExecutionStarted(); + + /// + /// Records successful completion of rebalance execution. + /// Called after RebalanceExecutor successfully extends cache to DesiredCacheRange, trims excess data, and updates cache state. + /// Indicates cache normalization completed and state mutations applied (Rebalance Scenarios R1, R2). + /// Location: RebalanceExecutor.ExecuteAsync (final step after UpdateCacheState) + /// Related: Invariant 34 (Only Rebalance Execution writes to cache), Invariant 35 (Cache state update is atomic) + /// + void RebalanceExecutionCompleted(); + + /// + /// Records cancellation of rebalance execution due to a new user request or intent supersession. + /// Called when intentToken is cancelled during rebalance execution (after execution started but before completion). + /// Indicates User Path priority enforcement and single-flight execution (yielding to new requests). + /// Location: RebalanceScheduler.ExecutePipelineAsync (catch OperationCanceledException during execution) + /// Related: Invariant 34a (Rebalance Execution must yield to User Path immediately) + /// + void RebalanceExecutionCancelled(); + + // ============================================================================ + // REBALANCE SKIP OPTIMIZATION COUNTERS + // ============================================================================ + + /// + /// Records a rebalance skipped due to RequestedRange being within NoRebalanceRange. + /// Called when DecisionEngine determines rebalance is unnecessary because RequestedRange falls inside the no-rebalance threshold zone. + /// Indicates policy-based skip decision before expensive operations (Decision Scenario D1). + /// Location: RebalanceScheduler.ExecutePipelineAsync (after DecisionEngine returns ShouldExecute=false) + /// Related: Invariant D.26 (No rebalance if inside NoRebalanceRange), Invariant D.27 (Policy-based skip tracking) + /// + void RebalanceSkippedNoRebalanceRange(); + + /// + /// Records a rebalance skipped because CurrentCacheRange equals DesiredCacheRange. + /// Called when RebalanceExecutor detects that delivered data range already matches desired range, avoiding redundant I/O. + /// Indicates same-range optimization preventing unnecessary fetch operations (Decision Scenario D2). + /// Location: RebalanceExecutor.ExecuteAsync (before expensive I/O operations) + /// Related: Invariant D.27 (No rebalance if DesiredCacheRange == CurrentCacheRange), Invariant D.28 (Same-range optimization tracking) + /// + void RebalanceSkippedSameRange(); + + /// + /// Records a rebalance execution failure due to an exception during execution. + /// Called when an unhandled exception occurs during RebalanceExecutor.ExecuteAsync. + /// + /// + /// The exception that caused the rebalance execution to fail. This parameter provides details about the failure and can be used for logging and diagnostics. + /// + /// + /// ⚠️ CRITICAL: Applications MUST handle this event + /// + /// Rebalance operations execute in fire-and-forget background tasks. When an exception occurs, + /// the task catches it, records this event, and silently swallows the exception to prevent + /// application crashes from unhandled task exceptions. + /// + /// Consequences of ignoring this event: + /// + /// Silent failures in background operations + /// Cache may stop rebalancing without any visible indication + /// Degraded performance with no diagnostics + /// Data source errors may go unnoticed + /// + /// Recommended implementation: + /// + /// At minimum, log all RebalanceExecutionFailed events with full exception details. + /// Consider also implementing: + /// + /// + /// Structured logging with context (requested range, cache state) + /// Alerting for repeated failures (circuit breaker pattern) + /// Metrics tracking failure rate and exception types + /// Graceful degradation strategies (e.g., disable rebalancing after N failures) + /// + /// Example implementation: + /// + /// public class LoggingCacheDiagnostics : ICacheDiagnostics + /// { + /// private readonly ILogger _logger; + /// + /// public void RebalanceExecutionFailed(Exception ex) + /// { + /// _logger.LogError(ex, "Cache rebalance execution failed. Cache may not be optimally sized."); + /// // Optional: Increment error counter for monitoring + /// // Optional: Trigger alert if failure rate exceeds threshold + /// } + /// + /// // ...other methods... + /// } + /// + /// + /// Location: RebalanceScheduler.ExecutePipelineAsync (catch block around ExecuteAsync) + /// + /// + void RebalanceExecutionFailed(Exception ex); +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Infrastructure/Instrumentation/NoOpDiagnostics.cs b/src/SlidingWindowCache/Infrastructure/Instrumentation/NoOpDiagnostics.cs new file mode 100644 index 0000000..25713d0 --- /dev/null +++ b/src/SlidingWindowCache/Infrastructure/Instrumentation/NoOpDiagnostics.cs @@ -0,0 +1,87 @@ +namespace SlidingWindowCache.Infrastructure.Instrumentation; + +/// +/// No-op implementation of ICacheDiagnostics for production use where performance is critical and diagnostics are not needed. +/// +public class NoOpDiagnostics : ICacheDiagnostics +{ + /// + public void CacheExpanded() + { + } + + /// + public void CacheReplaced() + { + } + + /// + public void DataSourceFetchMissingSegments() + { + } + + /// + public void DataSourceFetchSingleRange() + { + } + + /// + public void RebalanceExecutionCancelled() + { + } + + /// + public void RebalanceExecutionCompleted() + { + } + + /// + public void RebalanceExecutionStarted() + { + } + + /// + public void RebalanceIntentCancelled() + { + } + + /// + public void RebalanceIntentPublished() + { + } + + /// + public void RebalanceSkippedNoRebalanceRange() + { + } + + /// + public void RebalanceSkippedSameRange() + { + } + + /// + public void RebalanceExecutionFailed(Exception ex) + { + } + + /// + public void UserRequestFullCacheHit() + { + } + + /// + public void UserRequestFullCacheMiss() + { + } + + /// + public void UserRequestPartialCacheHit() + { + } + + /// + public void UserRequestServed() + { + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Infrastructure/Storage/CopyOnReadStorage.cs b/src/SlidingWindowCache/Infrastructure/Storage/CopyOnReadStorage.cs new file mode 100644 index 0000000..19cc58f --- /dev/null +++ b/src/SlidingWindowCache/Infrastructure/Storage/CopyOnReadStorage.cs @@ -0,0 +1,194 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Data.Extensions; +using Intervals.NET.Domain.Abstractions; +using Intervals.NET.Extensions; +using SlidingWindowCache.Infrastructure.Extensions; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Infrastructure.Storage; + +/// +/// CopyOnRead strategy that stores data using a dual-buffer (staging buffer) pattern. +/// Uses two internal lists: one active storage for reads, one staging buffer for rematerialization. +/// +/// +/// The type representing the range boundaries. Must implement . +/// +/// +/// The type of data being cached. +/// +/// +/// The type representing the domain of the ranges. Must implement . +/// +/// +/// Dual-Buffer Staging Pattern: +/// +/// This storage maintains two internal lists: +/// +/// +/// _activeStorage - Immutable during reads, used for serving data +/// _stagingBuffer - Write-only during rematerialization, reused across operations +/// +/// Rematerialization Process: +/// +/// Clear staging buffer (preserves capacity) +/// Enumerate incoming range data into staging buffer (single-pass) +/// Atomically swap staging buffer with active storage +/// +/// +/// This ensures that active storage is never mutated during enumeration, preventing correctness issues +/// when range data is derived from the same storage (e.g., during cache expansion per Invariant A.3.8). +/// +/// Memory Behavior: +/// +/// Staging buffer may grow but never shrinks +/// Avoids repeated allocations by reusing capacity +/// No temporary arrays beyond the two buffers +/// Predictable allocation behavior for large sliding windows +/// +/// Read Behavior: +/// +/// Each read operation allocates a new array and copies data from active storage (copy-on-read semantics). +/// This is a trade-off for cheaper rematerialization compared to Snapshot mode. +/// +/// When to Use: +/// +/// Large sliding windows with frequent rematerialization +/// Infrequent reads relative to rematerialization +/// Scenarios where backing memory reuse is valuable +/// Multi-level cache composition (background layer feeding snapshot-based cache) +/// +/// +internal sealed class CopyOnReadStorage : ICacheStorage + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly TDomain _domain; + + // Active storage: immutable during reads, serves data to Read() operations + private List _activeStorage = []; + + // Staging buffer: write-only during rematerialization, reused across operations + // This buffer may grow but never shrinks, amortizing allocation cost + private List _stagingBuffer = []; + + /// + /// Initializes a new instance of the class. + /// + /// + /// The domain defining the range characteristics. + /// + public CopyOnReadStorage(TDomain domain) + { + _domain = domain; + } + + /// + public UserCacheReadMode Mode => UserCacheReadMode.CopyOnRead; + + /// + public Range Range { get; private set; } + + /// + /// + /// Staging Buffer Rematerialization: + /// + /// This method implements a dual-buffer pattern to satisfy Invariants A.3.8, B.11-12: + /// + /// + /// Clear staging buffer (preserves capacity for reuse) + /// Enumerate range data into staging buffer (single-pass, no double enumeration) + /// Atomically swap buffers: staging becomes active, old active becomes staging + /// + /// + /// Why this pattern? When contains data derived from + /// the same storage (e.g., during cache expansion via LINQ operations like Concat/Union), direct + /// mutation of active storage would corrupt the enumeration. The staging buffer ensures active + /// storage remains immutable during enumeration, satisfying Invariant A.3.9a (cache contiguity). + /// + /// + /// Memory efficiency: The staging buffer reuses capacity across rematerializations, + /// avoiding repeated allocations for large sliding windows. The buffer may grow but never shrinks, + /// amortizing allocation cost over time. + /// + /// + public void Rematerialize(RangeData rangeData) + { + // Clear staging buffer (preserves capacity for reuse) + _stagingBuffer.Clear(); + + // Single-pass enumeration: materialize incoming range data into staging buffer + // This is safe even if rangeData.Data is based on _activeStorage (e.g., LINQ chains during expansion) + // because we never mutate _activeStorage during enumeration + _stagingBuffer.AddRange(rangeData.Data); + + // Atomically swap buffers: staging becomes active, old active becomes staging for next use + // This swap is the only point where active storage is replaced, satisfying Invariant B.12 (atomic changes) + (_activeStorage, _stagingBuffer) = (_stagingBuffer, _activeStorage); + + // Update range to reflect new active storage (part of atomic change) + Range = rangeData.Range; + } + + /// + /// + /// Copy-on-Read Semantics: + /// + /// Each read allocates a new array and copies the requested data from active storage. + /// This is the trade-off for cheaper rematerialization: reads are more expensive, + /// but rematerialization avoids allocating a new backing array each time. + /// + /// + /// Active storage is immutable during this operation, ensuring correctness within + /// the single-consumer model (Invariant A.1-1: no concurrent execution). + /// + /// + public ReadOnlyMemory Read(Range range) + { + if (_activeStorage.Count == 0) + { + return ReadOnlyMemory.Empty; + } + + // Validate that the requested range is within the stored range + if (!Range.Contains(range)) + { + throw new ArgumentOutOfRangeException(nameof(range), + $"Requested range {range} is not contained within the cached range {Range}"); + } + + // Calculate the offset and length for the requested range + var startOffset = _domain.Distance(Range.Start.Value, range.Start.Value); + var length = (int)range.Span(_domain); + + // Validate bounds before accessing storage + if (startOffset < 0 || length < 0 || (int)startOffset + length > _activeStorage.Count) + { + throw new ArgumentOutOfRangeException(nameof(range), + $"Calculated offset {startOffset} and length {length} exceed storage bounds (storage count: {_activeStorage.Count})"); + } + + // Allocate a new array and copy the requested data (copy-on-read semantics) + var result = new TData[length]; + for (var i = 0; i < length; i++) + { + result[i] = _activeStorage[(int)startOffset + i]; + } + + return new ReadOnlyMemory(result); + } + + /// + /// + /// + /// Returns a representing + /// the current active storage. The returned data is a lazy enumerable over the active list. + /// + /// + /// This method is safe because active storage is immutable during reads and only replaced + /// atomically during rematerialization (Invariant B.12). + /// + /// + public RangeData ToRangeData() => _activeStorage.ToRangeData(Range, _domain); +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Infrastructure/Storage/ICacheStorage.cs b/src/SlidingWindowCache/Infrastructure/Storage/ICacheStorage.cs new file mode 100644 index 0000000..df50873 --- /dev/null +++ b/src/SlidingWindowCache/Infrastructure/Storage/ICacheStorage.cs @@ -0,0 +1,73 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Infrastructure.Storage; + +/// +/// Internal strategy interface for handling user cache read operations. +/// +/// +/// The type representing the range boundaries. Must implement . +/// +/// +/// The type of data being cached. +/// +/// +/// The type representing the domain of the ranges. Must implement . +/// +/// +/// This interface is an implementation detail of the window cache. +/// It represents behavior over internal state, not a public service. +/// +internal interface ICacheStorage + where TRange : IComparable + where TDomain : IRangeDomain +{ + /// + /// Gets the read mode this strategy implements. + /// + UserCacheReadMode Mode { get; } + + /// + /// Gets the current range of data stored in internal storage. + /// + Range Range { get; } + + /// + /// Rematerializes internal storage from the provided range data. + /// + /// + /// The range data to materialize into internal storage. + /// + /// + /// This method is called during cache initialization and rebalancing. + /// All elements from the range data are rewritten into internal storage. + /// + void Rematerialize(RangeData rangeData); + + /// + /// Reads data for the specified range from internal storage. + /// + /// + /// The range for which to retrieve data. + /// + /// + /// A containing the data for the specified range. + /// + /// + /// The behavior of this method depends on the strategy: + /// - Snapshot: Returns a view directly over internal array (zero allocations). + /// - CopyOnRead: Allocates a new array and copies the requested data. + /// + ReadOnlyMemory Read(Range range); + + /// + /// Converts the current internal storage state into a representation. + /// + /// + /// A representing the current state of internal storage. + /// + RangeData ToRangeData(); +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Infrastructure/Storage/SnapshotReadStorage.cs b/src/SlidingWindowCache/Infrastructure/Storage/SnapshotReadStorage.cs new file mode 100644 index 0000000..934d958 --- /dev/null +++ b/src/SlidingWindowCache/Infrastructure/Storage/SnapshotReadStorage.cs @@ -0,0 +1,73 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Data.Extensions; +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Infrastructure.Extensions; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Infrastructure.Storage; + +/// +/// Snapshot read strategy that stores data in a contiguous array for zero-allocation reads. +/// +/// +/// The type representing the range boundaries. Must implement . +/// +/// +/// The type of data being cached. +/// +/// +/// The type representing the domain of the ranges. Must implement . +/// +internal sealed class SnapshotReadStorage : ICacheStorage + where TRange : IComparable + where TDomain : IRangeDomain +{ + private readonly TDomain _domain; + private TData[] _storage = []; + + /// + /// Initializes a new instance of the class. + /// + /// + /// The domain defining the range characteristics. + /// + public SnapshotReadStorage(TDomain domain) + { + _domain = domain; + } + + /// + public UserCacheReadMode Mode => UserCacheReadMode.Snapshot; + + /// + public Range Range { get; private set; } + + /// + public void Rematerialize(RangeData rangeData) + { + // Always allocate a new array, even if the size is unchanged + // This is the trade-off of the Snapshot mode + Range = rangeData.Range; + _storage = rangeData.Data.ToArray(); + } + + /// + public ReadOnlyMemory Read(Range range) + { + if (_storage.Length == 0) + { + return ReadOnlyMemory.Empty; + } + + // Calculate the offset and length for the requested range + var startOffset = _domain.Distance(Range.Start.Value, range.Start.Value); + var length = (int)range.Span(_domain); + + // Return a view directly over the internal array - zero allocations + return new ReadOnlyMemory(_storage, (int)startOffset, length); + } + + /// + public RangeData ToRangeData() => _storage.ToRangeData(Range, _domain); +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Public/Configuration/UserCacheReadMode.cs b/src/SlidingWindowCache/Public/Configuration/UserCacheReadMode.cs new file mode 100644 index 0000000..020eea0 --- /dev/null +++ b/src/SlidingWindowCache/Public/Configuration/UserCacheReadMode.cs @@ -0,0 +1,52 @@ +namespace SlidingWindowCache.Public.Configuration; + +/// +/// Defines how materialized cache data is exposed to users. +/// +/// +/// The read mode determines the trade-offs between read performance, allocation behavior, +/// rebalance cost, and memory pressure. This mode is configured once at cache creation time +/// and cannot be changed at runtime. +/// +public enum UserCacheReadMode +{ + /// + /// Stores data in a contiguous array internally. + /// User reads return pointing directly to the internal array. + /// + /// + /// Advantages: + /// + /// Zero allocations on read operations + /// Fastest read performance + /// Ideal for read-heavy scenarios + /// + /// Disadvantages: + /// + /// Rebalance always requires allocating a new array (even if size is unchanged) + /// Large arrays may end up on the Large Object Heap (LOH) when size ≥ 85,000 bytes + /// Higher memory pressure during rebalancing + /// + /// + Snapshot, + + /// + /// Stores data in a growable structure (e.g., ) internally. + /// User reads allocate a new array for the requested range and return it as . + /// + /// + /// Advantages: + /// + /// Rebalance is cheaper and does not necessarily allocate large arrays + /// Significantly less memory pressure during rebalancing + /// Avoids LOH allocations in most cases + /// Ideal for memory-sensitive scenarios + /// + /// Disadvantages: + /// + /// Allocates a new array on every read operation + /// Slower read performance due to allocation and copying + /// + /// + CopyOnRead +} diff --git a/src/SlidingWindowCache/Public/Configuration/WindowCacheOptions.cs b/src/SlidingWindowCache/Public/Configuration/WindowCacheOptions.cs new file mode 100644 index 0000000..0d2fdcf --- /dev/null +++ b/src/SlidingWindowCache/Public/Configuration/WindowCacheOptions.cs @@ -0,0 +1,109 @@ +namespace SlidingWindowCache.Public.Configuration; + +/// +/// Options for configuring the behavior of the sliding window cache. +/// +public record WindowCacheOptions +{ + /// + /// Initializes a new instance of the class. + /// + /// The coefficient for the left cache size. + /// The coefficient for the right cache size. + /// + /// The read mode that determines how materialized cache data is exposed to users. + /// This can affect the performance and memory usage of the cache, + /// as well as the consistency guarantees provided to users. + /// + /// The left threshold percentage (optional). + /// The right threshold percentage (optional). + /// The debounce delay for rebalance operations (optional). + /// + /// Thrown when LeftCacheSize, RightCacheSize, LeftThreshold, or RightThreshold is less than 0. + /// + public WindowCacheOptions( + double leftCacheSize, + double rightCacheSize, + UserCacheReadMode readMode, + double? leftThreshold = null, + double? rightThreshold = null, + TimeSpan? debounceDelay = null + ) + { + if (leftCacheSize < 0) + { + throw new ArgumentOutOfRangeException(nameof(leftCacheSize), + "LeftCacheSize must be greater than or equal to 0."); + } + + if (rightCacheSize < 0) + { + throw new ArgumentOutOfRangeException(nameof(rightCacheSize), + "RightCacheSize must be greater than or equal to 0."); + } + + if (leftThreshold is < 0) + { + throw new ArgumentOutOfRangeException(nameof(leftThreshold), + "LeftThreshold must be greater than or equal to 0."); + } + + if (rightThreshold is < 0) + { + throw new ArgumentOutOfRangeException(nameof(rightThreshold), + "RightThreshold must be greater than or equal to 0."); + } + + LeftCacheSize = leftCacheSize; + RightCacheSize = rightCacheSize; + ReadMode = readMode; + LeftThreshold = leftThreshold; + RightThreshold = rightThreshold; + DebounceDelay = debounceDelay ?? TimeSpan.FromMilliseconds(100); + } + + /// + /// The coefficient to determine the size of the left cache relative to the requested range. + /// If requested range size is S, left cache size will be S * LeftCacheSize. + /// Can be set as 0 to disable left caching. Must be greater than or equal to 0 + /// + public double LeftCacheSize { get; } + + /// + /// The coefficient to determine the size of the right cache relative to the requested range. + /// If requested range size is S, right cache size will be S * RightCacheSize. + /// Can be set as 0 to disable right caching. Must be greater than or equal to 0 + /// + public double RightCacheSize { get; } + + /// + /// The amount of percents of the total cache size that must be exceeded to trigger a rebalance. + /// The total cache size is defined as the sum of the left, requested range, and right cache sizes. + /// Can be set as null to disable rebalance based on left threshold. If only one threshold is set, + /// rebalance will be triggered when that threshold is exceeded or end of the cached range is exceeded. + /// Must be greater than or equal to 0 + /// Example: 0.2 means 20% of total cache size. Means if the next requested range and the start of the range contains less than 20% of the total cache size, a rebalance will be triggered. + /// + public double? LeftThreshold { get; } + + /// + /// The amount of percents of the total cache size that must be exceeded to trigger a rebalance. + /// The total cache size is defined as the sum of the left, requested range, and right cache sizes. + /// Can be set as null to disable rebalance based on right threshold. If only one threshold is set, + /// rebalance will be triggered when that threshold is exceeded or start of the cached range is exceeded. + /// Must be greater than or equal to 0 + /// Example: 0.2 means 20% of total cache size. Means if the next requested range and the end of the range contains less than 20% of the total cache size, a rebalance will be triggered. + /// + public double? RightThreshold { get; } + + /// + /// The debounce delay for rebalance operations. + /// Default is TimeSpan.FromMilliseconds(100). + /// + public TimeSpan DebounceDelay { get; } + + /// + /// The read mode that determines how materialized cache data is exposed to users. + /// + public UserCacheReadMode ReadMode { get; } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Public/Dto/RangeChunk.cs b/src/SlidingWindowCache/Public/Dto/RangeChunk.cs new file mode 100644 index 0000000..2aee087 --- /dev/null +++ b/src/SlidingWindowCache/Public/Dto/RangeChunk.cs @@ -0,0 +1,9 @@ +using Intervals.NET; + +namespace SlidingWindowCache.Public.Dto; + +/// +/// Represents a chunk of data associated with a specific range. This is used to encapsulate the data fetched for a particular range in the sliding window cache. +/// +public record RangeChunk(Range Range, IEnumerable Data) + where TRangeType : IComparable; \ No newline at end of file diff --git a/src/SlidingWindowCache/Public/IDataSource.cs b/src/SlidingWindowCache/Public/IDataSource.cs new file mode 100644 index 0000000..2d8aef7 --- /dev/null +++ b/src/SlidingWindowCache/Public/IDataSource.cs @@ -0,0 +1,122 @@ +using Intervals.NET; +using SlidingWindowCache.Public.Dto; + +namespace SlidingWindowCache.Public; + +/// +/// Defines the contract for data sources used in the sliding window cache. +/// Implementations must provide a method to fetch data for a single range. +/// The batch fetching method has a default implementation that can be overridden for optimization. +/// +/// +/// The type representing range boundaries. Must implement . +/// +/// +/// The type of data being fetched. +/// +/// +/// Basic Implementation: +/// +/// public class MyDataSource : IDataSource<int, MyData> +/// { +/// public async Task<IEnumerable<MyData>> FetchAsync( +/// Range<int> range, +/// CancellationToken ct) +/// { +/// // Fetch data for single range +/// return await Database.QueryAsync(range, ct); +/// } +/// +/// // Batch method uses default parallel implementation automatically +/// } +/// +/// Optimized Batch Implementation: +/// +/// public class OptimizedDataSource : IDataSource<int, MyData> +/// { +/// public async Task<IEnumerable<MyData>> FetchAsync( +/// Range<int> range, +/// CancellationToken ct) +/// { +/// return await Database.QueryAsync(range, ct); +/// } +/// +/// // Override for true batch optimization (single DB query) +/// public async Task<IEnumerable<RangeChunk<int, MyData>>> FetchAsync( +/// IEnumerable<Range<int>> ranges, +/// CancellationToken ct) +/// { +/// // Single database query for all ranges - much more efficient! +/// return await Database.QueryMultipleRangesAsync(ranges, ct); +/// } +/// } +/// +/// +public interface IDataSource where TRangeType : IComparable +{ + /// + /// Fetches data for the specified range asynchronously. + /// + /// + /// The range for which to fetch data. + /// + /// + /// A cancellation token to cancel the operation. + /// + /// + /// A task that represents the asynchronous fetch operation. + /// The task result contains an enumerable of data of type + /// for the specified range. + /// + Task> FetchAsync( + Range range, + CancellationToken cancellationToken + ); + + /// + /// Fetches data for multiple specified ranges asynchronously. + /// This method can be used for batch fetching to optimize data retrieval when multiple ranges are needed. + /// + /// + /// The ranges for which to fetch data. + /// + /// + /// A cancellation token to cancel the operation. + /// + /// + /// A task that represents the asynchronous fetch operation. + /// The task result contains an enumerable of + /// for the specified ranges. + /// + /// + /// Default Behavior: + /// + /// The default implementation fetches each range in parallel by calling + /// for each range. + /// This provides automatic parallelization without additional implementation effort. + /// + /// When to Override: + /// + /// Override this method if your data source supports true batch optimization, such as: + /// + /// + /// Single database query that can fetch multiple ranges at once + /// Batch API endpoints that accept multiple range parameters + /// Custom batching logic with size limits or throttling + /// + /// + async Task>> FetchAsync( + IEnumerable> ranges, + CancellationToken cancellationToken + ) + { + var tasks = ranges.Select(async range => + new RangeChunk( + range, + await FetchAsync(range, cancellationToken) + ) + ); + + return await Task.WhenAll(tasks); + } +} \ No newline at end of file diff --git a/src/SlidingWindowCache/Public/WindowCache.cs b/src/SlidingWindowCache/Public/WindowCache.cs new file mode 100644 index 0000000..6f0605e --- /dev/null +++ b/src/SlidingWindowCache/Public/WindowCache.cs @@ -0,0 +1,217 @@ +using Intervals.NET; +using Intervals.NET.Domain.Abstractions; +using SlidingWindowCache.Core.Planning; +using SlidingWindowCache.Core.Rebalance.Decision; +using SlidingWindowCache.Core.Rebalance.Execution; +using SlidingWindowCache.Core.Rebalance.Intent; +using SlidingWindowCache.Core.State; +using SlidingWindowCache.Core.UserPath; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Infrastructure.Storage; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Public; + +/// +/// Represents a sliding window cache that retrieves and caches data for specified ranges, +/// with automatic rebalancing based on access patterns. +/// +/// +/// The type representing the range boundaries. Must implement . +/// +/// +/// The type of data being cached. +/// +/// +/// The type representing the domain of the ranges. Must implement . +/// Supports both fixed-step (O(1)) and variable-step (O(N)) domains. While variable-step domains +/// have O(N) complexity for range calculations, this cost is negligible compared to data source I/O. +/// +/// +/// Domain Flexibility: +/// +/// This cache works with any implementation, whether fixed-step +/// or variable-step. The in-memory cost of O(N) step counting (microseconds) is orders of magnitude +/// smaller than typical data source operations (milliseconds to seconds via network/disk I/O). +/// +/// Examples: +/// +/// Fixed-step: DateTimeDayFixedStepDomain, IntegerFixedStepDomain (O(1) operations) +/// Variable-step: Business days, months, custom calendars (O(N) operations, still fast) +/// +/// +public interface IWindowCache + where TRange : IComparable + where TDomain : IRangeDomain +{ + /// + /// Retrieves data for the specified range, utilizing the sliding window cache mechanism. + /// + /// + /// The range for which to retrieve data. + /// + /// + /// A cancellation token to cancel the operation. + /// + /// + /// A task that represents the asynchronous operation. The task result contains a + /// of data for the specified range from the materialized cache. + /// + ValueTask> GetDataAsync( + Range requestedRange, + CancellationToken cancellationToken); +} + +/// +/// +/// Architecture: +/// +/// WindowCache acts as a Public Facade and Composition Root. +/// It wires together all internal actors but does not implement business logic itself. +/// All user requests are delegated to the internal actor. +/// +/// Internal Actors: +/// +/// UserRequestHandler - Fast Path Actor (User Thread) +/// RebalanceIntentManager - Temporal Authority (Background) +/// RebalanceDecisionEngine - Pure Decision Logic (Background) +/// RebalanceExecutor - Mutating Actor (Background) +/// +/// +public sealed class WindowCache + : IWindowCache + where TRange : IComparable + where TDomain : IRangeDomain +{ + // Internal actors + private readonly UserRequestHandler _userRequestHandler; + private readonly IntentController _intentController; + + /// + /// Initializes a new instance of the class. + /// + /// + /// The data source from which to fetch data. + /// + /// + /// The domain defining the range characteristics. + /// + /// + /// The configuration options for the window cache. + /// + /// + /// Optional diagnostics interface for logging and metrics. Can be null if diagnostics are not needed. + /// + /// + /// Thrown when an unknown read mode is specified in the options. + /// + public WindowCache( + IDataSource dataSource, + TDomain domain, + WindowCacheOptions options, + ICacheDiagnostics? cacheDiagnostics = null + ) + { + // Initialize diagnostics (use NoOpDiagnostics if null to avoid null checks in actors) + cacheDiagnostics ??= new NoOpDiagnostics(); + var cacheStorage = CreateCacheStorage(domain, options); + var state = new CacheState(cacheStorage, domain); + + // Initialize all internal actors following corrected execution context model + var rebalancePolicy = new ThresholdRebalancePolicy(options, domain); + var rangePlanner = new ProportionalRangePlanner(options, domain); + var cacheFetcher = new CacheDataExtensionService(dataSource, domain, cacheDiagnostics); + + var decisionEngine = new RebalanceDecisionEngine(rebalancePolicy, rangePlanner); + var executor = + new RebalanceExecutor(state, cacheFetcher, rebalancePolicy, cacheDiagnostics); + + // IntentController composes with Execution Scheduler to form the Rebalance Intent Manager actor + _intentController = new IntentController( + state, + decisionEngine, + executor, + options.DebounceDelay, + cacheDiagnostics + ); + + // Initialize the UserRequestHandler (Fast Path Actor) + _userRequestHandler = new UserRequestHandler( + state, + cacheFetcher, + _intentController, + dataSource, + cacheDiagnostics + ); + + return; + + // Factory method to create the appropriate cache storage based on the specified read mode in options + static ICacheStorage CreateCacheStorage( + TDomain fixedStepDomain, + WindowCacheOptions windowCacheOptions + ) => windowCacheOptions.ReadMode switch + { + UserCacheReadMode.Snapshot => new SnapshotReadStorage(fixedStepDomain), + UserCacheReadMode.CopyOnRead => new CopyOnReadStorage(fixedStepDomain), + _ => throw new ArgumentOutOfRangeException(nameof(windowCacheOptions.ReadMode), + windowCacheOptions.ReadMode, "Unknown read mode.") + }; + } + + /// + /// + /// This method acts as a thin delegation layer to the internal actor. + /// WindowCache itself implements no business logic - it is a pure facade. + /// + public ValueTask> GetDataAsync( + Range requestedRange, + CancellationToken cancellationToken) + { + // Pure facade: delegate to UserRequestHandler actor + return _userRequestHandler.HandleRequestAsync(requestedRange, cancellationToken); + } + + /// + /// Waits for any pending background rebalance operations to complete. + /// This is an infrastructure API, not part of the domain semantics. + /// + /// + /// Maximum time to wait for idle state. Defaults to 30 seconds. + /// Throws if background tasks do not stabilize within this period. + /// + /// + /// A Task that completes when all scheduled background rebalance operations have finished. + /// + /// + /// Infrastructure API: + /// + /// This method provides deterministic synchronization with background rebalance execution + /// for testing, graceful shutdown, health checks, and integration scenarios. It is NOT part + /// of the cache's domain semantics or normal usage patterns. + /// + /// Use Cases: + /// + /// Test stabilization: Ensure cache has converged before assertions + /// Graceful shutdown: Wait for background work before disposing resources + /// Health checks: Verify rebalance operations are completing successfully + /// Integration scenarios: Synchronize with background work completion + /// Diagnostic scenarios: Verify rebalance execution has finished + /// + /// Actor Responsibility Boundaries: + /// + /// This method does NOT alter actor responsibilities. It is a pure delegation facade: + /// + /// + /// UserRequestHandler remains the ONLY publisher of rebalance intents + /// IntentController remains the lifecycle authority for intent cancellation + /// RebalanceScheduler remains the authority for background Task execution + /// WindowCache remains a composition root with no business logic + /// + /// + /// This method exists solely to expose the idle synchronization mechanism through the public API + /// for infrastructure purposes, maintaining the existing architectural separation. + /// + /// + public Task WaitForIdleAsync(TimeSpan? timeout = null) => _intentController.WaitForIdleAsync(timeout); +} \ No newline at end of file diff --git a/src/SlidingWindowCache/SlidingWindowCache.csproj b/src/SlidingWindowCache/SlidingWindowCache.csproj new file mode 100644 index 0000000..45bf19b --- /dev/null +++ b/src/SlidingWindowCache/SlidingWindowCache.csproj @@ -0,0 +1,43 @@ + + + + net8.0 + enable + enable + + + SlidingWindowCache + 0.0.1 + blaze6950 + SlidingWindowCache + A read-only, range-based, sequential-optimized cache with background rebalancing and cancellation-aware prefetching. Designed for scenarios with predictable sequential data access patterns like time-series data, paginated datasets, and streaming content. + MIT + https://github.com/blaze6950/SlidingWindowCache + https://github.com/blaze6950/SlidingWindowCache + git + cache;sliding-window;range-based;async;prefetching;time-series;sequential-access;intervals;performance + README.md + Initial release with core sliding window cache functionality, background rebalancing, and WebAssembly support. + false + true + snupkg + true + true + + + + + + + + + + + + + + + + + + diff --git a/tests/SlidingWindowCache.Integration.Tests/CacheDataSourceInteractionTests.cs b/tests/SlidingWindowCache.Integration.Tests/CacheDataSourceInteractionTests.cs new file mode 100644 index 0000000..caa1442 --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/CacheDataSourceInteractionTests.cs @@ -0,0 +1,407 @@ +using Intervals.NET.Domain.Default.Numeric; +using Intervals.NET.Domain.Extensions.Fixed; +using SlidingWindowCache.Integration.Tests.TestInfrastructure; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Integration.Tests; + +/// +/// Tests validating the interaction contract between WindowCache and IDataSource. +/// Uses SpyDataSource to capture and verify requested ranges without testing internal logic. +/// +/// Goal: Verify integration assumptions, not DataSource implementation: +/// - Cache miss triggers exact requested range fetch +/// - Partial cache hit fetches only missing segments +/// - Rebalance triggers correct expansion ranges +/// - No redundant fetches occur +/// +public sealed class CacheDataSourceInteractionTests : IAsyncDisposable +{ + private readonly IntegerFixedStepDomain _domain; + private readonly SpyDataSource _dataSource; + private WindowCache? _cache; + private readonly EventCounterCacheDiagnostics _cacheDiagnostics; + + public CacheDataSourceInteractionTests() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SpyDataSource(); + _cacheDiagnostics = new EventCounterCacheDiagnostics(); + } + + /// + /// Ensures any background rebalance operations are completed before executing next test + /// + public async ValueTask DisposeAsync() + { + // Wait for any background rebalance from current test to complete + await _cache!.WaitForIdleAsync(); + _dataSource.Reset(); + } + + private WindowCache CreateCache(WindowCacheOptions? options = null) + { + _cache = new WindowCache( + _dataSource, + _domain, + options ?? new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2 + ), + _cacheDiagnostics + ); + return _cache; + } + + #region Cache Miss Scenarios + + [Fact] + public async Task CacheMiss_ColdStart_DataSourceReceivesExactRequestedRange() + { + // ARRANGE + var cache = CreateCache(); + var requestedRange = Intervals.NET.Factories.Range.Closed(100, 110); + + // ACT + var data = await cache.GetDataAsync(requestedRange, CancellationToken.None); + + // ASSERT - DataSource was called with the requested range + Assert.True(_dataSource.TotalFetchCount > 0, "DataSource should be called for cold start"); + + // ASSERT - Verify IDataSource covered the exact requested range + Assert.True(_dataSource.WasRangeCovered(100, 110), + "DataSource should be asked to fetch at least the requested range [100, 110]"); + + // Verify data is correct + var array = data.ToArray(); + Assert.Equal((int)requestedRange.Span(_domain), array.Length); + Assert.Equal(100, array[0]); + Assert.Equal(110, array[^1]); + } + + [Fact] + public async Task CacheMiss_NonOverlappingJump_DataSourceReceivesNewRange() + { + // ARRANGE + var cache = CreateCache(); + + // First request establishes cache + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await cache.WaitForIdleAsync(); + + _dataSource.Reset(); // Track only the second request + + // ACT - Jump to non-overlapping range + var newRange = Intervals.NET.Factories.Range.Closed(500, 510); + var data = await cache.GetDataAsync(newRange, CancellationToken.None); + + // ASSERT - DataSource was called for new range + Assert.True(_dataSource.TotalFetchCount > 0, "DataSource should be called for non-overlapping range"); + + // Verify correct data + var array = data.ToArray(); + Assert.Equal(11, array.Length); + Assert.Equal(500, array[0]); + Assert.Equal(510, array[^1]); + } + + #endregion + + #region Partial Cache Hit Scenarios + + [Fact] + public async Task PartialCacheHit_OverlappingRange_FetchesOnlyMissingSegments() + { + // ARRANGE + var cache = CreateCache(); + + // First request establishes cache [100, 110] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ACT - Request overlapping range [105, 120] + // Should fetch only missing portion [111, 120] + var overlappingRange = Intervals.NET.Factories.Range.Closed(105, 120); + var data = await cache.GetDataAsync(overlappingRange, CancellationToken.None); + + // ASSERT - Verify returned data is correct + var array = data.ToArray(); + Assert.Equal(16, array.Length); // [105, 120] = 16 elements + Assert.Equal(105, array[0]); + Assert.Equal(120, array[^1]); + + // DataSource may or may not be called depending on cache expansion + // We verify behavior is correct regardless + for (var i = 0; i < array.Length; i++) + { + Assert.Equal(105 + i, array[i]); + } + } + + [Fact] + public async Task PartialCacheHit_LeftExtension_DataCorrect() + { + // ARRANGE + var cache = CreateCache(); + + // Establish cache at [200, 210] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(200, 210), CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ACT - Extend to the left [190, 205] + var leftExtendRange = Intervals.NET.Factories.Range.Closed(190, 205); + var data = await cache.GetDataAsync(leftExtendRange, CancellationToken.None); + + // ASSERT - Verify data correctness + var array = data.ToArray(); + Assert.Equal(16, array.Length); + Assert.Equal(190, array[0]); + Assert.Equal(205, array[^1]); + } + + [Fact] + public async Task PartialCacheHit_RightExtension_DataCorrect() + { + // ARRANGE + var cache = CreateCache(); + + // Establish cache at [300, 310] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(300, 310), CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ACT - Extend to the right [305, 320] + var rightExtendRange = Intervals.NET.Factories.Range.Closed(305, 320); + var data = await cache.GetDataAsync(rightExtendRange, CancellationToken.None); + + // ASSERT - Verify data correctness + var array2 = data.ToArray(); + Assert.Equal(16, array2.Length); + Assert.Equal(305, array2[0]); + Assert.Equal(320, array2[^1]); + } + + #endregion + + #region Rebalance Expansion Tests + + [Fact] + public async Task Rebalance_WithExpansionCoefficients_ExpandsCacheCorrectly() + { + // ARRANGE - Cache with 2x expansion (leftSize=2.0, rightSize=2.0) + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 2.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.3, + debounceDelay: TimeSpan.FromMilliseconds(50) + )); + + // ACT - Request range [100, 110] (11 elements) + // Expected expansion: left by 22, right by 22 -> cache becomes [78, 132] + var requestedRange = Intervals.NET.Factories.Range.Closed(100, 110); + var data = await cache.GetDataAsync(requestedRange, CancellationToken.None); + + // Wait for rebalance to complete + await cache.WaitForIdleAsync(); + + // Make a request within expected expanded cache + _dataSource.Reset(); + var withinExpanded = Intervals.NET.Factories.Range.Closed(85, 95); + var data2 = await cache.GetDataAsync(withinExpanded, CancellationToken.None); + + // ASSERT - Verify data correctness + var array1 = data.ToArray(); + var array2 = data2.ToArray(); + Assert.Equal(11, array1.Length); + Assert.Equal(100, array1[0]); + Assert.Equal(11, array2.Length); + Assert.Equal(85, array2[0]); + } + + [Fact] + public async Task Rebalance_SequentialRequests_CacheAdaptsToPattern() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1.5, + rightCacheSize: 1.5, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2, + debounceDelay: TimeSpan.FromMilliseconds(50) + )); + + // ACT - Sequential access pattern moving right + var ranges = new[] + { + Intervals.NET.Factories.Range.Closed(100, 110), + Intervals.NET.Factories.Range.Closed(120, 130), + Intervals.NET.Factories.Range.Closed(140, 150) + }; + + foreach (var range in ranges) + { + var data = await cache.GetDataAsync(range, CancellationToken.None); + Assert.Equal((int)range.Span(_domain), data.Length); + await cache.WaitForIdleAsync(); + } + + // ASSERT - System handled sequential pattern without errors + // Each request returned correct data + Assert.True(true, "Sequential pattern handled successfully"); + } + + #endregion + + #region No Redundant Fetches + + [Fact] + public async Task NoRedundantFetches_RepeatedSameRange_UsesCache() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions(1, 1, UserCacheReadMode.Snapshot, 0.4, 0.4)); + var range = Intervals.NET.Factories.Range.Closed(100, 110); + + // ACT - First request + await cache.GetDataAsync(range, CancellationToken.None); + await cache.WaitForIdleAsync(); + + // Second identical request + var data2 = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT - Second request should not trigger additional fetch (served from cache) + // Note: May trigger rebalance fetch in background, but user data served from cache + var array = data2.ToArray(); + Assert.Equal(11, array.Length); + Assert.Equal(100, array[0]); + } + + [Fact] + public async Task NoRedundantFetches_SubsetOfCache_NoAdditionalFetch() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 2.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.3, + debounceDelay: TimeSpan.FromMilliseconds(50) + )); + + // ACT - Large initial request + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 200), CancellationToken.None); + await cache.WaitForIdleAsync(); + + var totalFetchesAfterExpansion = _dataSource.TotalFetchCount; + Assert.True(totalFetchesAfterExpansion > 0, "Initial request should trigger fetches"); + + _dataSource.Reset(); + + // Request subset that should be in expanded cache + var subset = Intervals.NET.Factories.Range.Closed(150, 160); + var data = await cache.GetDataAsync(subset, CancellationToken.None); + + // ASSERT - Data is correct + var array = data.ToArray(); + Assert.Equal(11, array.Length); + Assert.Equal(150, array[0]); + Assert.Equal(160, array[^1]); + + // ASSERT - Subset request should ideally hit cache without new fetch + // (Background rebalance may occur, but subset data should be cached) + Assert.True(true, $"Subset request completed with fetch count: {_dataSource.TotalFetchCount}"); + } + + #endregion + + #region DataSource Call Verification + + [Fact] + public async Task DataSourceCalls_SingleFetchMethod_CalledForSimpleRanges() + { + // ARRANGE + var cache = CreateCache(); + + // ACT + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + + // ASSERT - At least one fetch call made + Assert.True(_dataSource.TotalFetchCount >= 1, + $"Expected at least 1 fetch, but got {_dataSource.TotalFetchCount}"); + } + + [Fact] + public async Task DataSourceCalls_MultipleCacheMisses_EachTriggersFetch() + { + // ARRANGE + var cache = CreateCache(); + + // ACT - Three non-overlapping ranges (guaranteed cache misses) + var ranges = new[] + { + Intervals.NET.Factories.Range.Closed(100, 110), + Intervals.NET.Factories.Range.Closed(1000, 1010), + Intervals.NET.Factories.Range.Closed(10000, 10010) + }; + + foreach (var range in ranges) + { + _dataSource.Reset(); + _ = await cache.GetDataAsync(range, CancellationToken.None); + + // Each miss should trigger at least one fetch + Assert.True(_dataSource.TotalFetchCount >= 1, + $"Cache miss should trigger fetch for range {range}"); + } + + // ASSERT - All data correct + Assert.True(true, "All cache misses triggered DataSource calls"); + } + + #endregion + + #region Edge Cases + + [Fact] + public async Task EdgeCase_VerySmallRange_SingleElement_HandlesCorrectly() + { + // ARRANGE + var cache = CreateCache(); + + // ACT + var singleElementRange = Intervals.NET.Factories.Range.Closed(42, 42); + var data = await cache.GetDataAsync(singleElementRange, CancellationToken.None); + + // ASSERT + var array1 = data.ToArray(); + Assert.Single(array1); + Assert.Equal(42, array1[0]); + Assert.True(_dataSource.TotalFetchCount >= 1); + } + + [Fact] + public async Task EdgeCase_VeryLargeRange_HandlesWithoutError() + { + // ARRANGE + var cache = CreateCache(); + + // ACT - Large range (1000 elements) + var largeRange = Intervals.NET.Factories.Range.Closed(0, 999); + var data = await cache.GetDataAsync(largeRange, CancellationToken.None); + + // ASSERT + var array2 = data.ToArray(); + Assert.Equal(1000, array2.Length); + Assert.Equal(0, array2[0]); + Assert.Equal(999, array2[^1]); + } + + #endregion +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Integration.Tests/ConcurrencyStabilityTests.cs b/tests/SlidingWindowCache.Integration.Tests/ConcurrencyStabilityTests.cs new file mode 100644 index 0000000..4cb3564 --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/ConcurrencyStabilityTests.cs @@ -0,0 +1,442 @@ +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using SlidingWindowCache.Integration.Tests.TestInfrastructure; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Integration.Tests; + +/// +/// Concurrency and stress stability tests for WindowCache. +/// Validates system stability under concurrent load and high volume requests. +/// +/// Goal: Verify robustness under concurrent scenarios: +/// - No crashes or exceptions +/// - No deadlocks +/// - Valid data returned for all requests +/// - Avoids fragile timing assertions +/// +public sealed class ConcurrencyStabilityTests : IAsyncDisposable +{ + private readonly IntegerFixedStepDomain _domain; + private readonly SpyDataSource _dataSource; + private WindowCache? _cache; + private readonly EventCounterCacheDiagnostics _cacheDiagnostics; + + public ConcurrencyStabilityTests() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SpyDataSource(); + _cacheDiagnostics = new EventCounterCacheDiagnostics(); + } + + /// + /// Ensures any background rebalance operations are completed before executing next test + /// + public async ValueTask DisposeAsync() + { + // Wait for any background rebalance from current test to complete + await _cache!.WaitForIdleAsync(); + _dataSource.Reset(); + } + + private WindowCache CreateCache(WindowCacheOptions? options = null) + { + return _cache = new WindowCache( + _dataSource, + _domain, + options ?? new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2, + debounceDelay: TimeSpan.FromMilliseconds(20) + ), + _cacheDiagnostics + ); + } + + #region Basic Concurrency Tests + + [Fact] + public async Task Concurrent_10SimultaneousRequests_AllSucceed() + { + // ARRANGE + var cache = CreateCache(); + const int concurrentRequests = 10; + + // ACT - Execute requests concurrently + var tasks = new List>>(); + for (var i = 0; i < concurrentRequests; i++) + { + var start = i * 100; + var range = Intervals.NET.Factories.Range.Closed(start, start + 20); + tasks.Add(cache.GetDataAsync(range, CancellationToken.None).AsTask()); + } + + var results = await Task.WhenAll(tasks); + + // ASSERT - All requests completed successfully + Assert.Equal(concurrentRequests, results.Length); + + foreach (var t in results) + { + Assert.Equal(21, t.Length); // Each range has 21 elements + } + + // ASSERT - IDataSource was called and handled concurrent requests + Assert.True(_dataSource.TotalFetchCount > 0, "IDataSource should handle concurrent requests"); + + // Verify all requested ranges are valid + var allRanges = _dataSource.GetAllRequestedRanges(); + Assert.All(allRanges, + range => { Assert.True((int)range.Start <= (int)range.End, "All concurrent ranges should be valid"); }); + } + + [Fact] + public async Task Concurrent_SameRangeMultipleTimes_NoDeadlock() + { + // ARRANGE + var cache = CreateCache(); + const int concurrentRequests = 20; + var range = Intervals.NET.Factories.Range.Closed(100, 120); + + // ACT - Many concurrent requests for same range + var tasks = Enumerable.Range(0, concurrentRequests) + .Select(_ => cache.GetDataAsync(range, CancellationToken.None).AsTask()) + .ToList(); + + var results = await Task.WhenAll(tasks); + + // ASSERT - All completed, no deadlock + Assert.Equal(concurrentRequests, results.Length); + + foreach (var result in results) + { + var array = result.ToArray(); + Assert.Equal(21, array.Length); + Assert.Equal(100, array[0]); + Assert.Equal(120, array[^1]); + } + } + + #endregion + + #region Overlapping Range Concurrency + + [Fact] + public async Task Concurrent_OverlappingRanges_AllDataValid() + { + // ARRANGE + var cache = CreateCache(); + const int concurrentRequests = 15; + + // ACT - Overlapping ranges around center point + var tasks = new List>>(); + for (var i = 0; i < concurrentRequests; i++) + { + var offset = i * 5; + var range = Intervals.NET.Factories.Range.Closed(100 + offset, 150 + offset); + tasks.Add(cache.GetDataAsync(range, CancellationToken.None).AsTask()); + } + + var results = await Task.WhenAll(tasks); + + // ASSERT - Verify each result + for (var i = 0; i < results.Length; i++) + { + var offset = i * 5; + var expected = 51; // [100+offset, 150+offset] = 51 elements + var array = results[i].ToArray(); + Assert.Equal(expected, array.Length); + Assert.Equal(100 + offset, array[0]); + } + } + + #endregion + + #region High Volume Stress Tests + + [Fact] + public async Task HighVolume_100SequentialRequests_NoErrors() + { + // ARRANGE + var cache = CreateCache(); + const int requestCount = 100; + var exceptions = new List(); + + // ACT + for (var i = 0; i < requestCount; i++) + { + try + { + var start = i * 10; + var range = Intervals.NET.Factories.Range.Closed(start, start + 15); + var data = await cache.GetDataAsync(range, CancellationToken.None); + + Assert.Equal(16, data.Length); + } + catch (Exception ex) + { + exceptions.Add(ex); + } + } + + // ASSERT + Assert.Empty(exceptions); + } + + [Fact] + public async Task HighVolume_50ConcurrentBursts_SystemStable() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1.5, + rightCacheSize: 1.5, + readMode: UserCacheReadMode.CopyOnRead, + leftThreshold: 0.25, + rightThreshold: 0.25, + debounceDelay: TimeSpan.FromMilliseconds(10) + )); + + const int burstSize = 50; + + // ACT - Launch many concurrent requests + var tasks = new List>>(); + for (var i = 0; i < burstSize; i++) + { + var start = (i % 10) * 50; // Create some overlap + var range = Intervals.NET.Factories.Range.Closed(start, start + 25); + tasks.Add(cache.GetDataAsync(range, CancellationToken.None).AsTask()); + } + + var results = await Task.WhenAll(tasks); + + // ASSERT - All completed successfully + Assert.Equal(burstSize, results.Length); + Assert.All(results, r => Assert.Equal(26, r.Length)); + } + + #endregion + + #region Mixed Concurrent Operations + + [Fact] + public async Task MixedConcurrent_RandomAndSequential_NoConflicts() + { + // ARRANGE + var cache = CreateCache(); + var random = new Random(42); + const int totalTasks = 40; + + // ACT - Mix of random and sequential requests + var tasks = new List>>(); + + for (var i = 0; i < totalTasks; i++) + { + Range range; + + if (i % 2 == 0) + { + // Sequential + var start = i * 20; + range = Intervals.NET.Factories.Range.Closed(start, start + 30); + } + else + { + // Random + var start = random.Next(0, 1000); + range = Intervals.NET.Factories.Range.Closed(start, start + 20); + } + + tasks.Add(cache.GetDataAsync(range, CancellationToken.None).AsTask()); + } + + var results = await Task.WhenAll(tasks); + + // ASSERT + Assert.Equal(totalTasks, results.Length); + Assert.All(results, r => Assert.True(r.Length > 0)); + } + + #endregion + + #region Cancellation Under Load + + [Fact] + public async Task CancellationUnderLoad_SystemStableWithCancellations() + { + // ARRANGE + var cache = CreateCache(); + const int requestCount = 30; + var ctsList = new List(); + + // ACT - Launch requests with delayed cancellations + var tasks = new List>(); + + for (var i = 0; i < requestCount; i++) + { + var cts = new CancellationTokenSource(); + ctsList.Add(cts); + + var start = i * 10; + var range = Intervals.NET.Factories.Range.Closed(start, start + 15); + + tasks.Add(Task.Run(async () => + { + try + { + await cache.GetDataAsync(range, cts.Token); + return true; // Success + } + catch (OperationCanceledException) + { + return false; // Cancelled + } + }, CancellationToken.None)); + + // Cancel some requests with delay + if (i % 5 == 0) + { + _ = Task.Run(async () => + { + await Task.Delay(5, CancellationToken.None); + await cts.CancelAsync(); + }, CancellationToken.None); + } + } + + var results = await Task.WhenAll(tasks); + + // ASSERT - System handled mix gracefully (some succeeded, some may be cancelled) + var successCount = results.Count(r => r); + Assert.True(successCount > 0, "At least some requests should succeed"); + + // Cleanup + foreach (var cts in ctsList) + { + cts.Dispose(); + } + } + + #endregion + + #region Rapid Fire Tests + + [Fact] + public async Task RapidFire_100RequestsMinimalDelay_NoDeadlock() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 2.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.3, + debounceDelay: TimeSpan.FromMilliseconds(5) + )); + + const int requestCount = 100; + + // ACT - Rapid sequential requests + for (var i = 0; i < requestCount; i++) + { + var start = (i % 20) * 10; // Create overlap pattern + var range = Intervals.NET.Factories.Range.Closed(start, start + 20); + var data = await cache.GetDataAsync(range, CancellationToken.None); + + Assert.Equal(21, data.Length); + } + + // ASSERT - Completed without deadlock + Assert.True(true); + } + + #endregion + + #region Data Integrity Under Concurrency + + [Fact] + public async Task DataIntegrity_ConcurrentReads_AllDataCorrect() + { + // ARRANGE + var cache = CreateCache(); + const int concurrentReaders = 25; + var baseRange = Intervals.NET.Factories.Range.Closed(500, 600); + + // Warm up cache + await cache.GetDataAsync(baseRange, CancellationToken.None); + await cache.WaitForIdleAsync(); + + var initialFetchCount = _dataSource.TotalFetchCount; + + // ACT - Many concurrent reads of overlapping ranges + var tasks = new List>(); + + for (var i = 0; i < concurrentReaders; i++) + { + var offset = i * 4; + var expectedFirst = 500 + offset; + tasks.Add(Task.Run(async () => + { + var range = Intervals.NET.Factories.Range.Closed(500 + offset, 550 + offset); + var data = await cache.GetDataAsync(range, CancellationToken.None); + var array = data.ToArray(); + return (array.Length, array[0], expectedFirst); + })); + } + + var results = await Task.WhenAll(tasks); + + // ASSERT - No data corruption + foreach (var (length, firstValue, expectedFirst) in results) + { + Assert.Equal(51, length); + Assert.Equal(expectedFirst, firstValue); + } + + // ASSERT - Concurrent reads should mostly hit cache after warmup + var finalFetchCount = _dataSource.TotalFetchCount; + Assert.True(finalFetchCount >= initialFetchCount, "May have additional fetches for range extensions"); + + // Verify no malformed ranges during concurrent access + var allRanges = _dataSource.GetAllRequestedRanges(); + Assert.All(allRanges, + range => + { + Assert.True((int)range.Start <= (int)range.End, "No data races should produce invalid ranges"); + }); + } + + #endregion + + #region Timeout Protection + + [Fact] + public async Task TimeoutProtection_LongRunningTest_CompletesWithinReasonableTime() + { + // ARRANGE + var cache = CreateCache(); + const int requestCount = 50; + var timeout = TimeSpan.FromSeconds(30); + + // ACT + using var cts = new CancellationTokenSource(timeout); + var tasks = new List(); + + for (var i = 0; i < requestCount; i++) + { + var start = i * 15; + var range = Intervals.NET.Factories.Range.Closed(start, start + 25); + tasks.Add(cache.GetDataAsync(range, cts.Token).AsTask()); + } + + // ASSERT - Completes within timeout + await Task.WhenAll(tasks); + Assert.False(cts.Token.IsCancellationRequested, "Should complete before timeout"); + } + + #endregion +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Integration.Tests/DataSourceRangePropagationTests.cs b/tests/SlidingWindowCache.Integration.Tests/DataSourceRangePropagationTests.cs new file mode 100644 index 0000000..2fea1bb --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/DataSourceRangePropagationTests.cs @@ -0,0 +1,469 @@ +using Intervals.NET.Domain.Default.Numeric; +using SlidingWindowCache.Integration.Tests.TestInfrastructure; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Integration.Tests; + +/// +/// Tests that validate the EXACT ranges propagated to IDataSource in different cache scenarios. +/// These tests provide precise behavioral contracts ("alibi") proving the cache requests +/// correct ranges from the data source in every state transition. +/// +/// Scenarios covered: +/// - User Path: Cache miss (cold start) +/// - User Path: Cache hit (full cache coverage) +/// - User Path: Partial cache hit (left extension, right extension) +/// - Rebalance: After cold start +/// - Rebalance: With right-side expansion +/// - Rebalance: With left-side expansion +/// +public sealed class DataSourceRangePropagationTests : IAsyncDisposable +{ + private readonly IntegerFixedStepDomain _domain; + private readonly SpyDataSource _dataSource; + private WindowCache? _cache; + private EventCounterCacheDiagnostics _cacheDiagnostics; + + public DataSourceRangePropagationTests() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SpyDataSource(); + } + + public async ValueTask DisposeAsync() + { + await _cache!.WaitForIdleAsync(); + _dataSource.Reset(); + } + + private WindowCache CreateCache(WindowCacheOptions? options = null) + { + _cacheDiagnostics = new EventCounterCacheDiagnostics(); + _cache = new WindowCache( + _dataSource, + _domain, + options ?? new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2, + debounceDelay: TimeSpan.FromSeconds(1) + ), + _cacheDiagnostics + ); + return _cache; + } + + #region Cache Miss (Cold Start) + + [Fact] + public async Task CacheMiss_ColdStart_PropagatesExactUserRange() + { + // ARRANGE + var cache = CreateCache(); + var userRange = Intervals.NET.Factories.Range.Closed(100, 110); + + // ACT + var data = await cache.GetDataAsync(userRange, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(11, data.Length); + Assert.Equal(100, data.Span[0]); + Assert.Equal(110, data.Span[^1]); + + // ASSERT - IDataSource received exact user range on cold start + var requestedRanges = _dataSource.GetAllRequestedRanges(); + Assert.Single(requestedRanges); + + var fetchedRange = requestedRanges.First(); + Assert.Equal(userRange, fetchedRange); // Exact match for cold start + } + + [Fact] + public async Task CacheMiss_ColdStart_LargeRange_PropagatesExactly() + { + // ARRANGE + var cache = CreateCache(); + var userRange = Intervals.NET.Factories.Range.Closed(0, 999); + + // ACT + var data = await cache.GetDataAsync(userRange, CancellationToken.None); + + // ASSERT + Assert.Equal(1000, data.Length); + + // ASSERT - IDataSource received exact large range + var requestedRanges = _dataSource.GetAllRequestedRanges(); + var fetchedRange = requestedRanges.SingleOrDefault(); + + Assert.NotNull(requestedRanges); + Assert.Equal(userRange, fetchedRange); // Exact match for large range + } + + #endregion + + #region Cache Hit (Full Coverage) + + [Fact] + public async Task CacheHit_FullCoverage_NoAdditionalFetch() + { + // ARRANGE - Cache with large expansion to ensure second request is fully covered + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 3.0, + rightCacheSize: 3.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.3 + )); + + // First request: [100, 120] will expand to approximately [37, 183] with 3x coefficient + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 120), CancellationToken.None); + await _cache!.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Request subset that should be fully cached: [110, 115] + var subsetRange = Intervals.NET.Factories.Range.Closed(110, 115); + var data = await cache.GetDataAsync(subsetRange, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(6, data.Length); + Assert.Equal(110, data.Span[0]); + + // ASSERT - No additional fetch should occur (cache hit) + var newFetches = _dataSource.GetAllRequestedRanges(); + Assert.Empty(newFetches); // Perfect cache hit! + } + + #endregion + + #region Partial Cache Hit - Right Extension + + [Fact] + public async Task PartialCacheHit_RightExtension_FetchesOnlyMissingSegment() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1, + rightCacheSize: 1, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0, + rightThreshold: 0 + )); + + // First request establishes cache [200, 210] - 11 items, cache after rebalance [189, 221] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(200, 210), CancellationToken.None); + await _cache!.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Extend to right [220, 230] - overlaps existing [189, 221] + var rightExtension = Intervals.NET.Factories.Range.Closed(220, 230); + var data = await cache.GetDataAsync(rightExtension, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(11, data.Length); + Assert.Equal(220, data.Span[0]); + Assert.Equal(230, data.Span[^1]); + + // ASSERT - IDataSource should fetch only missing right segment (221, 230] + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.OpenClosed(221, 230)); + } + + #endregion + + #region Partial Cache Hit - Left Extension + + [Fact] + public async Task PartialCacheHit_LeftExtension_FetchesOnlyMissingSegment() + { + // ARRANGE - Cache WITHOUT expansion + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1, + rightCacheSize: 1, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0, + rightThreshold: 0 + )); + + // First request establishes cache [300, 310] - 11 items, cache after rebalance [289, 321] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(300, 310), CancellationToken.None); + await _cache!.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Extend to left [280, 290] - overlaps existing [289, 321] + var leftExtension = Intervals.NET.Factories.Range.Closed(280, 290); + var data = await cache.GetDataAsync(leftExtension, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(11, data.Length); + Assert.Equal(280, data.Span[0]); + Assert.Equal(290, data.Span[^1]); + + // ASSERT - IDataSource should fetch only missing left segment [280, 289) + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.ClosedOpen(280, 289)); + } + + #endregion + + #region Rebalance After Cold Start + + [Fact] + public async Task Rebalance_ColdStart_ExpandsSymmetrically() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1, + rightCacheSize: 1, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0, + rightThreshold: 0 + )); + + // ACT - Request [100, 110] - 11 items, cache after rebalance [89, 121] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ASSERT - Should fetch initial user range and rebalance expansions + var allRanges = _dataSource.GetAllRequestedRanges(); + Assert.Equal(3, allRanges.Count); // Initial fetch + 2 expansions + + // First fetch should be the user range + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.Closed(100, 110)); + + // Rebalance should expand symmetrically + // Left expansion: 11 * 1 = 11, so [89, 100) + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.ClosedOpen(89, 100)); + + // Right expansion: 11 * 2.0 = 22, so (110, 121] + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.OpenClosed(110, 121)); + } + + #endregion + + #region Rebalance with Right-Side Expansion + + [Fact] + public async Task Rebalance_RightMovement_ExpandsRightSide() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1, + rightCacheSize: 1, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0, + rightThreshold: 0 + )); + + // Establish initial cache at [100, 110] - 11 items, cache after rebalance [89, 121] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await cache.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Move right to [120, 130] - 11 items, overlaps existing [89, 121] + var rightRange = Intervals.NET.Factories.Range.Closed(120, 130); + await cache.GetDataAsync(rightRange, CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ASSERT + // First fetch should be the missing segment + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.OpenClosed(121, 130)); + + // Rebalance may trigger right expansion + // Expected right expansion: 11 * 1 = 11, so (130, 141] + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.OpenClosed(130, 141)); + } + + #endregion + + #region Rebalance with Left-Side Expansion + + [Fact] + public async Task Rebalance_LeftMovement_ExpandsLeftSide() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1, + rightCacheSize: 1, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0, + rightThreshold: 0 + )); + + // Establish initial cache at [200, 210] - 11 items, cache after rebalance [189, 221] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(200, 210), CancellationToken.None); + await cache.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Move left to [180, 190] - 11 items, overlaps existing [189, 221] + var leftRange = Intervals.NET.Factories.Range.Closed(180, 190); + await cache.GetDataAsync(leftRange, CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ASSERT - Should fetch the new range + var requestedRanges = _dataSource.GetAllRequestedRanges(); + Assert.NotEmpty(requestedRanges); + + // First fetch should be the missing segment + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.ClosedOpen(180, 189)); + + // Rebalance may trigger left expansion + // Expected left expansion: 11 * 1 = 11, so [169, 180) + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.ClosedOpen(169, 180)); + } + + #endregion + + #region Partial Overlap Scenarios + + [Fact] + public async Task PartialOverlap_BothSides_FetchesBothMissingSegments() + { + // ARRANGE - No expansion for predictable behavior + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 1, + rightCacheSize: 1, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0, + rightThreshold: 0 + )); + + // Establish cache [100, 110] - 11 items, cache after rebalance [89, 121] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await _cache!.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Request [80, 130] which extends both left and right + var extendedRange = Intervals.NET.Factories.Range.Closed(80, 130); + var data = await cache.GetDataAsync(extendedRange, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(51, data.Length); + Assert.Equal(80, data.Span[0]); + Assert.Equal(130, data.Span[^1]); + + // ASSERT - Should fetch both missing segments + // Left segment [80, 89) and right segment (121, 130] + // May be fetched as 2 separate ranges or 1 consolidated range + var requestedRanges = _dataSource.GetAllRequestedRanges(); + Assert.Equal(2, requestedRanges.Count); // Expecting 2 separate fetches for left and right missing segments + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.ClosedOpen(80, 89)); + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.OpenClosed(121, 130)); + } + + #endregion + + #region Non-Overlapping Jump + + [Fact] + public async Task NonOverlappingJump_FetchesEntireNewRange() + { + // ARRANGE + var cache = CreateCache(); + + // Establish cache at [100, 110] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await _cache!.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Jump to non-overlapping [500, 510] + var jumpRange = Intervals.NET.Factories.Range.Closed(500, 510); + var data = await cache.GetDataAsync(jumpRange, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(11, data.Length); + Assert.Equal(500, data.Span[0]); + Assert.Equal(510, data.Span[^1]); + + // ASSERT - Should fetch entire new range + _dataSource.AssertRangeRequested(Intervals.NET.Factories.Range.Closed(500, 510)); + } + + #endregion + + #region Edge Case: Adjacent Ranges + + [Fact] + public async Task AdjacentRanges_RightAdjacent_FetchesExactNewSegment() + { + // ARRANGE - No expansion + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 0.0, + rightCacheSize: 0.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.0, + rightThreshold: 0.0, + debounceDelay: TimeSpan.FromMilliseconds(50) + )); + + // Establish cache [100, 110] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await _cache!.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Request adjacent right range [111, 120] + var adjacentRange = Intervals.NET.Factories.Range.Closed(111, 120); + var data = await cache.GetDataAsync(adjacentRange, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(10, data.Length); + Assert.Equal(111, data.Span[0]); + Assert.Equal(120, data.Span[^1]); + + // ASSERT - Should fetch only the new adjacent segment + var requestedRanges = _dataSource.GetAllRequestedRanges(); + Assert.Single(requestedRanges); + + var fetchedRange = requestedRanges.First(); + Assert.Equal(111, (int)fetchedRange.Start); + Assert.Equal(120, (int)fetchedRange.End); + } + + [Fact] + public async Task AdjacentRanges_LeftAdjacent_FetchesExactNewSegment() + { + // ARRANGE - No expansion + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 0.0, + rightCacheSize: 0.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.0, + rightThreshold: 0.0, + debounceDelay: TimeSpan.FromMilliseconds(50) + )); + + // Establish cache [100, 110] + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await _cache!.WaitForIdleAsync(); + + _dataSource.Reset(); + + // ACT - Request adjacent left range [90, 99] + var adjacentRange = Intervals.NET.Factories.Range.Closed(90, 99); + var data = await cache.GetDataAsync(adjacentRange, CancellationToken.None); + + // ASSERT - Data is correct + Assert.Equal(10, data.Length); + Assert.Equal(90, data.Span[0]); + Assert.Equal(99, data.Span[^1]); + + // ASSERT - Should fetch only the new adjacent segment + var requestedRanges = _dataSource.GetAllRequestedRanges(); + Assert.Single(requestedRanges); + + var fetchedRange = requestedRanges.First(); + Assert.Equal(90, (int)fetchedRange.Start); + Assert.Equal(99, (int)fetchedRange.End); + } + + #endregion +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Integration.Tests/RandomRangeRobustnessTests.cs b/tests/SlidingWindowCache.Integration.Tests/RandomRangeRobustnessTests.cs new file mode 100644 index 0000000..87f008a --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/RandomRangeRobustnessTests.cs @@ -0,0 +1,225 @@ +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using Intervals.NET.Domain.Extensions.Fixed; +using SlidingWindowCache.Integration.Tests.TestInfrastructure; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Integration.Tests; + +/// +/// Property-based robustness tests using randomized range requests. +/// Detects edge cases and invariant violations through many iterations. +/// Uses deterministic seed for reproducibility. +/// +public sealed class RandomRangeRobustnessTests : IAsyncDisposable +{ + private readonly IntegerFixedStepDomain _domain; + private readonly SpyDataSource _dataSource; + private readonly Random _random; + private WindowCache? _cache; + private EventCounterCacheDiagnostics _cacheDiagnostics; + + private const int RandomSeed = 42; + private const int MinRangeStart = -10000; + private const int MaxRangeStart = 10000; + private const int MinRangeLength = 1; + private const int MaxRangeLength = 100; + + public RandomRangeRobustnessTests() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SpyDataSource(); + _random = new Random(RandomSeed); + } + + /// + /// Ensures any background rebalance operations are completed before executing next test + /// + public async ValueTask DisposeAsync() + { + // Wait for any background rebalance from current test to complete + await _cache!.WaitForIdleAsync(); + _dataSource.Reset(); + } + + private WindowCache CreateCache(WindowCacheOptions? options = null) + { + _cacheDiagnostics = new EventCounterCacheDiagnostics(); + return _cache = new WindowCache( + _dataSource, + _domain, + options ?? new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2, + debounceDelay: TimeSpan.FromMilliseconds(10) + ), + _cacheDiagnostics + ); + } + + private Range GenerateRandomRange() + { + var start = _random.Next(MinRangeStart, MaxRangeStart); + var length = _random.Next(MinRangeLength, MaxRangeLength); + var end = start + length - 1; + return Intervals.NET.Factories.Range.Closed(start, end); + } + + [Fact] + public async Task RandomRanges_200Iterations_NoExceptions() + { + var cache = CreateCache(); + const int iterations = 200; + + for (var i = 0; i < iterations; i++) + { + var range = GenerateRandomRange(); + var data = await cache.GetDataAsync(range, CancellationToken.None); + Assert.Equal((int)range.Span(_domain), data.Length); + } + + // ASSERT - Verify IDataSource was called and no malformed ranges requested + Assert.True(_dataSource.TotalFetchCount > 0, "IDataSource should be called during random iterations"); + + // Verify all requested ranges are valid + var allRanges = _dataSource.GetAllRequestedRanges(); + Assert.All(allRanges, range => + { + var start = (int)range.Start; + var end = (int)range.End; + Assert.True(start <= end, $"Invalid range: start ({start}) > end ({end})"); + }); + } + + [Fact] + public async Task RandomRanges_DataContentAlwaysValid() + { + var cache = CreateCache(); + const int iterations = 150; + + for (var i = 0; i < iterations; i++) + { + var range = GenerateRandomRange(); + var data = await cache.GetDataAsync(range, CancellationToken.None); + + var start = (int)range.Start; + var array = data.ToArray(); // Convert to array to avoid ref struct in async + + for (var j = 0; j < array.Length; j++) + { + Assert.Equal(start + j, array[j]); + } + } + } + + [Fact] + public async Task RandomOverlappingRanges_NoExceptions() + { + var cache = CreateCache(); + const int iterations = 100; + + var baseStart = _random.Next(1000, 2000); + var baseRange = Intervals.NET.Factories.Range.Closed(baseStart, baseStart + 50); + await cache.GetDataAsync(baseRange, CancellationToken.None); + + for (var i = 0; i < iterations; i++) + { + var overlapStart = baseStart + _random.Next(-25, 25); + var overlapEnd = overlapStart + _random.Next(10, 40); + var range = Intervals.NET.Factories.Range.Closed(overlapStart, overlapEnd); + + var data = await cache.GetDataAsync(range, CancellationToken.None); + Assert.Equal((int)range.Span(_domain), data.Length); + } + } + + [Fact] + public async Task RandomAccessSequence_ForwardBackward_StableOperation() + { + var cache = CreateCache(); + const int iterations = 150; + var currentPosition = 5000; + + for (var i = 0; i < iterations; i++) + { + var direction = _random.Next(0, 2) == 0 ? -1 : 1; + var step = _random.Next(5, 20); + currentPosition += direction * step; + + var rangeLength = _random.Next(10, 30); + var range = Intervals.NET.Factories.Range.Closed( + currentPosition, + currentPosition + rangeLength - 1 + ); + + var data = await cache.GetDataAsync(range, CancellationToken.None); + var array = data.ToArray(); + Assert.Equal(rangeLength, array.Length); + Assert.Equal(currentPosition, array[0]); + } + } + + [Fact] + public async Task StressCombination_MixedPatterns_500Iterations() + { + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 2.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.CopyOnRead, + leftThreshold: 0.25, + rightThreshold: 0.25, + debounceDelay: TimeSpan.FromMilliseconds(5) + )); + + const int iterations = 500; + + for (var i = 0; i < iterations; i++) + { + Range range; + var pattern = _random.Next(0, 10); + + if (pattern < 5) + { + range = GenerateRandomRange(); + } + else if (pattern < 8) + { + var start = i * 10; + range = Intervals.NET.Factories.Range.Closed(start, start + 20); + } + else + { + var start = (i - 1) * 10 + 5; + range = Intervals.NET.Factories.Range.Closed(start, start + 25); + } + + var data = await cache.GetDataAsync(range, CancellationToken.None); + Assert.Equal((int)range.Span(_domain), data.Length); + } + + // ASSERT - Comprehensive validation of IDataSource interactions + var totalFetches = _dataSource.TotalFetchCount; + Assert.True(totalFetches > 0, "IDataSource should be called during stress test"); + Assert.True(totalFetches < iterations * 3, + $"Fetch count ({totalFetches}) should be reasonable for {iterations} mixed-pattern iterations"); + + // Verify all ranges requested are valid + var allRanges = _dataSource.GetAllRequestedRanges(); + Assert.NotEmpty(allRanges); + Assert.All(allRanges, r => + { + var start = (int)r.Start; + var end = (int)r.End; + Assert.True(start <= end, $"Invalid range detected: [{start}, {end}]"); + }); + + // Verify no excessive redundant fetches + var uniqueRanges = _dataSource.GetUniqueRequestedRanges(); + Assert.True(uniqueRanges.Count > 0, "Should have requested some unique ranges"); + } +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Integration.Tests/RangeSemanticsContractTests.cs b/tests/SlidingWindowCache.Integration.Tests/RangeSemanticsContractTests.cs new file mode 100644 index 0000000..7489127 --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/RangeSemanticsContractTests.cs @@ -0,0 +1,319 @@ +using Intervals.NET.Domain.Default.Numeric; +using Intervals.NET.Domain.Extensions.Fixed; +using SlidingWindowCache.Integration.Tests.TestInfrastructure; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Integration.Tests; + +/// +/// Tests that validate SlidingWindowCache assumptions about range semantics and behavior. +/// These tests focus on observable contract validation rather than internal implementation. +/// +/// Goal: Verify that range operations behave as expected regarding: +/// - Inclusivity and boundary correctness +/// - Returned data length matching requested range span +/// - Behavior with infinite boundaries +/// - Span consistency after expansions +/// +public sealed class RangeSemanticsContractTests : IAsyncDisposable +{ + private readonly IntegerFixedStepDomain _domain; + private readonly SpyDataSource _dataSource; + private WindowCache? _cache; + private EventCounterCacheDiagnostics _cacheDiagnostics; + + public RangeSemanticsContractTests() + { + _domain = new IntegerFixedStepDomain(); + _dataSource = new SpyDataSource(); + } + + /// + /// Ensures any background rebalance operations are completed before executing next test + /// + public async ValueTask DisposeAsync() + { + // Wait for any background rebalance from current test to complete + await _cache!.WaitForIdleAsync(); + _dataSource.Reset(); + } + + private WindowCache CreateCache(WindowCacheOptions? options = null) + { + _cacheDiagnostics = new EventCounterCacheDiagnostics(); + _cache = new WindowCache( + _dataSource, + _domain, + options ?? new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: 0.2, + debounceDelay: TimeSpan.FromMilliseconds(50) + ), + _cacheDiagnostics + ); + return _cache; + } + + #region Finite Range Tests + + [Fact] + public async Task FiniteRange_ClosedBoundaries_ReturnsCorrectLength() + { + // ARRANGE + var cache = CreateCache(); + var range = Intervals.NET.Factories.Range.Closed(100, 110); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT - Validate memory length matches range span + var expectedLength = (int)range.Span(_domain); + Assert.Equal(expectedLength, data.Length); + Assert.Equal(11, data.Length); // [100, 110] inclusive = 11 elements + + // ASSERT - Validate IDataSource was called with correct range + Assert.True(_dataSource.TotalFetchCount > 0, "DataSource should be called for cold start"); + Assert.True(_dataSource.WasRangeCovered(100, 110), "DataSource should cover requested range [100, 110]"); + } + + [Fact] + public async Task FiniteRange_BoundaryAlignment_ReturnsCorrectValues() + { + // ARRANGE + var cache = CreateCache(); + var range = Intervals.NET.Factories.Range.Closed(50, 55); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT - Validate boundary values are correct + var array = data.ToArray(); + Assert.Equal(50, array[0]); // First element matches start + Assert.Equal(55, array[^1]); // Last element matches end + Assert.True(array.SequenceEqual(new[] { 50, 51, 52, 53, 54, 55 })); + } + + [Fact] + public async Task FiniteRange_MultipleRequests_ConsistentLengths() + { + // ARRANGE + var cache = CreateCache(); + var ranges = new[] + { + Intervals.NET.Factories.Range.Closed(10, 20), // 11 elements + Intervals.NET.Factories.Range.Closed(100, 199), // 100 elements + Intervals.NET.Factories.Range.Closed(500, 501) // 2 elements + }; + + // ACT & ASSERT + foreach (var range in ranges) + { + var data = await cache.GetDataAsync(range, CancellationToken.None); + var expectedLength = (int)range.Span(_domain); + Assert.Equal(expectedLength, data.Length); + } + } + + [Fact] + public async Task FiniteRange_SingleElementRange_ReturnsOneElement() + { + // ARRANGE + var cache = CreateCache(); + var range = Intervals.NET.Factories.Range.Closed(42, 42); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT + var array = data.ToArray(); + Assert.Single(array); + Assert.Equal(42, array[0]); + } + + [Fact] + public async Task FiniteRange_DataContentMatchesRange_SequentialValues() + { + // ARRANGE + var cache = CreateCache(); + var range = Intervals.NET.Factories.Range.Closed(1000, 1010); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT - Verify sequential data from start to end + var array = data.ToArray(); + for (var i = 0; i < array.Length; i++) + { + Assert.Equal(1000 + i, array[i]); + } + } + + #endregion + + #region Infinite Boundary Tests + + [Fact] + public async Task InfiniteBoundary_LeftInfinite_CacheHandlesGracefully() + { + // ARRANGE + var cache = CreateCache(); + + // Note: IntegerFixedStepDomain uses int.MinValue for negative infinity + // We test behavior with very large ranges but finite boundaries + var range = Intervals.NET.Factories.Range.Closed(int.MinValue + 1000, int.MinValue + 1100); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT - No exceptions, correct length + var expectedLength = (int)range.Span(_domain); + Assert.Equal(expectedLength, data.Length); + } + + [Fact] + public async Task InfiniteBoundary_RightInfinite_CacheHandlesGracefully() + { + // ARRANGE + var cache = CreateCache(); + + // Note: IntegerFixedStepDomain uses int.MaxValue for positive infinity + var range = Intervals.NET.Factories.Range.Closed(int.MaxValue - 1100, int.MaxValue - 1000); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT - No exceptions, correct length + var expectedLength = (int)range.Span(_domain); + Assert.Equal(expectedLength, data.Length); + } + + #endregion + + #region Span Consistency After Expansions + + [Fact] + public async Task SpanConsistency_AfterCacheExpansion_LengthStillCorrect() + { + // ARRANGE + var cache = CreateCache(new WindowCacheOptions( + leftCacheSize: 2.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.3, + debounceDelay: TimeSpan.FromMilliseconds(50) + )); + + // ACT - First request establishes cache with expansion + var range1 = Intervals.NET.Factories.Range.Closed(100, 110); + var data1 = await cache.GetDataAsync(range1, CancellationToken.None); + + // Wait for background rebalance to complete + await cache.WaitForIdleAsync(); + + // Second request should hit expanded cache + var range2 = Intervals.NET.Factories.Range.Closed(105, 115); + var data2 = await cache.GetDataAsync(range2, CancellationToken.None); + + // ASSERT - Both requests return correct lengths despite cache expansion + Assert.Equal((int)range1.Span(_domain), data1.Length); + Assert.Equal((int)range2.Span(_domain), data2.Length); + } + + [Fact] + public async Task SpanConsistency_OverlappingRanges_EachReturnsCorrectLength() + { + // ARRANGE + var cache = CreateCache(); + var ranges = new[] + { + Intervals.NET.Factories.Range.Closed(100, 120), + Intervals.NET.Factories.Range.Closed(110, 130), + Intervals.NET.Factories.Range.Closed(115, 125) + }; + + // ACT & ASSERT - Each overlapping range returns exact length + foreach (var range in ranges) + { + var data = await cache.GetDataAsync(range, CancellationToken.None); + Assert.Equal((int)range.Span(_domain), data.Length); + } + } + + #endregion + + #region Exception Handling + + [Fact] + public async Task ExceptionHandling_CacheDoesNotThrow_UnlessDataSourceThrows() + { + // ARRANGE + var cache = CreateCache(); + var validRanges = new[] + { + Intervals.NET.Factories.Range.Closed(0, 10), + Intervals.NET.Factories.Range.Closed(1000, 2000), + Intervals.NET.Factories.Range.Closed(50, 51) + }; + + // ACT & ASSERT - No exceptions for valid ranges + foreach (var range in validRanges) + { + var exception = await Record.ExceptionAsync(async () => + await cache.GetDataAsync(range, CancellationToken.None)); + + Assert.Null(exception); + } + } + + #endregion + + #region Boundary Edge Cases + + [Fact] + public async Task BoundaryEdgeCase_ZeroCrossingRange_HandlesCorrectly() + { + // ARRANGE + var cache = CreateCache(); + var range = Intervals.NET.Factories.Range.Closed(-10, 10); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT + var array = data.ToArray(); + Assert.Equal(21, array.Length); // -10 to 10 inclusive + Assert.Equal(-10, array[0]); + Assert.Equal(0, array[10]); + Assert.Equal(10, array[20]); + } + + [Fact] + public async Task BoundaryEdgeCase_NegativeRange_ReturnsCorrectData() + { + // ARRANGE + var cache = CreateCache(); + var range = Intervals.NET.Factories.Range.Closed(-100, -90); + + // ACT + var data = await cache.GetDataAsync(range, CancellationToken.None); + + // ASSERT + var array = data.ToArray(); + Assert.Equal(11, array.Length); + Assert.Equal(-100, array[0]); + Assert.Equal(-90, array[^1]); + + // ASSERT - IDataSource handled negative range correctly + Assert.True(_dataSource.WasRangeCovered(-100, -90), + "DataSource should cover negative range [-100, -90]"); + Assert.True(_dataSource.TotalFetchCount > 0, "DataSource should be called"); + } + + #endregion +} diff --git a/tests/SlidingWindowCache.Integration.Tests/RebalanceExceptionHandlingTests.cs b/tests/SlidingWindowCache.Integration.Tests/RebalanceExceptionHandlingTests.cs new file mode 100644 index 0000000..eea5681 --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/RebalanceExceptionHandlingTests.cs @@ -0,0 +1,275 @@ +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Integration.Tests; + +/// +/// Tests for validating proper exception handling in background rebalance operations. +/// Demonstrates the critical importance of handling RebalanceExecutionFailed events. +/// +public class RebalanceExceptionHandlingTests : IDisposable +{ + private readonly EventCounterCacheDiagnostics _diagnostics; + + public RebalanceExceptionHandlingTests() + { + _diagnostics = new EventCounterCacheDiagnostics(); + } + + public void Dispose() + { + _diagnostics.Reset(); + } + + /// + /// Demonstrates that RebalanceExecutionFailed is properly recorded when data source throws during rebalance. + /// This validates that exceptions in background operations are caught and reported. + /// + [Fact] + public async Task RebalanceExecutionFailed_IsRecorded_WhenDataSourceThrowsDuringRebalance() + { + // Arrange: Create a data source that throws on the second fetch (during rebalance) + var callCount = 0; + var faultyDataSource = new FaultyDataSource( + fetchSingleRange: range => + { + callCount++; + if (callCount == 1) + { + // First call (user request) succeeds + return GenerateTestData(range); + } + // Second call (rebalance) fails + throw new InvalidOperationException("Simulated data source failure during rebalance"); + } + ); + + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.0, // Trigger rebalance immediately + rightThreshold: 0.0, + debounceDelay: TimeSpan.FromMilliseconds(10) + ); + + var cache = new WindowCache( + faultyDataSource, + new IntegerFixedStepDomain(), + options, + _diagnostics + ); + + // Act: Make a request that will trigger a rebalance + var data = await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + + // Wait for background rebalance to fail + await cache.WaitForIdleAsync(TimeSpan.FromSeconds(5)); + + // Assert: Verify the failure was recorded + Assert.Equal(1, _diagnostics.UserRequestServed); + Assert.Equal(1, _diagnostics.RebalanceIntentPublished); + Assert.Equal(1, _diagnostics.RebalanceExecutionStarted); + Assert.Equal(1, _diagnostics.RebalanceExecutionFailed); // ⚠️ This is the critical event + Assert.Equal(0, _diagnostics.RebalanceExecutionCompleted); // Should not complete + } + + /// + /// Demonstrates that user requests continue to work even after rebalance failures. + /// The cache remains operational despite background operation failures. + /// + [Fact] + public async Task UserRequests_ContinueToWork_AfterRebalanceFailure() + { + // Arrange: Create a data source that fails only during rebalance (second call) + var callCount = 0; + var partiallyFaultyDataSource = new FaultyDataSource( + fetchSingleRange: range => + { + callCount++; + if (callCount == 2) + { + // Second call (rebalance) fails + throw new InvalidOperationException("Rebalance fetch failed"); + } + // Other calls succeed + return GenerateTestData(range); + } + ); + + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.0, + rightThreshold: 0.0, + debounceDelay: TimeSpan.FromMilliseconds(10) + ); + + var cache = new WindowCache( + partiallyFaultyDataSource, + new IntegerFixedStepDomain(), + options, + _diagnostics + ); + + // Act: First request succeeds, triggers failed rebalance + var data1 = await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await cache.WaitForIdleAsync(TimeSpan.FromSeconds(5)); + + // Second request should still work (user path bypasses failed rebalance) + var data2 = await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(200, 210), CancellationToken.None); + await cache.WaitForIdleAsync(TimeSpan.FromSeconds(5)); + + // Assert: Both requests succeeded despite rebalance failure + Assert.Equal(2, _diagnostics.UserRequestServed); + Assert.Equal(11, data1.Length); + Assert.Equal(11, data2.Length); + + // Verify at least one rebalance failed + Assert.True(_diagnostics.RebalanceExecutionFailed >= 1, + "Expected at least one rebalance failure but got none. " + + "Without proper exception handling, this would have crashed the application."); + } + + /// + /// Demonstrates a production-ready diagnostics implementation with proper logging. + /// This is the recommended pattern for production applications. + /// + [Fact] + public async Task ProductionDiagnostics_ProperlyLogsRebalanceFailures() + { + // Arrange: Create a logging diagnostics implementation + var loggedExceptions = new List(); + var loggingDiagnostics = new LoggingCacheDiagnostics(ex => loggedExceptions.Add(ex)); + + var callCount = 0; + var faultyDataSource = new FaultyDataSource( + fetchSingleRange: range => + { + callCount++; + if (callCount == 1) + { + // First call (user request) succeeds + return GenerateTestData(range); + } + // Second call (rebalance) fails + throw new InvalidOperationException("Data source is unhealthy"); + } + ); + + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.0, + rightThreshold: 0.0, + debounceDelay: TimeSpan.FromMilliseconds(10) + ); + + var cache = new WindowCache( + faultyDataSource, + new IntegerFixedStepDomain(), + options, + loggingDiagnostics + ); + + // Act: Trigger a rebalance failure + await cache.GetDataAsync(Intervals.NET.Factories.Range.Closed(100, 110), CancellationToken.None); + await cache.WaitForIdleAsync(TimeSpan.FromSeconds(5)); + + // Assert: Exception was properly logged + Assert.True(loggedExceptions.Count >= 1, + "Production implementations MUST log all rebalance failures. " + + "Silent failures lead to degraded performance with no diagnostics."); + + var exception = loggedExceptions[0]; + Assert.IsType(exception); + Assert.Contains("Data source is unhealthy", exception.Message); + } + + #region Helper Classes + + /// + /// Faulty data source for testing exception handling. + /// + private class FaultyDataSource : IDataSource + where TRange : IComparable + { + private readonly Func, IEnumerable> _fetchSingleRange; + + public FaultyDataSource(Func, IEnumerable> fetchSingleRange) + { + _fetchSingleRange = fetchSingleRange; + } + + public Task> FetchAsync(Range range, CancellationToken cancellationToken) + { + var data = _fetchSingleRange(range); + return Task.FromResult(data); + } + + public Task> FetchAsync(IEnumerable> ranges, CancellationToken cancellationToken) + { + var allData = new List(); + foreach (var range in ranges) + { + var data = _fetchSingleRange(range); + allData.AddRange(data); + } + return Task.FromResult>(allData); + } + } + + /// + /// Production-ready diagnostics implementation that logs failures. + /// This demonstrates the minimum requirement for production use. + /// + private class LoggingCacheDiagnostics : ICacheDiagnostics + { + private readonly Action _logError; + + public LoggingCacheDiagnostics(Action logError) + { + _logError = logError; + } + + public void RebalanceExecutionFailed(Exception ex) + { + // ⚠️ CRITICAL: This is the minimum requirement for production + _logError(ex); + } + + // All other methods can be no-op if you only care about failures + public void UserRequestServed() { } + public void CacheExpanded() { } + public void CacheReplaced() { } + public void UserRequestFullCacheHit() { } + public void UserRequestPartialCacheHit() { } + public void UserRequestFullCacheMiss() { } + public void DataSourceFetchSingleRange() { } + public void DataSourceFetchMissingSegments() { } + public void RebalanceIntentPublished() { } + public void RebalanceIntentCancelled() { } + public void RebalanceExecutionStarted() { } + public void RebalanceExecutionCompleted() { } + public void RebalanceExecutionCancelled() { } + public void RebalanceSkippedNoRebalanceRange() { } + public void RebalanceSkippedSameRange() { } + } + + private static IEnumerable GenerateTestData(Intervals.NET.Range range) + { + var data = new List(); + for (var i = range.Start.Value; i <= range.End.Value; i++) + { + data.Add($"Item-{i}"); + } + return data; + } + + #endregion +} diff --git a/tests/SlidingWindowCache.Integration.Tests/SlidingWindowCache.Integration.Tests.csproj b/tests/SlidingWindowCache.Integration.Tests/SlidingWindowCache.Integration.Tests.csproj new file mode 100644 index 0000000..90c9f79 --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/SlidingWindowCache.Integration.Tests.csproj @@ -0,0 +1,31 @@ + + + + net8.0 + enable + enable + + false + true + + + + + + + + + + + + + + + + + + + + + + diff --git a/tests/SlidingWindowCache.Integration.Tests/TestInfrastructure/SpyDataSource.cs b/tests/SlidingWindowCache.Integration.Tests/TestInfrastructure/SpyDataSource.cs new file mode 100644 index 0000000..7334e06 --- /dev/null +++ b/tests/SlidingWindowCache.Integration.Tests/TestInfrastructure/SpyDataSource.cs @@ -0,0 +1,166 @@ +using System.Collections.Concurrent; +using Intervals.NET; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Dto; + +namespace SlidingWindowCache.Integration.Tests.TestInfrastructure; + +/// +/// A test spy/fake IDataSource implementation that records all fetch calls for verification. +/// Generates sequential integer data for requested ranges and tracks all interactions. +/// Thread-safe for concurrent test scenarios. +/// +public sealed class SpyDataSource : IDataSource +{ + private readonly ConcurrentBag> _singleFetchCalls = new(); + private readonly ConcurrentBag>> _batchFetchCalls = new(); + private int _totalFetchCount; + + /// + /// Total number of fetch operations (single + batch). + /// + public int TotalFetchCount => _totalFetchCount; + + /// + /// Resets all recorded calls. + /// + public void Reset() + { + _singleFetchCalls.Clear(); + _batchFetchCalls.Clear(); + Interlocked.Exchange(ref _totalFetchCount, 0); + } + + /// + /// Gets all ranges requested across both single and batch fetch calls. + /// Flattens batch calls into individual ranges. + /// + public IReadOnlyCollection> GetAllRequestedRanges() => + _batchFetchCalls + .SelectMany(b => b) + .Concat(_singleFetchCalls) + .ToList(); + + /// + /// Gets unique ranges requested (eliminates duplicates). + /// Useful for verifying no redundant identical fetches occurred. + /// + public IReadOnlyCollection> GetUniqueRequestedRanges() => + GetAllRequestedRanges() + .Distinct() + .ToList(); + + /// + /// Verifies that the requested range covers at least the specified boundaries. + /// Returns true if any requested range fully contains the target range. + /// + public bool WasRangeCovered(int start, int end) + { + foreach (var range in GetAllRequestedRanges()) + { + var rangeStart = (int)range.Start; + var rangeEnd = (int)range.End; + + // Check if this range fully covers [start, end] + if (rangeStart <= start && rangeEnd >= end) + { + return true; + } + } + + return false; + } + + /// + /// Asserts that a specific range was requested (boundary check). + /// + public void AssertRangeRequested(Range range) + { + Assert.Contains(GetAllRequestedRanges(), r => + r.Start == range.Start && + r.End == range.End && + range.IsStartInclusive == r.IsStartInclusive && + range.IsEndInclusive == r.IsEndInclusive); + } + + /// + /// Fetches data for a single range and records the call. + /// + public Task> FetchAsync(Range range, CancellationToken cancellationToken) + { + _singleFetchCalls.Add(range); + Interlocked.Increment(ref _totalFetchCount); + + var data = GenerateDataForRange(range); + return Task.FromResult>(data); + } + + /// + /// Fetches data for multiple ranges and records the call. + /// + public async Task>> FetchAsync( + IEnumerable> ranges, + CancellationToken cancellationToken) + { + var rangesList = ranges.ToList(); + _batchFetchCalls.Add(rangesList); + Interlocked.Increment(ref _totalFetchCount); + + var chunks = new List>(); + foreach (var range in rangesList) + { + var data = GenerateDataForRange(range); + chunks.Add(new RangeChunk(range, data)); + } + + return await Task.FromResult(chunks); + } + + /// + /// Generates sequential integer data for a range, respecting boundary inclusivity. + /// + private static List GenerateDataForRange(Range range) + { + var data = new List(); + var start = (int)range.Start; + var end = (int)range.End; + + switch (range) + { + case { IsStartInclusive: true, IsEndInclusive: true }: + // [start, end] + for (var i = start; i <= end; i++) + { + data.Add(i); + } + + break; + case { IsStartInclusive: true, IsEndInclusive: false }: + // [start, end) + for (var i = start; i < end; i++) + { + data.Add(i); + } + + break; + case { IsStartInclusive: false, IsEndInclusive: true }: + // (start, end] + for (var i = start + 1; i <= end; i++) + { + data.Add(i); + } + + break; + default: + // (start, end) + for (var i = start + 1; i < end; i++) + { + data.Add(i); + } + + break; + } + + return data; + } +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Invariants.Tests/README.md b/tests/SlidingWindowCache.Invariants.Tests/README.md new file mode 100644 index 0000000..bf0e14c --- /dev/null +++ b/tests/SlidingWindowCache.Invariants.Tests/README.md @@ -0,0 +1,411 @@ +# WindowCache Invariant Tests - Implementation Summary + +## Overview +Comprehensive unit test suite for the WindowCache library verifying system invariants through the public API using DEBUG-only instrumentation counters. + +**Architecture**: Single-Writer Model (User Path is read-only, Rebalance Execution is sole writer) + +**Test Statistics**: +- **Total Tests**: 27 automated tests (all passing) +- **Test Execution Time**: ~7 seconds for full suite +- **Architecture**: Single-writer with intent-carried data + +## Implementation Details + +### 1. Instrumentation Infrastructure +- **Location**: `src/SlidingWindowCache/Infrastructure/Instrumentation/` +- **Files**: + - `ICacheDiagnostics.cs` - Public interface for cache event tracking + - `EventCounterCacheDiagnostics.cs` - Thread-safe counter implementation + - Each counter includes XML documentation linking to specific invariants and usage locations + +- **Instrumented Components**: + - `WindowCache.cs` - No direct instrumentation (facade) + - `UserRequestHandler.cs` - Tracks user requests served (NO cache mutations - read-only) + - `IntentController.cs` - Tracks intent published/cancelled + - `RebalanceScheduler.cs` - Tracks execution started/completed/cancelled, policy-based skips + - `RebalanceExecutor.cs` - Tracks optimization-based skips (same-range detection) + +- **Counter Types** (with Invariant References): + - `UserRequestsServed` - User requests completed + - `CacheExpanded` - Range analysis determined expansion needed (called by shared CacheDataExtensionService) + - `CacheReplaced` - Range analysis determined replacement needed (called by shared CacheDataExtensionService) + - `RebalanceIntentPublished` - Rebalance intent published (every user request with delivered data) + - `RebalanceIntentCancelled` - Rebalance intent cancelled (new request supersedes old) + - `RebalanceExecutionStarted` - Rebalance execution began + - `RebalanceExecutionCompleted` - Rebalance execution finished successfully (sole writer) + - `RebalanceExecutionCancelled` - Rebalance execution cancelled + - `RebalanceSkippedNoRebalanceRange` - **Policy-based skip** (Invariant D.27) - Request within NoRebalanceRange threshold + - `RebalanceSkippedSameRange` - **Optimization-based skip** (Invariant D.28) - DesiredRange == CurrentRange + +**Note**: `CacheExpanded` and `CacheReplaced` are incremented during range analysis by the shared `CacheDataExtensionService` +(used by both User Path and Rebalance Path) when determining what data needs to be fetched. They track analysis/planning, +not actual cache mutations. Actual mutations only occur in Rebalance Execution via `Rematerialize()`. + +### 2. Deterministic Synchronization Infrastructure +- **Location**: `tests/SlidingWindowCache.Invariants.Tests/TestInfrastructure/` +- **Files Created**: + - `TestHelpers.cs` - Factory methods, data verification, and deterministic synchronization utilities + +- **Synchronization Strategy**: Deterministic Task Lifecycle Tracking + - **Method**: `WaitForRebalanceToSettleAsync(cache, timeout)` - Delegates to `cache.WaitForIdleAsync()` + - **Mechanism**: Observe-and-stabilize pattern based on Task reference tracking (not counter polling) + - **Benefits**: + - ✅ Race-free: No timing dependencies or polling intervals + - ✅ Deterministic: Guaranteed idle state when method returns + - ✅ Fast: Completes immediately when background work finishes + - ✅ Reliable: Works under concurrent intent cancellation and rescheduling + +- **Implementation Details**: + - **RebalanceScheduler** tracks latest background Task (`_idleTask` field) to support public WaitForIdleAsync() API + - **WaitForIdleAsync()** implements observe-and-stabilize loop: + 1. Read current `_idleTask` via `Volatile.Read` (ensures visibility) + 2. Await the observed Task + 3. Re-check if `_idleTask` changed (new rebalance scheduled) + 4. Loop until Task reference stabilizes and completes + - This implementation exists in all builds to support the public infrastructure API for testing, graceful shutdown, and health checks + +- **Old Approach (Removed)**: + - Counter-based polling with stability windows + - Timing-dependent with configurable intervals + - Complex lifecycle tracking logic + - Replaced by deterministic Task tracking + +- **Domain Strategy**: Uses `Intervals.NET.Domain.Default.Numeric.IntegerFixedStepDomain` for proper range handling with inclusivity support + +- **Mock Strategy**: Uses **Moq** framework for `IDataSource` mocking + - Mock configured per-test in Arrange section + - Generates sequential integer data respecting range inclusivity + - Supports configurable fetch delays for cancellation testing + - Properly calculates range spans using Intervals.NET domain + +### 3. Test Project Configuration +- **Updated**: `SlidingWindowCache.Invariants.Tests.csproj` +- **Added Dependencies**: + - `Moq` (Version 4.20.70) - For IDataSource mocking + - `xUnit` - Test framework + - `Intervals.NET` packages - Domain and range handling + - Project reference to `SlidingWindowCache` +- **Framework**: xUnit with standard `Assert` class (not FluentAssertions - decision for consistency) + +### 4. Comprehensive Test Suite +- **Location**: `tests/SlidingWindowCache.Invariants.Tests/WindowCacheInvariantTests.cs` +- **Test Count**: 27 invariant tests + 1 execution lifecycle meta-invariant +- **Test Structure**: Each test method references its invariant number and description + +#### Test Categories: + +**A. User Path & Fast User Access (8 tests)** +- A.1-0a: User request cancels rebalance (to prevent interference, not for mutation safety) +- A.2.1: User path always serves requests +- A.2.2: User path never waits for rebalance +- A.2.10: User always receives exact requested range +- A.3.8: Cold start - User Path does NOT populate cache (read-only) +- A.3.8: Cache expansion - User Path does NOT expand cache (read-only) +- A.3.8: Full cache replacement - User Path does NOT replace cache (read-only) +- A.3.9a: Cache contiguity maintained + +**B. Cache State & Consistency (2 tests)** +- B.11: CacheData and CurrentCacheRange always consistent +- B.15: Cancelled rebalance doesn't violate consistency + +**C. Rebalance Intent & Temporal (4 tests)** +- C.17: At most one active intent +- C.18: Previous intent becomes obsolete +- C.24: Intent doesn't guarantee execution (opportunistic) +- C.23: System stabilizes under load + +**D. Rebalance Decision Path (2 tests + TODOs)** +- D.27: No rebalance if request in NoRebalanceRange (policy-based skip) - **Enhanced with execution started assertion** +- D.28: Rebalance skipped when DesiredRange == CurrentRange (optimization-based skip) - **New test** +- TODOs for D.25, D.26, D.29 (require internal state access) + +**E. Cache Geometry & Policy (1 test + TODOs)** +- E.30: DesiredRange computed from config and request +- TODOs for E.31-34 (require internal state inspection) + +**F. Rebalance Execution (3 tests)** +- F.35, F.35a: Rebalance execution supports cancellation +- F.36a: Rebalance normalizes cache - **Enhanced with lifecycle integrity assertions** +- F.40-42: Post-execution guarantees + +**G. Execution Context & Scheduling (2 tests)** +- G.43-45: Execution context separation +- G.46: Cancellation supported for all scenarios + +**Meta-Invariant Tests (1 test)** +- Execution lifecycle integrity: started == (completed + cancelled) - **New test** + +**Additional Comprehensive Tests (3 tests)** +- Complete scenario with multiple requests and rebalancing +- Concurrency scenario with rapid request bursts and cancellation +- Read mode variations (Snapshot and CopyOnRead) + +### 5. Key Implementation Changes (Single-Writer Architecture Migration) + +**UserRequestHandler.cs**: +- **REMOVED**: All `_state.Cache.Rematerialize()` calls (User Path is now read-only) +- **REMOVED**: `_state.LastRequested` writes (only Rebalance Execution writes) +- **ADDED**: Cold start detection using cache data enumeration +- **ADDED**: Materialization of assembled data to array (for user + intent) +- **ADDED**: Creation of `RangeData` for intent with delivered data +- **PRESERVED**: Cancellation logic (User Path priority) +- **PRESERVED**: Cache hit detection and read logic +- **PRESERVED**: IDataSource fetching for missing data + +**IntentController.cs & RebalanceScheduler.cs**: +- **ADDED**: `RangeData deliveredData` parameter to intent +- **ADDED**: Intent now carries both requested range and actual delivered data +- **PURPOSE**: Enables Rebalance Execution to use delivered data as authoritative source + +**RebalanceExecutor.cs**: +- **ADDED**: Accept `requestedRange` and `deliveredData` parameters +- **CHANGED**: Uses delivered data from intent as base (not current cache) +- **ADDED**: Writes to `_state.LastRequested` (sole writer) +- **ADDED**: Writes to `_state.NoRebalanceRange` (already was sole writer) +- **RESPONSIBILITY**: Sole writer of all cache state (Cache, LastRequested, NoRebalanceRange) + +**CacheState.cs**: +- **CHANGED**: `LastRequested` and `NoRebalanceRange` setters to `internal` +- **PURPOSE**: Enforce single-writer pattern at compile time + +**Storage Classes**: +- **CopyOnReadStorage.cs**: Refactored to use dual-buffer (staging buffer) pattern for safe rematerialization + - Active buffer remains immutable during reads + - Staging buffer used for new range data during rematerialization + - Atomic buffer swap after rematerialization completes + - Prevents enumeration issues when concatenating existing + new data +- **SnapshotReadStorage.cs**: No changes needed - already uses safe rematerialization pattern + +### 6. Test Execution +- **Build Configuration**: DEBUG mode (required for instrumentation and Task tracking) +- **Reset Pattern**: Each test resets counters in constructor/dispose +- **Synchronization**: Uses deterministic `cache.WaitForIdleAsync()` for race-free background work completion +- **Data Verification**: Custom helper verifies returned data matches expected range values + +## Invariants Coverage + +### Single-Writer Architecture + +**Key Architectural Change**: +- **User Path**: Read-only with respect to cache state (never mutates) +- **Rebalance Execution**: Sole writer of all cache state +- **Intent Structure**: Contains both requested range and delivered data (`RangeData`) +- **Concurrency**: Single-writer eliminates race conditions + +### Test Coverage Breakdown + +**User Path Tests (8 tests - verify read-only behavior)**: +- User Path serves requests without mutating cache +- User Path cancels rebalance to prevent interference (not for mutation safety) +- User Path returns correct data immediately +- User Path publishes intent with delivered data +- Cache mutations occur exclusively via Rebalance Execution + +**Rebalance Execution Tests (verify single-writer)**: +- Rebalance Execution is sole writer of cache state +- Rebalance Execution uses delivered data from intent +- Rebalance Execution handles cancellation properly +- Cache state converges asynchronously (eventual consistency) + +**Architectural Invariants (enforced by code structure)**: +- A.-1: User Path and Rebalance Execution never write concurrently (User Path doesn't write) +- A.8: User Path MUST NOT mutate cache (enforced by removing Rematerialize calls) +- F.36: Rebalance Execution is ONLY writer (enforced by internal setters) +- C.24e/f: Intent contains delivered data (enforced by PublishIntent signature) + +## Usage + +```bash +# Run all invariant tests +dotnet test tests/SlidingWindowCache.Invariants.Tests/SlidingWindowCache.Invariants.Tests.csproj --configuration Debug + +# Run specific test +dotnet test --filter "FullyQualifiedName~Invariant_D28_SkipWhenDesiredEqualsCurrentRange" + +# Run tests by category (example: all Decision Path tests) +dotnet test --filter "FullyQualifiedName~Invariant_D" +``` + +## Key Implementation Details + +### Skip Condition Distinction +The system has **two distinct skip scenarios**, tracked by separate counters: + +1. **Policy-Based Skip** (Invariant D.27) + - Counter: `RebalanceSkippedNoRebalanceRange` + - Location: `RebalanceScheduler` (after `DecisionEngine` returns `ShouldExecute=false`) + - Reason: Request within NoRebalanceRange threshold zone + - Characteristic: Execution **never starts** (decision-level optimization) + +2. **Optimization-Based Skip** (Invariant D.28) + - Counter: `RebalanceSkippedSameRange` + - Location: `RebalanceExecutor.ExecuteAsync` (before I/O operations) + - Reason: `CurrentCacheRange == DesiredCacheRange` (already at target) + - Characteristic: Execution **starts but exits early** (executor-level optimization) + +### CopyOnRead Storage - Staging Buffer Pattern +The `CopyOnReadStorage` implementation uses a dual-buffer approach for safe rematerialization: +- **Active buffer**: Immutable during reads, serves user requests +- **Staging buffer**: Write-only during rematerialization, reused across operations +- **Atomic swap**: After successful rematerialization, buffers are swapped +- **Rationale**: Prevents enumeration issues when concatenating existing + new data ranges + +This pattern ensures: +- Active storage remains immutable during reads (no lock needed for single-consumer model) +- Predictable memory allocation behavior +- No temporary allocations beyond the staging buffer + +See `docs/storage-strategies.md` for detailed documentation. + +## Notes +- **Architecture**: Single-writer model (User Path read-only, Rebalance Execution sole writer) +- **Intent Structure**: Intent carries delivered `RangeData` (requested range + actual data) +- **Eventual Consistency**: Cache state converges asynchronously via background rebalance +- Instrumentation is DEBUG-only using `[Conditional("DEBUG")]` attributes - zero overhead in Release builds +- Tests use timing-based async verification with `WaitForRebalanceAsync()` helper +- Counter reset in constructor/dispose ensures test isolation +- Uses `Intervals.NET.Domain.Default.Numeric.IntegerFixedStepDomain` for proper range inclusivity handling +- `CacheExpanded` and `CacheReplaced` counters are deprecated (User Path no longer mutates) + +## Related Documentation +- `docs/invariants.md` - Complete invariant documentation (updated for single-writer architecture) +- `docs/cache-state-machine.md` - State transitions (updated to show only Rebalance Execution mutates) +- `docs/actors-and-responsibilities.md` - Component responsibilities (updated for read-only User Path) +- `docs/concurrency-model.md` - Single-writer architecture and eventual consistency model +- `MIGRATION_SUMMARY.md` - Implementation details of single-writer migration +- `DOCUMENTATION_UPDATES.md` - Documentation changes made for new architecture + +## Test Infrastructure + +All tests use: +1. **`WaitForIdleAsync()`** - Deterministic synchronization with background rebalance (available in all builds) +2. **`CacheInstrumentationCounters`** (DEBUG-only) - Observable event counters for validation +3. **`TestHelpers`** - Test data builders and common assertion patterns + +## Diagnostic Usage in Tests + +All tests leverage `EventCounterCacheDiagnostics` for observable validation of cache behavior: + +```csharp +private readonly EventCounterCacheDiagnostics _cacheDiagnostics; + +public WindowCacheInvariantTests() +{ + _cacheDiagnostics = new EventCounterCacheDiagnostics(); +} +``` + +### Purpose of Diagnostics in Tests + +1. **Observable State**: Tracks internal behavioral events without invasive test hooks +2. **Invariant Validation**: Verifies system invariants through event patterns +3. **Scenario Verification**: Confirms expected cache scenarios (hit/miss patterns, rebalance lifecycle) +4. **Test Isolation**: `Reset()` method ensures clean state between test phases + +### Common Assertion Patterns + +**User Path Scenario Validation:** +```csharp +// Verify full cache hit +TestHelpers.AssertFullCacheHit(_cacheDiagnostics, expectedCount: 1); + +// Verify partial cache hit with extension +TestHelpers.AssertPartialCacheHit(_cacheDiagnostics, expectedCount: 1); + +// Verify full cache miss (cold start or jump) +TestHelpers.AssertFullCacheMiss(_cacheDiagnostics, expectedCount: 1); +``` + +**Rebalance Lifecycle Validation:** +```csharp +// Verify rebalance lifecycle integrity (started == completed + cancelled) +TestHelpers.AssertRebalanceLifecycleIntegrity(_cacheDiagnostics); + +// Verify rebalance completed successfully +TestHelpers.AssertRebalanceCompleted(_cacheDiagnostics, minExpected: 1); + +// Verify rebalance was cancelled by new user request +TestHelpers.AssertRebalancePathCancelled(_cacheDiagnostics, minExpected: 1); +``` + +**Data Source Interaction Validation:** +```csharp +// Verify single-range fetch (cold start or jump) +TestHelpers.AssertDataSourceFetchedFullRange(_cacheDiagnostics, expectedCount: 1); + +// Verify missing-segments fetch (partial hit optimization) +TestHelpers.AssertDataSourceFetchedMissingSegments(_cacheDiagnostics, expectedCount: 1); +``` + +**Test Isolation with Reset():** +```csharp +// Setup phase +await cache.GetDataAsync(Range.Closed(100, 200), ct); +await cache.WaitForIdleAsync(); + +// Reset counters to isolate test scenario +_cacheDiagnostics.Reset(); + +// Test phase - only this scenario's events are tracked +await cache.GetDataAsync(Range.Closed(120, 180), ct); + +// Assert only test scenario events +Assert.Equal(1, _cacheDiagnostics.UserRequestFullCacheHit); +Assert.Equal(0, _cacheDiagnostics.UserRequestPartialCacheHit); +``` + +### Integration with WaitForIdleAsync() + +Diagnostics and `WaitForIdleAsync()` work together for complete test determinism: + +```csharp +// 1. Perform action +await cache.GetDataAsync(Range.Closed(100, 200), ct); + +// 2. Wait for rebalance to complete (deterministic synchronization) +await cache.WaitForIdleAsync(); + +// 3. Assert using diagnostics (observable validation) +Assert.Equal(1, _cacheDiagnostics.RebalanceExecutionCompleted); +TestHelpers.AssertRebalanceLifecycleIntegrity(_cacheDiagnostics); +``` + +**Key Distinction:** +- **`WaitForIdleAsync()`**: Synchronization mechanism (when to assert) +- **Diagnostics**: Observable state (what to assert) + +### Available Diagnostic Counters + +**User Path Events:** +- `UserRequestServed` - Total requests completed +- `CacheExpanded` - Cache expansion operations +- `CacheReplaced` - Cache replacement operations +- `UserRequestFullCacheHit` - Full cache hits +- `UserRequestPartialCacheHit` - Partial cache hits +- `UserRequestFullCacheMiss` - Full cache misses + +**Data Source Events:** +- `DataSourceFetchSingleRange` - Single-range fetches +- `DataSourceFetchMissingSegments` - Multi-segment fetches + +**Rebalance Lifecycle:** +- `RebalanceIntentPublished` - Intents published +- `RebalanceIntentCancelled` - Intents cancelled +- `RebalanceExecutionStarted` - Executions started +- `RebalanceExecutionCompleted` - Executions completed +- `RebalanceExecutionCancelled` - Executions cancelled +- `RebalanceSkippedNoRebalanceRange` - Skipped due to policy +- `RebalanceSkippedSameRange` - Skipped due to optimization + +### Helper Assertion Library + +See `TestHelpers.cs` for complete assertion library including: +- `AssertNoUserPathMutations()` - Verify User Path is read-only +- `AssertIntentPublished()` - Verify intent publication +- `AssertRebalanceLifecycleIntegrity()` - Verify lifecycle invariants +- `AssertRebalanceSkippedDueToPolicy()` - Verify skip optimization +- `AssertFullCacheHit/PartialCacheHit/FullCacheMiss()` - Verify user scenarios +- `AssertDataSourceFetchedFullRange/MissingSegments()` - Verify data source interaction + +**See**: [Diagnostics Guide](../../docs/diagnostics.md) for comprehensive diagnostic API reference \ No newline at end of file diff --git a/tests/SlidingWindowCache.Invariants.Tests/SlidingWindowCache.Invariants.Tests.csproj b/tests/SlidingWindowCache.Invariants.Tests/SlidingWindowCache.Invariants.Tests.csproj new file mode 100644 index 0000000..3e6abce --- /dev/null +++ b/tests/SlidingWindowCache.Invariants.Tests/SlidingWindowCache.Invariants.Tests.csproj @@ -0,0 +1,28 @@ + + + + net8.0 + enable + enable + + false + true + + + + + + + + + + + + + + + + + + + diff --git a/tests/SlidingWindowCache.Invariants.Tests/TestInfrastructure/TestHelpers.cs b/tests/SlidingWindowCache.Invariants.Tests/TestInfrastructure/TestHelpers.cs new file mode 100644 index 0000000..1d631f3 --- /dev/null +++ b/tests/SlidingWindowCache.Invariants.Tests/TestInfrastructure/TestHelpers.cs @@ -0,0 +1,404 @@ +using Intervals.NET; +using Intervals.NET.Domain.Default.Numeric; +using Intervals.NET.Domain.Extensions.Fixed; +using Moq; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; +using SlidingWindowCache.Public.Dto; + +namespace SlidingWindowCache.Invariants.Tests.TestInfrastructure; + +/// +/// Helper methods for creating test components. +/// Uses Intervals.NET packages for proper range handling and domain calculations. +/// +public static class TestHelpers +{ + /// + /// Creates a standard integer fixed-step domain for testing. + /// + public static IntegerFixedStepDomain CreateIntDomain() => new(); + + /// + /// Creates a closed range [start, end] (both boundaries inclusive) using Intervals.NET factory. + /// This is the standard range type used throughout the WindowCache system. + /// + /// The start value (inclusive). + /// The end value (inclusive). + /// A closed range [start, end]. + public static Range CreateRange(int start, int end) => Intervals.NET.Factories.Range.Closed(start, end); + + /// + /// Creates default cache options for testing. + /// + public static WindowCacheOptions CreateDefaultOptions( + double leftCacheSize = 1.0, // The left cache size equals to the requested range size + double rightCacheSize = 1.0, // The right cache size equals to the requested range size + double? leftThreshold = 0.2, // 20% threshold on the left side + double? rightThreshold = 0.2, // 20% threshold on the right side + TimeSpan? debounceDelay = null, // Default debounce delay of 50ms + UserCacheReadMode readMode = UserCacheReadMode.Snapshot + ) => new( + leftCacheSize: leftCacheSize, + rightCacheSize: rightCacheSize, + readMode: readMode, + leftThreshold: leftThreshold, + rightThreshold: rightThreshold, + debounceDelay: debounceDelay ?? TimeSpan.FromMilliseconds(50) + ); + + /// + /// Calculates the expected desired cache range using the same logic as ProportionalRangePlanner. + /// This helper ensures tests verify the actual planner behavior rather than hardcoding imagined values. + /// + /// The range requested by the user. + /// The cache options containing leftCacheSize and rightCacheSize. + /// The domain for range calculations. + /// The expected desired cache range after expansion. + public static Range CalculateExpectedDesiredRange( + Range requestedRange, + WindowCacheOptions options, + IntegerFixedStepDomain domain) + { + // Mimic ProportionalRangePlanner.Plan() logic + var size = requestedRange.Span(domain); + var left = (long)(size.Value * options.LeftCacheSize); + var right = (long)(size.Value * options.RightCacheSize); + + return requestedRange.Expand(domain, left, right); + } + + /// + /// Verifies that the data matches the expected range values using Intervals.NET domain calculations. + /// Properly handles range inclusivity. + /// + public static void VerifyDataMatchesRange(ReadOnlyMemory data, Range expectedRange) + { + var span = data.Span; + + // Use Intervals.NET domain to calculate expected length + var domain = new IntegerFixedStepDomain(); + var expectedLength = (int)expectedRange.Span(domain); + + Assert.Equal(expectedLength, span.Length); + + // Verify data values match the range + var start = (int)expectedRange.Start; + + switch (expectedRange) + { + // For closed ranges [start, end], data should be sequential from start + case { IsStartInclusive: true, IsEndInclusive: true }: + { + for (var i = 0; i < span.Length; i++) + { + Assert.Equal(start + i, span[i]); + } + + break; + } + case { IsStartInclusive: true, IsEndInclusive: false }: + { + // [start, end) - start inclusive, end exclusive + for (var i = 0; i < span.Length; i++) + { + Assert.Equal(start + i, span[i]); + } + + break; + } + case { IsStartInclusive: false, IsEndInclusive: true }: + { + // (start, end] - start exclusive, end inclusive + for (var i = 0; i < span.Length; i++) + { + Assert.Equal(start + 1 + i, span[i]); + } + + break; + } + default: + { + // (start, end) - both exclusive + for (var i = 0; i < span.Length; i++) + { + Assert.Equal(start + 1 + i, span[i]); + } + + break; + } + } + } + + /// + /// Creates a mock IDataSource that generates sequential integer data for any requested range. + /// Properly handles range inclusivity using Intervals.NET domain calculations. + /// + public static Mock> CreateMockDataSource(IntegerFixedStepDomain domain, + TimeSpan? fetchDelay = null) + { + var mock = new Mock>(); + + mock.Setup(ds => ds.FetchAsync(It.IsAny>(), It.IsAny())) + .Returns, CancellationToken>(async (range, ct) => + { + if (fetchDelay.HasValue) + { + await Task.Delay(fetchDelay.Value, ct); + } + + // Use Intervals.NET domain to properly calculate range span + var span = range.Span(domain); + var data = new List((int)span); + + // Generate data respecting range inclusivity + var start = (int)range.Start; + var end = (int)range.End; + + switch (range) + { + case { IsStartInclusive: true, IsEndInclusive: true }: + for (var i = start; i <= end; i++) + { + data.Add(i); + } + + break; + case { IsStartInclusive: true, IsEndInclusive: false }: + for (var i = start; i < end; i++) + { + data.Add(i); + } + + break; + case { IsStartInclusive: false, IsEndInclusive: true }: + for (var i = start + 1; i <= end; i++) + { + data.Add(i); + } + + break; + default: + for (var i = start + 1; i < end; i++) + { + data.Add(i); + } + + break; + } + + return data; + }); + + mock.Setup(ds => ds.FetchAsync(It.IsAny>>(), It.IsAny())) + .Returns>, CancellationToken>(async (ranges, ct) => + { + var chunks = new List>(); + + foreach (var range in ranges) + { + var data = await mock.Object.FetchAsync(range, ct); + chunks.Add(new RangeChunk(range, data)); + } + + return chunks; + }); + + return mock; + } + + /// + /// Creates a WindowCache instance with the specified options. + /// + public static WindowCache CreateCache( + Mock> mockDataSource, + IntegerFixedStepDomain domain, + WindowCacheOptions options, + EventCounterCacheDiagnostics cacheDiagnostics) => + new(mockDataSource.Object, domain, options, cacheDiagnostics); + + /// + /// Creates a WindowCache with default options and returns both cache and mock data source. + /// + public static (WindowCache cache, Mock> mock) + CreateCacheWithDefaults( + IntegerFixedStepDomain domain, + EventCounterCacheDiagnostics cacheDiagnostics, + WindowCacheOptions? options = null, + TimeSpan? fetchDelay = null + ) + { + var mock = CreateMockDataSource(domain, fetchDelay); + var cache = CreateCache(mock, domain, options ?? CreateDefaultOptions(), cacheDiagnostics); + return (cache, mock); + } + + /// + /// Executes a request and waits for rebalance to complete before returning. + /// + public static async Task> ExecuteRequestAndWaitForRebalance( + WindowCache cache, + Range range) + { + var data = await cache.GetDataAsync(range, CancellationToken.None); + await cache.WaitForIdleAsync(); + return data; + } + + /// + /// Asserts that user received correct data matching the requested range. + /// + public static void AssertUserDataCorrect(ReadOnlyMemory data, Range range) + { + VerifyDataMatchesRange(data, range); + } + + /// + /// Asserts that User Path did not trigger cache extension analysis (single-writer architecture). + /// + /// + /// Note: CacheExpanded and CacheReplaced counters are incremented by the shared CacheDataExtensionService + /// during range analysis (when determining what data needs to be fetched). They track planning, not actual + /// cache mutations. This assertion verifies that User Path didn't call ExtendCacheAsync, which would + /// increment these counters. Actual cache mutations (via Rematerialize) only occur in Rebalance Execution. + /// + /// In test scenarios, prior rebalance operations typically expand the cache enough that subsequent + /// User Path requests are full hits, avoiding calls to ExtendCacheAsync entirely. + /// + public static void AssertNoUserPathMutations(EventCounterCacheDiagnostics cacheDiagnostics) + { + Assert.Equal(0, cacheDiagnostics.CacheExpanded); + Assert.Equal(0, cacheDiagnostics.CacheReplaced); + } + + /// + /// Asserts that rebalance intent was published. + /// + public static void AssertIntentPublished(EventCounterCacheDiagnostics cacheDiagnostics, int expectedCount = -1) + { + if (expectedCount >= 0) + { + Assert.Equal(expectedCount, cacheDiagnostics.RebalanceIntentPublished); + } + else + { + Assert.True(cacheDiagnostics.RebalanceIntentPublished > 0, + $"Intent should be published, but actual count was {cacheDiagnostics.RebalanceIntentPublished}"); + } + } + + /// + /// Asserts that rebalance was cancelled (at either intent or execution stage). + /// + /// + /// + /// Due to timing, cancellation can occur at two distinct lifecycle points: + /// + /// + /// + /// Intent-level cancellation: When a new request arrives while the previous + /// rebalance is still in debounce delay (before execution starts). This increments + /// . + /// + /// + /// Execution-level cancellation: When a new request arrives after the debounce + /// delay completed and execution has started. This increments + /// . + /// + /// + /// + /// This method checks the total cancellations across both stages, making assertions + /// stable regardless of timing variations. Most tests care that cancellation occurred, not the + /// specific lifecycle stage where it happened. + /// + /// + /// + /// The diagnostics instance to check for cancellation counts. The method will sum both intent and execution cancellations to determine if the expected number of cancellations occurred. + /// + /// Minimum number of total cancellations expected (default: 1). + public static void AssertRebalancePathCancelled(EventCounterCacheDiagnostics cacheDiagnostics, int minExpected = 1) + { + var totalCancelled = cacheDiagnostics.RebalanceIntentCancelled + + cacheDiagnostics.RebalanceExecutionCancelled; + Assert.True(totalCancelled >= minExpected, + $"At least {minExpected} cancellation(s) expected (intent or execution), but actual count was {totalCancelled} " + + $"(IntentCancelled: {cacheDiagnostics.RebalanceIntentCancelled}, " + + $"ExecutionCancelled: {cacheDiagnostics.RebalanceExecutionCancelled})"); + } + + /// + /// Asserts rebalance execution lifecycle integrity: Started == Completed + Cancelled. + /// + public static void AssertRebalanceLifecycleIntegrity(EventCounterCacheDiagnostics cacheDiagnostics) + { + var started = cacheDiagnostics.RebalanceExecutionStarted; + var completed = cacheDiagnostics.RebalanceExecutionCompleted; + var executionsCancelled = cacheDiagnostics.RebalanceExecutionCancelled; + Assert.Equal(started, completed + executionsCancelled); + } + + /// + /// Asserts that rebalance was skipped due to NoRebalanceRange policy. + /// + public static void AssertRebalanceSkippedDueToPolicy(EventCounterCacheDiagnostics cacheDiagnostics) + { + var skipped = cacheDiagnostics.RebalanceSkippedNoRebalanceRange; + Assert.True(skipped > 0, + $"Expected at least one rebalance to be skipped due to NoRebalanceRange policy, but found {skipped}."); + + Assert.Equal(0, cacheDiagnostics.RebalanceExecutionStarted); + Assert.Equal(0, cacheDiagnostics.RebalanceExecutionCompleted); + } + + /// + /// Asserts that rebalance execution completed successfully. + /// + public static void AssertRebalanceCompleted(EventCounterCacheDiagnostics cacheDiagnostics, int minExpected = 1) + { + Assert.True(cacheDiagnostics.RebalanceExecutionCompleted >= minExpected, + $"Rebalance should have completed at least {minExpected} time(s), but actual count was {cacheDiagnostics.RebalanceExecutionCompleted}"); + } + + /// + /// Asserts that the request resulted in a full cache hit (all data served from cache). + /// + public static void AssertFullCacheHit(EventCounterCacheDiagnostics cacheDiagnostics, int expectedCount = 1) + { + Assert.Equal(expectedCount, cacheDiagnostics.UserRequestFullCacheHit); + } + + /// + /// Asserts that the request resulted in a partial cache hit (some data from cache, some from data source). + /// + public static void AssertPartialCacheHit(EventCounterCacheDiagnostics cacheDiagnostics, int expectedCount = 1) + { + Assert.Equal(expectedCount, cacheDiagnostics.UserRequestPartialCacheHit); + } + + /// + /// Asserts that the request resulted in a full cache miss (all data fetched from data source). + /// + public static void AssertFullCacheMiss(EventCounterCacheDiagnostics cacheDiagnostics, int expectedCount = 1) + { + Assert.Equal(expectedCount, cacheDiagnostics.UserRequestFullCacheMiss); + } + + /// + /// Asserts that data was fetched from data source for a complete range (cold start or full miss). + /// + public static void AssertDataSourceFetchedFullRange(EventCounterCacheDiagnostics cacheDiagnostics, + int expectedCount = 1) + { + Assert.Equal(expectedCount, cacheDiagnostics.DataSourceFetchSingleRange); + } + + /// + /// Asserts that data was fetched from data source for missing segments only (partial hit optimization). + /// + public static void AssertDataSourceFetchedMissingSegments(EventCounterCacheDiagnostics cacheDiagnostics, + int expectedCount = 1) + { + Assert.Equal(expectedCount, cacheDiagnostics.DataSourceFetchMissingSegments); + } +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Invariants.Tests/WindowCacheInvariantTests.cs b/tests/SlidingWindowCache.Invariants.Tests/WindowCacheInvariantTests.cs new file mode 100644 index 0000000..8d82f14 --- /dev/null +++ b/tests/SlidingWindowCache.Invariants.Tests/WindowCacheInvariantTests.cs @@ -0,0 +1,857 @@ +using Intervals.NET.Domain.Default.Numeric; +using Intervals.NET.Domain.Extensions.Fixed; +using Intervals.NET.Extensions; +using SlidingWindowCache.Infrastructure.Instrumentation; +using SlidingWindowCache.Invariants.Tests.TestInfrastructure; +using SlidingWindowCache.Public; +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Invariants.Tests; + +/// +/// Comprehensive test suite verifying all 47 system invariants for WindowCache. +/// Each test references its corresponding invariant number and description. +/// Tests use DEBUG instrumentation counters to verify behavioral properties. +/// Uses Intervals.NET for proper range handling and inclusivity considerations. +/// +public sealed class WindowCacheInvariantTests : IAsyncDisposable +{ + private readonly IntegerFixedStepDomain _domain; + private WindowCache? _currentCache; + private readonly EventCounterCacheDiagnostics _cacheDiagnostics; + + public WindowCacheInvariantTests() + { + _cacheDiagnostics = new EventCounterCacheDiagnostics(); + _domain = TestHelpers.CreateIntDomain(); + } + + /// + /// Ensures any background rebalance operations are completed before executing next test + /// + public async ValueTask DisposeAsync() + { + // Wait for any background rebalance from current test to complete + await _currentCache!.WaitForIdleAsync(); + } + + /// + /// Tracks a cache instance for automatic cleanup in Dispose. + /// + private (WindowCache cache, Moq.Mock> mockDataSource) + TrackCache( + (WindowCache cache, Moq.Mock> mockDataSource) tuple) + { + _currentCache = tuple.cache; + return tuple; + } + + #region A. User Path & Fast User Access Invariants + + #region A.1 Concurrency & Priority + + /// + /// Tests Invariant A.0a (🟢 Behavioral): Every User Request MUST cancel any ongoing or pending + /// Rebalance Execution to ensure rebalance doesn't interfere with User Path data assembly. + /// Verifies cancellation via DEBUG instrumentation counters. + /// Related: A.0 (Architectural - User Path has higher priority than Rebalance Execution) + /// + [Fact] + public async Task Invariant_A_0a_UserRequestCancelsRebalance() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 2.0, rightCacheSize: 2.0, + debounceDelay: TimeSpan.FromMilliseconds(100)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: First request triggers rebalance intent + await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + var intentPublishedBefore = _cacheDiagnostics.RebalanceIntentPublished; + Assert.Equal(1, intentPublishedBefore); + + // Second request cancels the first rebalance intent + await cache.GetDataAsync(TestHelpers.CreateRange(120, 130), CancellationToken.None); + + // Wait for background rebalance to settle before checking counters + await cache.WaitForIdleAsync(); + + // ASSERT: Verify cancellation occurred + TestHelpers.AssertRebalancePathCancelled(_cacheDiagnostics); + } + + #endregion + + #region A.2 User-Facing Guarantees + + /// + /// Tests Invariant A.1 (🟢 Behavioral): User Path always serves user requests regardless + /// of rebalance execution state. Validates core guarantee that users are never blocked by cache maintenance. + /// + [Fact] + public async Task Invariant_A2_1_UserPathAlwaysServesRequests() + { + // ARRANGE + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics)); + + // ACT: Make multiple requests + var data1 = await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + var data2 = await cache.GetDataAsync(TestHelpers.CreateRange(200, 210), CancellationToken.None); + var data3 = await cache.GetDataAsync(TestHelpers.CreateRange(105, 115), CancellationToken.None); + + // ASSERT: All requests completed with correct data + TestHelpers.AssertUserDataCorrect(data1, TestHelpers.CreateRange(100, 110)); + TestHelpers.AssertUserDataCorrect(data2, TestHelpers.CreateRange(200, 210)); + TestHelpers.AssertUserDataCorrect(data3, TestHelpers.CreateRange(105, 115)); + Assert.Equal(3, _cacheDiagnostics.UserRequestServed); + } + + /// + /// Tests Invariant A.2 (🟢 Behavioral): User Path never waits for rebalance execution to complete. + /// Verifies requests complete quickly without waiting for debounce delay or background rebalance. + /// + [Fact] + public async Task Invariant_A2_2_UserPathNeverWaitsForRebalance() + { + // ARRANGE: Cache with slow rebalance (1s debounce) + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromSeconds(1)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Request completes immediately without waiting for rebalance + var stopwatch = System.Diagnostics.Stopwatch.StartNew(); + var data = await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + stopwatch.Stop(); + + // ASSERT: Request completed quickly (much less than debounce delay) + Assert.Equal(1, _cacheDiagnostics.UserRequestServed); + Assert.Equal(1, _cacheDiagnostics.RebalanceIntentPublished); + Assert.Equal(0, _cacheDiagnostics.RebalanceExecutionCompleted); + TestHelpers.AssertUserDataCorrect(data, TestHelpers.CreateRange(100, 110)); + await cache.WaitForIdleAsync(); + Assert.Equal(1, _cacheDiagnostics.RebalanceExecutionCompleted); + } + + /// + /// Tests Invariant A.10 (🟢 Behavioral): User always receives data exactly corresponding to RequestedRange. + /// Verifies returned data matches requested range in length and content regardless of cache state. + /// This is a fundamental correctness guarantee. + /// + [Fact] + public async Task Invariant_A2_10_UserAlwaysReceivesExactRequestedRange() + { + // ARRANGE + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics)); + + // Act & Assert: Request various ranges and verify exact match + var testRanges = new[] + { + TestHelpers.CreateRange(100, 110), + TestHelpers.CreateRange(200, 250), + TestHelpers.CreateRange(105, 115), + TestHelpers.CreateRange(50, 60) + }; + + foreach (var range in testRanges) + { + var data = await cache.GetDataAsync(range, CancellationToken.None); + TestHelpers.AssertUserDataCorrect(data, range); + } + } + + #endregion + + #region A.3 Cache Mutation Rules (User Path) + + /// + /// Tests Invariant A.8 (🟢 Behavioral): User Path MUST NOT mutate cache under any circumstance. + /// Cache mutations (population, expansion, replacement) are performed exclusively by Rebalance Execution (single-writer). + /// + /// + /// Scenarios tested: + /// - ColdStart: Initial cache population during first request + /// - CacheExpansion: Intersecting request that partially overlaps existing cache + /// - FullReplacement: Non-intersecting jump to different region + /// In all cases, User Path returns correct data immediately but does NOT mutate cache. + /// Cache mutations occur asynchronously via Rebalance Execution. + /// + [Theory] + [InlineData("ColdStart", 100, 110, 0, 0, false)] // No prior request + [InlineData("CacheExpansion", 105, 120, 100, 110, true)] // Intersecting request + [InlineData("FullReplacement", 200, 210, 100, 110, true)] // Non-intersecting jump + public async Task Invariant_A3_8_UserPathNeverMutatesCache( + string _, int reqStart, int reqEnd, int priorStart, int priorEnd, bool hasPriorRequest) + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Execute prior request if needed to establish cache state + if (hasPriorRequest) + { + await TestHelpers.ExecuteRequestAndWaitForRebalance(cache, TestHelpers.CreateRange(priorStart, priorEnd)); + _cacheDiagnostics.Reset(); // Track only the test request + } + + // Execute the test request + var data = await cache.GetDataAsync(TestHelpers.CreateRange(reqStart, reqEnd), CancellationToken.None); + + // ASSERT: User receives correct data immediately + TestHelpers.AssertUserDataCorrect(data, TestHelpers.CreateRange(reqStart, reqEnd)); + + // User Path MUST NOT mutate cache (single-writer architecture) + TestHelpers.AssertNoUserPathMutations(_cacheDiagnostics); + + // Intent published for every request + TestHelpers.AssertIntentPublished(_cacheDiagnostics, 1); + + // Wait for rebalance and verify it completes (cache mutations happen here) + await cache.WaitForIdleAsync(); + TestHelpers.AssertRebalanceCompleted(_cacheDiagnostics); + } + + /// + /// Tests Invariant A.9a (🟢 Behavioral): Cache always represents a single contiguous range, never fragmented. + /// When non-intersecting requests arrive, cache replaces its contents entirely rather than maintaining + /// multiple disjoint ranges, ensuring efficient memory usage and predictable behavior. + /// + [Fact] + public async Task Invariant_A3_9a_CacheContiguityMaintained() + { + // ARRANGE + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics)); + + // ACT: Make various requests including overlapping and expanding ranges + var data1 = await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + var data2 = await cache.GetDataAsync(TestHelpers.CreateRange(105, 115), CancellationToken.None); + var data3 = await cache.GetDataAsync(TestHelpers.CreateRange(95, 120), CancellationToken.None); + + // ASSERT: All data is contiguous (no gaps) + TestHelpers.AssertUserDataCorrect(data1, TestHelpers.CreateRange(100, 110)); + TestHelpers.AssertUserDataCorrect(data2, TestHelpers.CreateRange(105, 115)); + TestHelpers.AssertUserDataCorrect(data3, TestHelpers.CreateRange(95, 120)); + } + + #endregion + + #endregion + + #region B. Cache State & Consistency Invariants + + /// + /// Tests Invariant B.11 (🟢 Behavioral): CacheData and CurrentCacheRange are always consistent. + /// At all observable points, cache's data content matches its declared range. Fundamental correctness invariant. + /// + [Fact] + public async Task Invariant_B11_CacheDataAndRangeAlwaysConsistent() + { + // ARRANGE + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics)); + + // Act & Assert: Make multiple requests and verify consistency + var ranges = new[] + { + TestHelpers.CreateRange(100, 110), + TestHelpers.CreateRange(105, 120), + TestHelpers.CreateRange(200, 250) + }; + + foreach (var range in ranges) + { + var data = await cache.GetDataAsync(range, CancellationToken.None); + var expectedLength = (int)range.End - (int)range.Start + 1; + Assert.Equal(expectedLength, data.Length); + TestHelpers.AssertUserDataCorrect(data, range); + } + } + + /// + /// Tests Invariant B.15 (🟢 Behavioral): Partially executed or cancelled Rebalance Execution + /// MUST NOT leave cache in inconsistent state. Verifies aggressive cancellation for user responsiveness + /// doesn't compromise correctness. Also validates F.35b (same guarantee from execution perspective). + /// + [Fact] + public async Task Invariant_B15_CancelledRebalanceDoesNotViolateConsistency() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromMilliseconds(100)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: First request starts rebalance intent, then immediately cancel with another request + await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + var data = await cache.GetDataAsync(TestHelpers.CreateRange(200, 210), CancellationToken.None); + + // ASSERT: Cache still returns correct data + TestHelpers.AssertUserDataCorrect(data, TestHelpers.CreateRange(200, 210)); + + // Verify cache is not corrupted by making another request + var data2 = await cache.GetDataAsync(TestHelpers.CreateRange(205, 215), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(data2, TestHelpers.CreateRange(205, 215)); + } + + #endregion + + #region C. Rebalance Intent & Temporal Invariants + + /// + /// Tests Invariant C.17 (🟢 Behavioral): At any point in time, at most one active rebalance intent exists. + /// Verifies rapid requests cause each new intent to cancel previous ones, preventing intent queue buildup. + /// + [Fact] + public async Task Invariant_C17_AtMostOneActiveIntent() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromMilliseconds(200)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Make rapid requests + await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + await cache.GetDataAsync(TestHelpers.CreateRange(110, 120), CancellationToken.None); + await cache.GetDataAsync(TestHelpers.CreateRange(120, 130), CancellationToken.None); + + // Wait for background rebalance to settle before checking counters + await cache.WaitForIdleAsync(); + + // ASSERT: Each new request publishes intent and cancels previous (at least 2 cancelled) + TestHelpers.AssertIntentPublished(_cacheDiagnostics, 3); + TestHelpers.AssertRebalancePathCancelled(_cacheDiagnostics, 2); + } + + /// + /// Tests Invariant C.18 (🟢 Behavioral): Any previously created rebalance intent is considered + /// obsolete after a new intent is generated. Prevents stale rebalance operations from executing + /// with outdated information. + /// + [Fact] + public async Task Invariant_C18_PreviousIntentBecomesObsolete() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromMilliseconds(150)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: First request publishes intent + await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + var publishedBefore = _cacheDiagnostics.RebalanceIntentPublished; + + // Second request publishes new intent and cancels old one + await cache.GetDataAsync(TestHelpers.CreateRange(200, 210), CancellationToken.None); + + // Wait for background rebalance to settle before checking counters + await cache.WaitForIdleAsync(); + + // ASSERT: New intent published, old one cancelled + Assert.True(_cacheDiagnostics.RebalanceIntentPublished > publishedBefore); + TestHelpers.AssertRebalancePathCancelled(_cacheDiagnostics); + } + + /// + /// Tests Invariant C.24 (🟡 Conceptual): Intent does not guarantee execution. Execution is opportunistic + /// and may be skipped due to: C.24a (request within NoRebalanceRange), C.24b (debounce), + /// C.24c (DesiredCacheRange equals CurrentCacheRange), C.24d (cancellation). + /// Demonstrates cache's opportunistic, efficiency-focused design. + /// + [Fact] + public async Task Invariant_C24_IntentDoesNotGuaranteeExecution() + { + // ARRANGE: Large threshold creates large NoRebalanceRange to block rebalance + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 2.0, rightCacheSize: 2.0, + leftThreshold: 0.5, rightThreshold: 0.5, debounceDelay: TimeSpan.FromMilliseconds(100)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: First request establishes cache + await TestHelpers.ExecuteRequestAndWaitForRebalance(cache, TestHelpers.CreateRange(100, 110)); + _cacheDiagnostics.Reset(); + + // Second request within NoRebalanceRange - intent published but execution may be skipped + await cache.GetDataAsync(TestHelpers.CreateRange(102, 108), CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ASSERT: Intent published but execution may be skipped due to NoRebalanceRange + TestHelpers.AssertIntentPublished(_cacheDiagnostics); + if (_cacheDiagnostics.RebalanceSkippedNoRebalanceRange > 0) + { + Assert.Equal(0, _cacheDiagnostics.RebalanceExecutionCompleted); + } + } + + /// + /// Tests Invariant C.23 (🟢 Behavioral): System stabilizes when user access patterns stabilize. + /// After initial burst, when access patterns stabilize (requests in same region), system converges + /// to stable state where subsequent requests are served from cache without triggering rebalance. + /// Demonstrates cache's convergence behavior. Related: C.22 (best-effort convergence guarantee). + /// + [Fact] + public async Task Invariant_C23_SystemStabilizesUnderLoad() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Rapid burst of requests + var tasks = new List(); + for (var i = 0; i < 10; i++) + { + var start = 100 + i * 2; + tasks.Add(cache.GetDataAsync(TestHelpers.CreateRange(start, start + 10), CancellationToken.None).AsTask()); + } + + await Task.WhenAll(tasks); + await cache.WaitForIdleAsync(); + + // ASSERT: System is stable and serves new requests correctly + var finalData = await cache.GetDataAsync(TestHelpers.CreateRange(105, 115), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(finalData, TestHelpers.CreateRange(105, 115)); + } + + #endregion + + #region D. Rebalance Decision Path Invariants + + /// + /// Tests Invariant D.27 (🟢 Behavioral): If RequestedRange is fully contained within NoRebalanceRange, + /// rebalance execution is prohibited. Verifies ThresholdRebalancePolicy prevents unnecessary rebalance + /// when requests fall within "dead zone" around current cache, reducing I/O and CPU usage. + /// Corresponds to sub-invariant C.24a (execution skipped due to policy). + /// + [Fact] + public async Task Invariant_D27_NoRebalanceIfRequestInNoRebalanceRange() + { + // ARRANGE: Large thresholds to create wide NoRebalanceRange + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 2.0, rightCacheSize: 2.0, + leftThreshold: 0.4, rightThreshold: 0.4, debounceDelay: TimeSpan.FromMilliseconds(1000)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: First request establishes cache and NoRebalanceRange + await TestHelpers.ExecuteRequestAndWaitForRebalance(cache, TestHelpers.CreateRange(100, 110)); + _cacheDiagnostics.Reset(); + + // Second request within NoRebalanceRange + await cache.GetDataAsync(TestHelpers.CreateRange(103, 107), CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ASSERT: Rebalance skipped due to NoRebalanceRange policy (execution should never start) + TestHelpers.AssertRebalanceSkippedDueToPolicy(_cacheDiagnostics); + } + + /// + /// Tests Invariant D.28 (🟢 Behavioral): If DesiredCacheRange == CurrentCacheRange, rebalance execution + /// not required. When cache already matches desired state, system skips execution as optimization. + /// Uses DEBUG counter RebalanceSkippedSameRange to verify early-exit in RebalanceExecutor. + /// Corresponds to sub-invariant C.24c (execution skipped due to optimization). + /// + [Fact] + public async Task Invariant_D28_SkipWhenDesiredEqualsCurrentRange() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 1.0, rightCacheSize: 1.0, + leftThreshold: 0.4, rightThreshold: 0.4, debounceDelay: TimeSpan.FromMilliseconds(100)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: First request establishes cache at desired range + var firstRange = TestHelpers.CreateRange(100, 110); + await TestHelpers.ExecuteRequestAndWaitForRebalance(cache, firstRange); + _cacheDiagnostics.Reset(); + + // Second request: same range should trigger intent, pass decision logic, starts executions, but skip before mutating data due to same-range optimization + await cache.GetDataAsync(firstRange, CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ASSERT: Intent published but execution optimized away + Assert.Equal(1, _cacheDiagnostics.RebalanceIntentPublished); + + // Execution should either be skipped entirely or not completed + // (skipped due to same-range optimization or never started) + Assert.Equal(0, _cacheDiagnostics.RebalanceExecutionCompleted); + Assert.Equal(1, _cacheDiagnostics.RebalanceSkippedSameRange); + } + + // NOTE: Invariant D.25, D.26, D.28, D.29: Decision Path is purely analytical, + // never mutates cache state, checks DesiredCacheRange == CurrentCacheRange + // Cannot be directly tested via public API - requires internal state access + // or integration tests with mock decision engine + + #endregion + + #region E. Cache Geometry & Policy Invariants + + /// + /// Tests Invariant E.30 (🟢 Behavioral): DesiredCacheRange is computed solely from RequestedRange + /// and cache configuration. Verifies ProportionalRangePlanner computes desired cache range deterministically + /// based only on user's requested range and config parameters (leftCacheSize, rightCacheSize), independent + /// of current cache contents. With config (leftSize=1.0, rightSize=1.0), cache expands by RequestedRange.Span + /// on each side. Related: E.31 (Architectural - DesiredCacheRange independent of current cache contents). + /// + [Fact] + public async Task Invariant_E30_DesiredRangeComputedFromConfigAndRequest() + { + // ARRANGE: Expansion coefficients: leftSize=1.0 (expand left by 100%), rightSize=1.0 (expand right by 100%) + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 1.0, rightCacheSize: 1.0, + debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Request a range [100, 110] (Size: 11) + var requestRange = TestHelpers.CreateRange(100, 110); + await TestHelpers.ExecuteRequestAndWaitForRebalance(cache, requestRange); + + // Calculate expected desired range using the helper that mimics ProportionalRangePlanner + var expectedDesiredRange = TestHelpers.CalculateExpectedDesiredRange(requestRange, options, _domain); + + // Reset counters to track only the next request + _cacheDiagnostics.Reset(); + + // Make another request within the calculated desired range + var withinDesired = await cache.GetDataAsync(TestHelpers.CreateRange(95, 115), CancellationToken.None); + + // ASSERT: Data is correct, demonstrating cache expanded based on configuration + TestHelpers.AssertUserDataCorrect(withinDesired, TestHelpers.CreateRange(95, 115)); + + // Verify this was a full cache hit, proving the desired range was calculated correctly + TestHelpers.AssertFullCacheHit(_cacheDiagnostics); + + // Verify the expected desired range calculation matches actual behavior + // The request [95, 115] should be fully within expectedDesiredRange + Assert.True(expectedDesiredRange.Contains(TestHelpers.CreateRange(95, 115)), + $"Request range [95, 115] should be within calculated desired range {expectedDesiredRange}"); + } + + // NOTE: Invariant E.31, E.32, E.33, E.34: DesiredCacheRange independent of current cache, + // represents canonical target state, geometry determined by configuration, + // NoRebalanceRange derived from CurrentCacheRange and config + // Cannot be directly observed via public API - requires internal state inspection + + /// + /// Demonstrates all three cache hit/miss scenarios tracked by instrumentation counters: + /// 1. Full Cache Miss (cold start and non-intersecting jump) + /// 2. Full Cache Hit (request fully within cache) + /// 3. Partial Cache Hit (request partially overlaps cache) + /// Validates cache hit/miss tracking is accurate for performance monitoring and testing. + /// Also verifies data source access patterns to ensure optimization correctness. + /// + [Fact] + public async Task CacheHitMiss_AllScenarios() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 1.0, rightCacheSize: 1.0, + debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // SCENARIO 1: Cold Start - Full Cache Miss + _cacheDiagnostics.Reset(); + var requestedRange = TestHelpers.CreateRange(100, 110); + await cache.GetDataAsync(requestedRange, CancellationToken.None); + TestHelpers.AssertFullCacheMiss(_cacheDiagnostics); + TestHelpers.AssertDataSourceFetchedFullRange(_cacheDiagnostics); + Assert.Equal(0, _cacheDiagnostics.UserRequestFullCacheHit); + Assert.Equal(0, _cacheDiagnostics.UserRequestPartialCacheHit); + Assert.Equal(0, _cacheDiagnostics.DataSourceFetchMissingSegments); + + // Wait for rebalance to populate cache with expanded range + await cache.WaitForIdleAsync(); + + // SCENARIO 2: Full Cache Hit - Request within cached range + _cacheDiagnostics.Reset(); + var expectedDesired = TestHelpers.CalculateExpectedDesiredRange(requestedRange, options, _domain); + await cache.GetDataAsync(expectedDesired, CancellationToken.None); + TestHelpers.AssertFullCacheHit(_cacheDiagnostics); + Assert.Equal(0, _cacheDiagnostics.UserRequestFullCacheMiss); + Assert.Equal(0, _cacheDiagnostics.UserRequestPartialCacheHit); + Assert.Equal(0, _cacheDiagnostics.DataSourceFetchSingleRange); + Assert.Equal(0, _cacheDiagnostics.DataSourceFetchMissingSegments); + + // Wait for rebalance + await cache.WaitForIdleAsync(); + + // SCENARIO 3: Partial Cache Hit - Request partially overlaps cache + _cacheDiagnostics.Reset(); + // Shift the expected desired range to create a new request that partially overlaps the existing cache + expectedDesired = TestHelpers.CalculateExpectedDesiredRange(expectedDesired, options, _domain); + expectedDesired = expectedDesired.Shift(_domain, expectedDesired.Span(_domain).Value / 2); + await cache.GetDataAsync(expectedDesired, CancellationToken.None); + TestHelpers.AssertPartialCacheHit(_cacheDiagnostics); + TestHelpers.AssertDataSourceFetchedMissingSegments(_cacheDiagnostics); + Assert.Equal(0, _cacheDiagnostics.UserRequestFullCacheMiss); + Assert.Equal(0, _cacheDiagnostics.UserRequestFullCacheHit); + Assert.Equal(0, _cacheDiagnostics.DataSourceFetchSingleRange); + + // Wait for rebalance + await cache.WaitForIdleAsync(); + + // SCENARIO 4: Full Cache Miss - Non-intersecting jump + _cacheDiagnostics.Reset(); + // Create a request that is completely outside the current cache range to trigger a full cache miss + expectedDesired = TestHelpers.CalculateExpectedDesiredRange(expectedDesired, options, _domain); + expectedDesired = expectedDesired.Shift(_domain, expectedDesired.Span(_domain).Value * 2); + await cache.GetDataAsync(expectedDesired, CancellationToken.None); + TestHelpers.AssertFullCacheMiss(_cacheDiagnostics); + TestHelpers.AssertDataSourceFetchedFullRange(_cacheDiagnostics); + Assert.Equal(0, _cacheDiagnostics.UserRequestFullCacheHit); + Assert.Equal(0, _cacheDiagnostics.UserRequestPartialCacheHit); + Assert.Equal(0, _cacheDiagnostics.DataSourceFetchMissingSegments); + } + + #endregion + + #region F. Rebalance Execution Invariants + + /// + /// Tests Invariants F.35 (🟢 Behavioral), F.35a (🔵 Architectural), and G.46 (🟢 Behavioral): + /// Rebalance Execution MUST support cancellation at all stages and yield to User Path immediately. + /// Validates detailed cancellation mechanics, lifecycle tracking (Started == Completed + Cancelled), + /// and high-level guarantee that cancellation works in all scenarios. + /// Uses slow data source to allow cancellation during execution. Verifies DEBUG instrumentation counters + /// ensure proper lifecycle tracking. Related: A.0a (User Path cancels rebalance), C.24d (execution + /// skipped due to cancellation). + /// + [Fact] + public async Task Invariant_F35_G46_RebalanceCancellationBehavior() + { + // ARRANGE: Slow data source to allow cancellation during execution + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 2.0, rightCacheSize: 2.0, + debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options, + fetchDelay: TimeSpan.FromMilliseconds(200))); + + // ACT: First request triggers rebalance, then immediately cancel with multiple new requests + await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + await cache.GetDataAsync(TestHelpers.CreateRange(105, 115), CancellationToken.None); + await cache.GetDataAsync(TestHelpers.CreateRange(110, 120), CancellationToken.None); + await cache.WaitForIdleAsync(); + + // ASSERT: Verify cancellation occurred (F.35, G.46) + TestHelpers.AssertRebalancePathCancelled(_cacheDiagnostics, 2); // 2 cancels for the 2 new requests after the first + + // Verify Rebalance lifecycle integrity: every started execution reaches terminal state (F.35a) + TestHelpers.AssertRebalanceLifecycleIntegrity(_cacheDiagnostics); + } + + /// + /// Tests Invariant F.36 (🔵 Architectural) and F.36a (🟢 Behavioral): Rebalance Execution Path is the + /// only path responsible for cache normalization (expanding, trimming, recomputing NoRebalanceRange). + /// After rebalance completes, cache is normalized to serve data from expanded range beyond original request. + /// User Path performs minimal mutations while Rebalance Execution handles optimization. + /// + [Fact] + public async Task Invariant_F36a_RebalanceNormalizesCache() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 1.0, rightCacheSize: 1.0, + debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Make request and wait for rebalance + await TestHelpers.ExecuteRequestAndWaitForRebalance(cache, TestHelpers.CreateRange(100, 110)); + + // ASSERT: Rebalance executed successfully + TestHelpers.AssertRebalanceCompleted(_cacheDiagnostics); + TestHelpers.AssertRebalanceLifecycleIntegrity(_cacheDiagnostics); + + // Cache should be normalized - verify by requesting from expected expanded range + var extendedData = await cache.GetDataAsync(TestHelpers.CreateRange(95, 115), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(extendedData, TestHelpers.CreateRange(95, 115)); + } + + /// + /// Tests Invariants F.40, F.41, F.42 (🟢 Behavioral/🟡 Conceptual): Post-execution guarantees. + /// F.40: CacheData corresponds to DesiredCacheRange. F.41: CurrentCacheRange == DesiredCacheRange. + /// F.42: NoRebalanceRange is recomputed. After successful rebalance, cache reaches normalized state + /// serving data from expanded/optimized range (based on config with leftSize=1.0, rightSize=1.0). + /// + [Fact] + public async Task Invariant_F40_F41_F42_PostExecutionGuarantees() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 1.0, rightCacheSize: 1.0, + debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Request and wait for rebalance to complete + await TestHelpers.ExecuteRequestAndWaitForRebalance(cache, TestHelpers.CreateRange(100, 110)); + + if (_cacheDiagnostics.RebalanceExecutionCompleted > 0) + { + // After rebalance, cache should serve data from normalized range [100-11, 110+11] = [89, 121] + var normalizedData = await cache.GetDataAsync(TestHelpers.CreateRange(90, 120), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(normalizedData, TestHelpers.CreateRange(90, 120)); + } + } + + // NOTE: Invariant F.38, F.39: Requests data from IDataSource only for missing subranges, + // does not overwrite existing data + // Requires instrumentation of CacheDataExtensionService or mock data source tracking + + #endregion + + #region G. Execution Context & Scheduling Invariants + + /// + /// Tests Invariants G.43, G.44, G.45: Execution context separation between User Path and Rebalance operations. + /// G.43: User Path operates in user execution context (request completes quickly). + /// G.44: Rebalance Decision/Execution Path execute outside user context (Task.Run). + /// G.45: Rebalance Execution performs I/O only in background context (not blocking user). + /// Verifies user requests complete quickly without blocking on background operations, proving rebalance + /// work is properly scheduled on background threads. Critical for maintaining responsive user-facing latency. + /// + [Fact] + public async Task Invariant_G43_G44_G45_ExecutionContextSeparation() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromMilliseconds(100)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: User request completes synchronously (in user context) + var stopwatch = System.Diagnostics.Stopwatch.StartNew(); + var data = await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + stopwatch.Stop(); + + // ASSERT: User request completed quickly (didn't wait for background rebalance) + Assert.Equal(1, _cacheDiagnostics.UserRequestServed); + Assert.Equal(1, _cacheDiagnostics.RebalanceIntentPublished); + Assert.Equal(0, _cacheDiagnostics.RebalanceExecutionCompleted); + TestHelpers.AssertUserDataCorrect(data, TestHelpers.CreateRange(100, 110)); + await cache.WaitForIdleAsync(); + Assert.Equal(1, _cacheDiagnostics.RebalanceExecutionCompleted); + } + + /// + /// Tests Invariant G.46 (🟢 Behavioral): User-facing cancellation during IDataSource fetch operations. + /// Verifies User Path properly propagates cancellation token through to IDataSource.FetchAsync(). + /// Users can cancel their own requests during potentially long-running data source operations. + /// Related: G.46 covers "all scenarios" - this test focuses on user-facing cancellation. + /// See also: Invariant_F35_G46 for background rebalance cancellation. + /// + [Fact] + public async Task Invariant_G46_UserCancellationDuringFetch() + { + // ARRANGE: Slow mock data source to allow cancellation during fetch + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, TestHelpers.CreateDefaultOptions(), + fetchDelay: TimeSpan.FromMilliseconds(300))); + + // Act & Assert: Cancel token during fetch operation + var cts = new CancellationTokenSource(); + var requestTask = cache.GetDataAsync(TestHelpers.CreateRange(100, 110), cts.Token).AsTask(); + + // Cancel while fetch is in progress + await Task.Delay(50, CancellationToken.None); + await cts.CancelAsync(); + + // Should throw OperationCanceledException or derived type (TaskCanceledException) + var exception = await Record.ExceptionAsync(async () => await requestTask); + Assert.True(exception is OperationCanceledException, + $"Expected OperationCanceledException but got {exception.GetType().Name}"); + } + + #endregion + + #region Additional Comprehensive Tests + + /// + /// Comprehensive integration test covering multiple invariants in realistic usage scenario. + /// Tests: Cold start (A.8), Cache expansion (A.8), Background rebalance normalization (F.36a), + /// Non-intersecting replacement (A.8, A.9a), Cache consistency (B.11). + /// Validates all components work correctly together. Verifies: user requests always served (A.1), + /// data is correct (A.10), cache properly maintains state through multiple transitions. + /// + [Fact] + public async Task CompleteScenario_MultipleRequestsWithRebalancing() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(leftCacheSize: 1.0, rightCacheSize: 1.0, + leftThreshold: 0.2, rightThreshold: 0.2, debounceDelay: TimeSpan.FromMilliseconds(50)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // Act & Assert: Sequential user requests + // Request 1: Cold start + var data1 = await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(data1, TestHelpers.CreateRange(100, 110)); + + // Request 2: Overlapping expansion + var data2 = await cache.GetDataAsync(TestHelpers.CreateRange(105, 120), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(data2, TestHelpers.CreateRange(105, 120)); + await cache.WaitForIdleAsync(); + + // Request 3: Within cached/rebalanced range + var data3 = await cache.GetDataAsync(TestHelpers.CreateRange(110, 115), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(data3, TestHelpers.CreateRange(110, 115)); + + // Request 4: Non-intersecting jump + var data4 = await cache.GetDataAsync(TestHelpers.CreateRange(200, 210), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(data4, TestHelpers.CreateRange(200, 210)); + await cache.WaitForIdleAsync(); + + // Request 5: Verify cache stability + var data5 = await cache.GetDataAsync(TestHelpers.CreateRange(205, 215), CancellationToken.None); + TestHelpers.AssertUserDataCorrect(data5, TestHelpers.CreateRange(205, 215)); + + // Wait for background rebalance to settle before checking counters + await cache.WaitForIdleAsync(); + + // Verify key behavioral properties + Assert.Equal(5, _cacheDiagnostics.UserRequestServed); + Assert.True(_cacheDiagnostics.RebalanceIntentPublished >= 5); + TestHelpers.AssertRebalanceCompleted(_cacheDiagnostics); + } + + /// + /// Comprehensive concurrency test with rapid burst of 20 concurrent requests verifying intent cancellation + /// and system stability under high load. Validates: All requests served correctly (A.1, A.10), + /// Intent cancellation works (C.17, C.18), At most one active intent (C.17), + /// Cache remains consistent (B.11, B.15). Ensures single-consumer model with cancellation-based + /// coordination handles realistic high-load scenarios without data corruption or request failures. + /// + [Fact] + public async Task ConcurrencyScenario_RapidRequestsBurstWithCancellation() + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(debounceDelay: TimeSpan.FromSeconds(1)); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // ACT: Fire 20 rapid concurrent requests + var tasks = new List>>(); + for (var i = 0; i < 20; i++) + { + var start = 100 + i * 5; + tasks.Add(cache.GetDataAsync(TestHelpers.CreateRange(start, start + 10), CancellationToken.None).AsTask()); + } + + var results = await Task.WhenAll(tasks); + + // Wait for background rebalance to settle before checking counters + await cache.WaitForIdleAsync(); + + // ASSERT: All requests completed successfully with correct data + Assert.Equal(20, results.Length); + for (var i = 0; i < results.Length; i++) + { + var expectedRange = TestHelpers.CreateRange(100 + i * 5, 110 + i * 5); + TestHelpers.AssertUserDataCorrect(results[i], expectedRange); + } + + Assert.Equal(20, _cacheDiagnostics.UserRequestServed); + Assert.True(_cacheDiagnostics.RebalanceIntentPublished == 20); + TestHelpers.AssertRebalancePathCancelled(_cacheDiagnostics, 19); // Each new request cancels the previous intent, so expect 19 cancellations + Assert.Equal(1, _cacheDiagnostics.RebalanceExecutionCompleted); + } + + /// + /// Tests read mode behavior. Snapshot mode: zero-allocation reads via direct ReadOnlyMemory access. + /// CopyOnRead mode: defensive copies for memory safety when callers hold references beyond the call. + /// Both modes return correct data matching requested ranges. + /// + [Theory] + [InlineData(UserCacheReadMode.Snapshot)] + [InlineData(UserCacheReadMode.CopyOnRead)] + public async Task ReadMode_VerifyBehavior(UserCacheReadMode readMode) + { + // ARRANGE + var options = TestHelpers.CreateDefaultOptions(readMode: readMode); + var (cache, _) = TrackCache(TestHelpers.CreateCacheWithDefaults(_domain, _cacheDiagnostics, options)); + + // Act + var data1 = await cache.GetDataAsync(TestHelpers.CreateRange(100, 110), CancellationToken.None); + var data2 = await cache.GetDataAsync(TestHelpers.CreateRange(105, 115), CancellationToken.None); + + // Assert + TestHelpers.VerifyDataMatchesRange(data1, TestHelpers.CreateRange(100, 110)); + TestHelpers.VerifyDataMatchesRange(data2, TestHelpers.CreateRange(105, 115)); + } + + #endregion +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Extensions/IntegerVariableStepDomain.cs b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Extensions/IntegerVariableStepDomain.cs new file mode 100644 index 0000000..3be4d2b --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Extensions/IntegerVariableStepDomain.cs @@ -0,0 +1,132 @@ +using Intervals.NET.Domain.Abstractions; + +namespace SlidingWindowCache.Unit.Tests.Infrastructure.Extensions; + +/// +/// Test implementation of IVariableStepDomain for integer values with custom step sizes. +/// Used for testing domain-agnostic extension methods with variable-step domains. +/// +internal class IntegerVariableStepDomain : IVariableStepDomain +{ + private readonly int[] _steps; + + public IntegerVariableStepDomain(int[] steps) + { + if (steps == null || steps.Length == 0) + throw new ArgumentException("Steps array cannot be null or empty.", nameof(steps)); + + // Ensure steps are sorted + _steps = steps.OrderBy(s => s).ToArray(); + } + + public IComparer Comparer => Comparer.Default; + + public int? GetPreviousStep(int value) + { + for (var i = _steps.Length - 1; i >= 0; i--) + { + if (Comparer.Compare(_steps[i], value) < 0) + { + return _steps[i]; + } + } + return null; + } + + public int? GetNextStep(int value) + { + foreach (var step in _steps) + { + if (Comparer.Compare(step, value) > 0) + { + return step; + } + } + return null; + } + + // IRangeDomain base interface methods + public int Add(int value, long steps) + { + if (steps == 0) return value; + + var current = value; + if (steps > 0) + { + for (long i = 0; i < steps; i++) + { + var next = GetNextStep(current); + if (next == null) + throw new InvalidOperationException($"Cannot add {steps} steps from {value}: no more steps available"); + current = next.Value; + } + } + else + { + for (long i = 0; i < -steps; i++) + { + var prev = GetPreviousStep(current); + if (prev == null) + throw new InvalidOperationException($"Cannot subtract {-steps} steps from {value}: no more steps available"); + current = prev.Value; + } + } + return current; + } + + public int Subtract(int value, long steps) + { + return Add(value, -steps); + } + + public int Floor(int value) + { + // Find the largest step <= value + for (var i = _steps.Length - 1; i >= 0; i--) + { + if (Comparer.Compare(_steps[i], value) <= 0) + { + return _steps[i]; + } + } + // If no step is <= value, return the first step + return _steps[0]; + } + + public int Ceiling(int value) + { + // Find the smallest step >= value + foreach (var step in _steps) + { + if (Comparer.Compare(step, value) >= 0) + { + return step; + } + } + // If no step is >= value, return the last step + return _steps[^1]; + } + + public long Distance(int from, int to) + { + var comparison = Comparer.Compare(from, to); + if (comparison == 0) return 0; + + var start = comparison < 0 ? from : to; + var end = comparison < 0 ? to : from; + + long count = 0; + var current = start; + + while (Comparer.Compare(current, end) < 0) + { + var next = GetNextStep(current); + if (next == null) + break; + current = next.Value; + count++; + } + + return comparison < 0 ? count : -count; + } +} diff --git a/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Extensions/IntervalsNetDomainExtensionsTests.cs b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Extensions/IntervalsNetDomainExtensionsTests.cs new file mode 100644 index 0000000..98d8fb9 --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Extensions/IntervalsNetDomainExtensionsTests.cs @@ -0,0 +1,427 @@ +using Intervals.NET.Domain.Abstractions; +using Intervals.NET.Domain.Default.Numeric; +using Moq; +using SlidingWindowCache.Infrastructure.Extensions; + +namespace SlidingWindowCache.Unit.Tests.Infrastructure.Extensions; + +/// +/// Unit tests for IntervalsNetDomainExtensions that verify domain-agnostic extension methods +/// work correctly with both fixed-step and variable-step domains. +/// +public class IntervalsNetDomainExtensionsTests +{ + #region Span Method Tests + + [Fact] + public void Span_WithFixedStepDomain_ReturnsCorrectStepCount() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var span = range.Span(domain); + + // ASSERT + Assert.Equal(11, span.Value); // [10, 20] inclusive = 11 steps + Assert.True(span.IsFinite); + } + + [Fact] + public void Span_WithFixedStepDomain_SinglePoint_ReturnsOne() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(5, 5); + + // ACT + var span = range.Span(domain); + + // ASSERT + Assert.Equal(1, span.Value); // Single point = 1 step + Assert.True(span.IsFinite); + } + + [Fact] + public void Span_WithFixedStepDomain_LargeRange_ReturnsCorrectCount() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(0, 100); + + // ACT + var span = range.Span(domain); + + // ASSERT + Assert.Equal(101, span.Value); // [0, 100] inclusive = 101 steps + Assert.True(span.IsFinite); + } + + [Fact] + public void Span_WithVariableStepDomain_ReturnsCorrectStepCount() + { + // ARRANGE - Create a variable-step domain with custom steps + var steps = new[] { 1, 2, 5, 10, 20, 50 }; + var domain = new IntegerVariableStepDomain(steps); + var range = Intervals.NET.Factories.Range.Closed(1, 20); + + // ACT + var span = range.Span(domain); + + // ASSERT + Assert.Equal(5, span.Value); // Steps: 1, 2, 5, 10, 20 = 5 steps + Assert.True(span.IsFinite); + } + + [Fact] + public void Span_WithVariableStepDomain_PartialRange_ReturnsCorrectStepCount() + { + // ARRANGE + var steps = new[] { 1, 2, 5, 10, 20, 50, 100 }; + var domain = new IntegerVariableStepDomain(steps); + var range = Intervals.NET.Factories.Range.Closed(5, 50); + + // ACT + var span = range.Span(domain); + + // ASSERT + Assert.Equal(4, span.Value); // Steps: 5, 10, 20, 50 = 4 steps + Assert.True(span.IsFinite); + } + + [Fact] + public void Span_WithUnsupportedDomain_ThrowsNotSupportedException() + { + // ARRANGE - Create a mock domain that doesn't implement either interface + var mockDomain = new Mock>(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT & ASSERT + var exception = Assert.Throws(() => range.Span(mockDomain.Object)); + Assert.Contains("must implement either IFixedStepDomain or IVariableStepDomain", exception.Message); + } + + #endregion + + #region Expand Method Tests + + [Fact] + public void Expand_WithFixedStepDomain_ExpandsBothSides() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var expanded = range.Expand(domain, left: 5, right: 3); + + // ASSERT + Assert.Equal(5, expanded.Start.Value); // 10 - 5 = 5 + Assert.Equal(23, expanded.End.Value); // 20 + 3 = 23 + } + + [Fact] + public void Expand_WithFixedStepDomain_ZeroExpansion_ReturnsSameRange() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var expanded = range.Expand(domain, left: 0, right: 0); + + // ASSERT + Assert.Equal(10, expanded.Start.Value); + Assert.Equal(20, expanded.End.Value); + } + + [Fact] + public void Expand_WithFixedStepDomain_NegativeExpansion_Shrinks() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 30); + + // ACT + var shrunk = range.Expand(domain, left: -2, right: -3); + + // ASSERT + Assert.Equal(12, shrunk.Start.Value); // 10 + 2 = 12 + Assert.Equal(27, shrunk.End.Value); // 30 - 3 = 27 + } + + [Fact] + public void Expand_WithFixedStepDomain_OnlyLeft_ExpandsLeftSide() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var expanded = range.Expand(domain, left: 5, right: 0); + + // ASSERT + Assert.Equal(5, expanded.Start.Value); + Assert.Equal(20, expanded.End.Value); + } + + [Fact] + public void Expand_WithFixedStepDomain_OnlyRight_ExpandsRightSide() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var expanded = range.Expand(domain, left: 0, right: 5); + + // ASSERT + Assert.Equal(10, expanded.Start.Value); + Assert.Equal(25, expanded.End.Value); + } + + [Fact] + public void Expand_WithVariableStepDomain_ExpandsCorrectly() + { + // ARRANGE - Create a variable-step domain with custom steps + var steps = new[] { 1, 2, 5, 10, 20, 50, 100 }; + var domain = new IntegerVariableStepDomain(steps); + var range = Intervals.NET.Factories.Range.Closed(5, 20); + + // ACT - Expand by 1 step on each side + var expanded = range.Expand(domain, left: 1, right: 1); + + // ASSERT + // Left: 5 - 1 step = 2, Right: 20 + 1 step = 50 + Assert.Equal(2, expanded.Start.Value); + Assert.Equal(50, expanded.End.Value); + } + + [Fact] + public void Expand_WithVariableStepDomain_MultipleSteps_ExpandsCorrectly() + { + // ARRANGE + var steps = new[] { 1, 5, 10, 20, 50, 100 }; + var domain = new IntegerVariableStepDomain(steps); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT - Expand by 2 steps on left, 1 step on right + var expanded = range.Expand(domain, left: 2, right: 1); + + // ASSERT + // Left: 10 - 2 steps = 1, Right: 20 + 1 step = 50 + Assert.Equal(1, expanded.Start.Value); + Assert.Equal(50, expanded.End.Value); + } + + [Fact] + public void Expand_WithUnsupportedDomain_ThrowsNotSupportedException() + { + // ARRANGE - Create a mock domain that doesn't implement either interface + var mockDomain = new Mock>(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT & ASSERT + var exception = Assert.Throws(() => + range.Expand(mockDomain.Object, left: 5, right: 5)); + Assert.Contains("must implement either IFixedStepDomain or IVariableStepDomain", exception.Message); + } + + #endregion + + #region ExpandByRatio Method Tests + + [Fact] + public void ExpandByRatio_WithFixedStepDomain_ExpandsBothSides() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); // Span = 11 steps + + // ACT - Expand by 50% on each side + var expanded = range.ExpandByRatio(domain, leftRatio: 0.5, rightRatio: 0.5); + + // ASSERT + // Span = 11, so 50% = 5.5 steps (rounds to 5 or 6 depending on implementation) + // Left: 10 - ~5 = ~5, Right: 20 + ~5 = ~25 + Assert.True(expanded.Start.Value <= 5); + Assert.True(expanded.End.Value >= 25); + Assert.True(expanded.Start.Value < 10); + Assert.True(expanded.End.Value > 20); + } + + [Fact] + public void ExpandByRatio_WithFixedStepDomain_ZeroRatio_ReturnsSameRange() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var expanded = range.ExpandByRatio(domain, leftRatio: 0.0, rightRatio: 0.0); + + // ASSERT + Assert.Equal(10, expanded.Start.Value); + Assert.Equal(20, expanded.End.Value); + } + + [Fact] + public void ExpandByRatio_WithFixedStepDomain_NegativeRatio_Shrinks() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 30); // Span = 21 steps + + // ACT - Shrink by 20% on each side (negative ratio) + var shrunk = range.ExpandByRatio(domain, leftRatio: -0.2, rightRatio: -0.2); + + // ASSERT + // 20% of 21 = 4.2 steps (rounds to 4) + // The range should be smaller + Assert.True(shrunk.Start.Value >= 10); + Assert.True(shrunk.End.Value <= 30); + Assert.True(shrunk.Start.Value > 10 || shrunk.End.Value < 30); // At least one side changed + } + + [Fact] + public void ExpandByRatio_WithFixedStepDomain_OnlyLeftRatio_ExpandsLeftSide() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var expanded = range.ExpandByRatio(domain, leftRatio: 1.0, rightRatio: 0.0); + + // ASSERT + // Left expands by 100% of span (11 steps) + Assert.True(expanded.Start.Value < 10); + Assert.Equal(20, expanded.End.Value); + } + + [Fact] + public void ExpandByRatio_WithFixedStepDomain_OnlyRightRatio_ExpandsRightSide() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var expanded = range.ExpandByRatio(domain, leftRatio: 0.0, rightRatio: 1.0); + + // ASSERT + // Right expands by 100% of span (11 steps) + Assert.Equal(10, expanded.Start.Value); + Assert.True(expanded.End.Value > 20); + } + + [Fact] + public void ExpandByRatio_WithFixedStepDomain_LargeRatio_ExpandsSignificantly() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(100, 110); // Span = 11 steps + + // ACT - Expand by 200% on each side + var expanded = range.ExpandByRatio(domain, leftRatio: 2.0, rightRatio: 2.0); + + // ASSERT + // 200% of 11 = 22 steps + // The expansion should be substantial + Assert.True(expanded.Start.Value < 100); + Assert.True(expanded.End.Value > 110); + Assert.True((100 - expanded.Start.Value) >= 20); // At least 20 steps left + Assert.True((expanded.End.Value - 110) >= 20); // At least 20 steps right + } + + [Fact] + public void ExpandByRatio_WithVariableStepDomain_ExpandsCorrectly() + { + // ARRANGE + var steps = new[] { 1, 2, 5, 10, 15, 20, 25, 30, 40, 50, 100, 200 }; + var domain = new IntegerVariableStepDomain(steps); + var range = Intervals.NET.Factories.Range.Closed(10, 30); // Span = 4 steps (10, 15, 20, 25, 30) + + // ACT - Expand by 50% on each side (2 steps on each side) + var expanded = range.ExpandByRatio(domain, leftRatio: 0.5, rightRatio: 0.5); + + // ASSERT + // Original range covers steps: 10, 15, 20, 25, 30 (5 steps) + // Expanding by 50% should add ~2-3 steps on each side + Assert.True(expanded.Start.Value < 10); + Assert.True(expanded.End.Value > 30); + } + + [Fact] + public void ExpandByRatio_WithUnsupportedDomain_ThrowsNotSupportedException() + { + // ARRANGE - Create a mock domain that doesn't implement either interface + var mockDomain = new Mock>(); + var range = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT & ASSERT + var exception = Assert.Throws(() => + range.ExpandByRatio(mockDomain.Object, leftRatio: 0.5, rightRatio: 0.5)); + Assert.Contains("must implement either IFixedStepDomain or IVariableStepDomain", exception.Message); + } + + #endregion + + #region Integration Tests - Multiple Operations + + [Fact] + public void MultipleOperations_Span_Then_Expand_WorksTogether() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var originalRange = Intervals.NET.Factories.Range.Closed(10, 20); + + // ACT + var originalSpan = originalRange.Span(domain); + var expanded = originalRange.Expand(domain, left: 5, right: 5); + var expandedSpan = expanded.Span(domain); + + // ASSERT + Assert.Equal(11, originalSpan.Value); // Original: [10, 20] = 11 steps + Assert.Equal(21, expandedSpan.Value); // Expanded: [5, 25] = 21 steps + Assert.Equal(originalSpan.Value + 10, expandedSpan.Value); // Added 5 steps on each side + } + + [Fact] + public void MultipleOperations_ExpandByRatio_Then_Span_WorksTogether() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(100, 110); // Span = 11 steps + + // ACT + var expanded = range.ExpandByRatio(domain, leftRatio: 1.0, rightRatio: 1.0); + var expandedSpan = expanded.Span(domain); + + // ASSERT + // Expanding by 100% on each side should roughly triple the span + Assert.True(expandedSpan.Value > 11); // Must be larger + Assert.True(expandedSpan.Value >= 30); // Should be approximately 33 (11 + 11 + 11) + } + + [Fact] + public void MultipleOperations_ChainedExpansions_WorkCorrectly() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var range = Intervals.NET.Factories.Range.Closed(50, 60); // Span = 11 steps + + // ACT - Chain multiple expansions + var firstExpansion = range.Expand(domain, left: 2, right: 2); + var secondExpansion = firstExpansion.Expand(domain, left: 3, right: 3); + + // ASSERT + Assert.Equal(48, firstExpansion.Start.Value); // 50 - 2 = 48 + Assert.Equal(62, firstExpansion.End.Value); // 60 + 2 = 62 + Assert.Equal(45, secondExpansion.Start.Value); // 48 - 3 = 45 + Assert.Equal(65, secondExpansion.End.Value); // 62 + 3 = 65 + } + + #endregion +} diff --git a/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Instrumentation/NoOpDiagnosticsTests.cs b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Instrumentation/NoOpDiagnosticsTests.cs new file mode 100644 index 0000000..7e2a7fc --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Instrumentation/NoOpDiagnosticsTests.cs @@ -0,0 +1,41 @@ +using SlidingWindowCache.Infrastructure.Instrumentation; + +namespace SlidingWindowCache.Unit.Tests.Infrastructure.Instrumentation; + +/// +/// Unit tests for NoOpDiagnostics to ensure it never throws exceptions. +/// This is critical because diagnostic failures should never break cache functionality. +/// +public class NoOpDiagnosticsTests +{ + [Fact] + public void AllMethods_WhenCalled_DoNotThrowExceptions() + { + // ARRANGE + var diagnostics = new NoOpDiagnostics(); + var testException = new InvalidOperationException("Test exception"); + + // ACT & ASSERT - Call all methods and verify none throw exceptions + var exception = Record.Exception(() => + { + diagnostics.CacheExpanded(); + diagnostics.CacheReplaced(); + diagnostics.DataSourceFetchMissingSegments(); + diagnostics.DataSourceFetchSingleRange(); + diagnostics.RebalanceExecutionCancelled(); + diagnostics.RebalanceExecutionCompleted(); + diagnostics.RebalanceExecutionStarted(); + diagnostics.RebalanceIntentCancelled(); + diagnostics.RebalanceIntentPublished(); + diagnostics.RebalanceSkippedNoRebalanceRange(); + diagnostics.RebalanceSkippedSameRange(); + diagnostics.RebalanceExecutionFailed(testException); + diagnostics.UserRequestFullCacheHit(); + diagnostics.UserRequestFullCacheMiss(); + diagnostics.UserRequestPartialCacheHit(); + diagnostics.UserRequestServed(); + }); + + Assert.Null(exception); + } +} diff --git a/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/CopyOnReadStorageTests.cs b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/CopyOnReadStorageTests.cs new file mode 100644 index 0000000..33befb6 --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/CopyOnReadStorageTests.cs @@ -0,0 +1,552 @@ +using Intervals.NET.Data.Extensions; +using Intervals.NET.Domain.Default.Numeric; +using SlidingWindowCache.Infrastructure.Storage; +using SlidingWindowCache.Public.Configuration; +using SlidingWindowCache.Unit.Tests.Infrastructure.Extensions; +using static SlidingWindowCache.Unit.Tests.Infrastructure.Storage.TestInfrastructure.StorageTestHelpers; + +namespace SlidingWindowCache.Unit.Tests.Infrastructure.Storage; + +/// +/// Unit tests for CopyOnReadStorage that verify the ICacheStorage interface contract, +/// data correctness (Invariant B.11), dual-buffer staging pattern, and error handling. +/// +public class CopyOnReadStorageTests +{ + #region Interface Contract Tests + + [Fact] + public void Mode_ReturnsCopyOnRead() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + // ACT + var mode = storage.Mode; + + // ASSERT + Assert.Equal(UserCacheReadMode.CopyOnRead, mode); + } + + [Fact] + public void Range_InitiallyEmpty() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + // ACT & ASSERT + // Default Range behavior - storage starts uninitialized + // Range is a value type, so it's always non-null + _ = storage.Range; + } + + [Fact] + public void Range_UpdatesAfterRematerialize() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + var rangeData = CreateRangeData(10, 20, domain); + + // ACT + storage.Rematerialize(rangeData); + + // ASSERT + Assert.Equal(10, storage.Range.Start.Value); + Assert.Equal(20, storage.Range.End.Value); + } + + #endregion + + #region Rematerialize Tests + + [Fact] + public void Rematerialize_StoresDataCorrectly() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + var rangeData = CreateRangeData(5, 15, domain); + + // ACT + storage.Rematerialize(rangeData); + var result = storage.Read(CreateRange(5, 15)); + + // ASSERT + VerifyDataMatchesRange(result, 5, 15); + } + + [Fact] + public void Rematerialize_UpdatesRange() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + var rangeData = CreateRangeData(100, 200, domain); + + // ACT + storage.Rematerialize(rangeData); + + // ASSERT + Assert.Equal(100, storage.Range.Start.Value); + Assert.Equal(200, storage.Range.End.Value); + } + + [Fact] + public void Rematerialize_MultipleCalls_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + // First rematerialization + var firstData = CreateRangeData(0, 10, domain); + storage.Rematerialize(firstData); + + // ACT - Second rematerialization with different range + var secondData = CreateRangeData(20, 30, domain); + storage.Rematerialize(secondData); + var result = storage.Read(CreateRange(20, 30)); + + // ASSERT + Assert.Equal(20, storage.Range.Start.Value); + Assert.Equal(30, storage.Range.End.Value); + VerifyDataMatchesRange(result, 20, 30); + } + + [Fact] + public void Rematerialize_WithSameSize_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 10, domain)); + + // ACT - Same size, different values + storage.Rematerialize(CreateRangeData(100, 110, domain)); + var result = storage.Read(CreateRange(100, 110)); + + // ASSERT + VerifyDataMatchesRange(result, 100, 110); + } + + [Fact] + public void Rematerialize_WithLargerSize_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 5, domain)); + + // ACT - Larger size + storage.Rematerialize(CreateRangeData(0, 20, domain)); + var result = storage.Read(CreateRange(0, 20)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 20); + } + + [Fact] + public void Rematerialize_WithSmallerSize_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT - Smaller size + storage.Rematerialize(CreateRangeData(0, 5, domain)); + var result = storage.Read(CreateRange(0, 5)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 5); + } + + [Fact] + public void Rematerialize_SequentialCalls_MaintainsCorrectness() + { + // ARRANGE - Test dual-buffer staging pattern with sequential rematerializations + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + // ACT & ASSERT - Each rematerialization should work correctly + for (var i = 0; i < 5; i++) + { + var start = i * 10; + var end = start + 10; + storage.Rematerialize(CreateRangeData(start, end, domain)); + + var result = storage.Read(CreateRange(start, end)); + VerifyDataMatchesRange(result, start, end); + } + } + + #endregion + + #region Read Tests + + [Fact] + public void Read_FullRange_ReturnsAllData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 10, domain)); + + // ACT + var result = storage.Read(CreateRange(0, 10)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 10); + } + + [Fact] + public void Read_PartialRange_AtStart_ReturnsCorrectSubset() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT + var result = storage.Read(CreateRange(0, 5)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 5); + } + + [Fact] + public void Read_PartialRange_InMiddle_ReturnsCorrectSubset() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT + var result = storage.Read(CreateRange(5, 15)); + + // ASSERT + VerifyDataMatchesRange(result, 5, 15); + } + + [Fact] + public void Read_PartialRange_AtEnd_ReturnsCorrectSubset() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT + var result = storage.Read(CreateRange(15, 20)); + + // ASSERT + VerifyDataMatchesRange(result, 15, 20); + } + + [Fact] + public void Read_SingleElement_ReturnsOneValue() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 10, domain)); + + // ACT + var result = storage.Read(CreateRange(5, 5)); + + // ASSERT + Assert.Equal(1, result.Length); + Assert.Equal(5, result.Span[0]); + } + + [Fact] + public void Read_AtExactBoundaries_ReturnsCorrectData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(10, 20, domain)); + + // ACT + var resultStart = storage.Read(CreateRange(10, 10)); + var resultEnd = storage.Read(CreateRange(20, 20)); + + // ASSERT + Assert.Equal(1, resultStart.Length); + Assert.Equal(10, resultStart.Span[0]); + Assert.Equal(1, resultEnd.Length); + Assert.Equal(20, resultEnd.Span[0]); + } + + [Fact] + public void Read_AfterMultipleRematerializations_ReturnsCurrentData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 10, domain)); + storage.Rematerialize(CreateRangeData(50, 60, domain)); + storage.Rematerialize(CreateRangeData(100, 110, domain)); + + // ACT + var result = storage.Read(CreateRange(100, 110)); + + // ASSERT + VerifyDataMatchesRange(result, 100, 110); + } + + [Fact] + public void Read_OutOfBounds_ThrowsArgumentOutOfRangeException() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(10, 20, domain)); + + // ACT & ASSERT - Read beyond stored range + Assert.Throws(() => + storage.Read(CreateRange(25, 30))); + } + + [Fact] + public void Read_PartiallyOutOfBounds_ThrowsArgumentOutOfRangeException() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(10, 20, domain)); + + // ACT & ASSERT - Read overlapping but extending beyond range + Assert.Throws(() => + storage.Read(CreateRange(15, 25))); + } + + [Fact] + public void Read_BeforeStoredRange_ThrowsArgumentOutOfRangeException() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(10, 20, domain)); + + // ACT & ASSERT - Read before stored range + Assert.Throws(() => + storage.Read(CreateRange(0, 5))); + } + + #endregion + + #region ToRangeData Tests + + [Fact] + public void ToRangeData_AfterRematerialize_RoundTripsCorrectly() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + var originalData = CreateRangeData(10, 30, domain); + storage.Rematerialize(originalData); + + // ACT + var roundTripped = storage.ToRangeData(); + + // ASSERT + AssertRangeDataRoundTrip(originalData, roundTripped); + } + + [Fact] + public void ToRangeData_MaintainsSequentialOrder() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + var originalData = CreateRangeData(5, 15, domain); + storage.Rematerialize(originalData); + + // ACT + var rangeData = storage.ToRangeData(); + var dataArray = rangeData.Data.ToArray(); + + // ASSERT + for (var i = 0; i < dataArray.Length; i++) + { + Assert.Equal(5 + i, dataArray[i]); + } + } + + [Fact] + public void ToRangeData_AfterMultipleRematerializations_ReflectsCurrentState() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 10, domain)); + storage.Rematerialize(CreateRangeData(20, 30, domain)); + var finalData = CreateRangeData(100, 120, domain); + storage.Rematerialize(finalData); + + // ACT + var result = storage.ToRangeData(); + + // ASSERT + AssertRangeDataRoundTrip(finalData, result); + } + + #endregion + + #region Invariant B.11 Tests (Data/Range Consistency) + + [Fact] + public void InvariantB11_DataLengthMatchesRangeSize_AfterRematerialize() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + var rangeData = CreateRangeData(0, 50, domain); + + // ACT + storage.Rematerialize(rangeData); + var data = storage.Read(storage.Range); + + // ASSERT - Data length must equal range size (Invariant B.11) + var expectedLength = 51; // [0, 50] inclusive = 51 elements + Assert.Equal(expectedLength, data.Length); + } + + [Fact] + public void InvariantB11_DataLengthMatchesRangeSize_AfterMultipleRematerializations() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + // ACT & ASSERT - Verify consistency after each rematerialization + storage.Rematerialize(CreateRangeData(0, 10, domain)); + Assert.Equal(11, storage.Read(storage.Range).Length); + + storage.Rematerialize(CreateRangeData(0, 100, domain)); + Assert.Equal(101, storage.Read(storage.Range).Length); + + storage.Rematerialize(CreateRangeData(50, 55, domain)); + Assert.Equal(6, storage.Read(storage.Range).Length); + } + + [Fact] + public void InvariantB11_PartialReads_ConsistentWithStoredRange() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(10, 30, domain)); + + // ACT & ASSERT - All partial reads must be consistent with range + var read1 = storage.Read(CreateRange(10, 15)); + Assert.Equal(6, read1.Length); + VerifyDataMatchesRange(read1, 10, 15); + + var read2 = storage.Read(CreateRange(20, 25)); + Assert.Equal(6, read2.Length); + VerifyDataMatchesRange(read2, 20, 25); + + var read3 = storage.Read(CreateRange(25, 30)); + Assert.Equal(6, read3.Length); + VerifyDataMatchesRange(read3, 25, 30); + } + + #endregion + + #region Dual-Buffer Staging Pattern Tests + + [Fact] + public void StagingPattern_RematerializeWithDerivedData_WorksCorrectly() + { + // ARRANGE - Test scenario where rangeData.Data might be based on current storage + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 10, domain)); + + // ACT - Simulate expansion scenario: get current data and extend it + var currentData = storage.ToRangeData(); + var extendedData = currentData.Data.Concat(Enumerable.Range(11, 10)).ToArray(); + var extendedRange = CreateRange(0, 20); + var extendedRangeData = extendedData.ToRangeData(extendedRange, domain); + + storage.Rematerialize(extendedRangeData); + + // ASSERT - Data should be correct despite being derived from current storage + var result = storage.Read(CreateRange(0, 20)); + VerifyDataMatchesRange(result, 0, 20); + } + + [Fact] + public void StagingPattern_MultipleQuickRematerializations_MaintainsCorrectness() + { + // ARRANGE - Stress test the dual-buffer pattern + var domain = CreateFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + + // ACT - Rapid sequential rematerializations (buffer swapping) + for (var i = 0; i < 10; i++) + { + var start = i * 5; + var end = start + 5; + storage.Rematerialize(CreateRangeData(start, end, domain)); + } + + // ASSERT - Final state should be correct + var result = storage.Read(CreateRange(45, 50)); + VerifyDataMatchesRange(result, 45, 50); + } + + #endregion + + #region Domain-Agnostic Tests + + [Fact] + public void DomainAgnostic_WorksWithFixedStepDomain() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var storage = new CopyOnReadStorage(domain); + var rangeData = CreateRangeData(0, 100, domain); + + // ACT + storage.Rematerialize(rangeData); + var result = storage.Read(CreateRange(25, 75)); + + // ASSERT + VerifyDataMatchesRange(result, 25, 75); + } + + [Fact] + public void DomainAgnostic_WorksWithVariableStepDomain() + { + // ARRANGE + var steps = new[] { 1, 2, 5, 10, 20, 50, 100 }; + var domain = new IntegerVariableStepDomain(steps); + var storage = new CopyOnReadStorage(domain); + + var range = CreateRange(2, 50); + var data = new[] { 2, 5, 10, 20, 50 }; + var rangeData = data.ToRangeData(range, domain); + + // ACT + storage.Rematerialize(rangeData); + var result = storage.Read(CreateRange(2, 50)); + + // ASSERT + Assert.Equal(5, result.Length); + Assert.Equal(new[] { 2, 5, 10, 20, 50 }, result.ToArray()); + } + + #endregion +} diff --git a/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/SnapshotReadStorageTests.cs b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/SnapshotReadStorageTests.cs new file mode 100644 index 0000000..9a56808 --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/SnapshotReadStorageTests.cs @@ -0,0 +1,449 @@ +using Intervals.NET.Data.Extensions; +using Intervals.NET.Domain.Default.Numeric; +using SlidingWindowCache.Infrastructure.Storage; +using SlidingWindowCache.Public.Configuration; +using SlidingWindowCache.Unit.Tests.Infrastructure.Extensions; +using static SlidingWindowCache.Unit.Tests.Infrastructure.Storage.TestInfrastructure.StorageTestHelpers; + +namespace SlidingWindowCache.Unit.Tests.Infrastructure.Storage; + +/// +/// Unit tests for SnapshotReadStorage that verify the ICacheStorage interface contract, +/// data correctness (Invariant B.11), and error handling. +/// +public class SnapshotReadStorageTests +{ + #region Interface Contract Tests + + [Fact] + public void Mode_ReturnsSnapshot() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + // ACT + var mode = storage.Mode; + + // ASSERT + Assert.Equal(UserCacheReadMode.Snapshot, mode); + } + + [Fact] + public void Range_InitiallyEmpty() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + // ACT & ASSERT + // Default Range behavior - storage starts uninitialized + // Range is a value type, so it's always non-null + _ = storage.Range; + } + + [Fact] + public void Range_UpdatesAfterRematerialize() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + var rangeData = CreateRangeData(10, 20, domain); + + // ACT + storage.Rematerialize(rangeData); + + // ASSERT + Assert.Equal(10, storage.Range.Start.Value); + Assert.Equal(20, storage.Range.End.Value); + } + + #endregion + + #region Rematerialize Tests + + [Fact] + public void Rematerialize_StoresDataCorrectly() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + var rangeData = CreateRangeData(5, 15, domain); + + // ACT + storage.Rematerialize(rangeData); + var result = storage.Read(CreateRange(5, 15)); + + // ASSERT + VerifyDataMatchesRange(result, 5, 15); + } + + [Fact] + public void Rematerialize_UpdatesRange() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + var rangeData = CreateRangeData(100, 200, domain); + + // ACT + storage.Rematerialize(rangeData); + + // ASSERT + Assert.Equal(100, storage.Range.Start.Value); + Assert.Equal(200, storage.Range.End.Value); + } + + [Fact] + public void Rematerialize_MultipleCalls_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + // First rematerialization + var firstData = CreateRangeData(0, 10, domain); + storage.Rematerialize(firstData); + + // ACT - Second rematerialization with different range + var secondData = CreateRangeData(20, 30, domain); + storage.Rematerialize(secondData); + var result = storage.Read(CreateRange(20, 30)); + + // ASSERT + Assert.Equal(20, storage.Range.Start.Value); + Assert.Equal(30, storage.Range.End.Value); + VerifyDataMatchesRange(result, 20, 30); + } + + [Fact] + public void Rematerialize_WithSameSize_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 10, domain)); + + // ACT - Same size, different values + storage.Rematerialize(CreateRangeData(100, 110, domain)); + var result = storage.Read(CreateRange(100, 110)); + + // ASSERT + VerifyDataMatchesRange(result, 100, 110); + } + + [Fact] + public void Rematerialize_WithLargerSize_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 5, domain)); + + // ACT - Larger size + storage.Rematerialize(CreateRangeData(0, 20, domain)); + var result = storage.Read(CreateRange(0, 20)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 20); + } + + [Fact] + public void Rematerialize_WithSmallerSize_ReplacesData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT - Smaller size + storage.Rematerialize(CreateRangeData(0, 5, domain)); + var result = storage.Read(CreateRange(0, 5)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 5); + } + + #endregion + + #region Read Tests + + [Fact] + public void Read_FullRange_ReturnsAllData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 10, domain)); + + // ACT + var result = storage.Read(CreateRange(0, 10)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 10); + } + + [Fact] + public void Read_PartialRange_AtStart_ReturnsCorrectSubset() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT + var result = storage.Read(CreateRange(0, 5)); + + // ASSERT + VerifyDataMatchesRange(result, 0, 5); + } + + [Fact] + public void Read_PartialRange_InMiddle_ReturnsCorrectSubset() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT + var result = storage.Read(CreateRange(5, 15)); + + // ASSERT + VerifyDataMatchesRange(result, 5, 15); + } + + [Fact] + public void Read_PartialRange_AtEnd_ReturnsCorrectSubset() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 20, domain)); + + // ACT + var result = storage.Read(CreateRange(15, 20)); + + // ASSERT + VerifyDataMatchesRange(result, 15, 20); + } + + [Fact] + public void Read_SingleElement_ReturnsOneValue() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + storage.Rematerialize(CreateRangeData(0, 10, domain)); + + // ACT + var result = storage.Read(CreateRange(5, 5)); + + // ASSERT + Assert.Equal(1, result.Length); + Assert.Equal(5, result.Span[0]); + } + + [Fact] + public void Read_AtExactBoundaries_ReturnsCorrectData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + storage.Rematerialize(CreateRangeData(10, 20, domain)); + + // ACT + var resultStart = storage.Read(CreateRange(10, 10)); + var resultEnd = storage.Read(CreateRange(20, 20)); + + // ASSERT + Assert.Equal(1, resultStart.Length); + Assert.Equal(10, resultStart.Span[0]); + Assert.Equal(1, resultEnd.Length); + Assert.Equal(20, resultEnd.Span[0]); + } + + [Fact] + public void Read_AfterMultipleRematerializations_ReturnsCurrentData() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 10, domain)); + storage.Rematerialize(CreateRangeData(50, 60, domain)); + storage.Rematerialize(CreateRangeData(100, 110, domain)); + + // ACT + var result = storage.Read(CreateRange(100, 110)); + + // ASSERT + VerifyDataMatchesRange(result, 100, 110); + } + + #endregion + + #region ToRangeData Tests + + [Fact] + public void ToRangeData_AfterRematerialize_RoundTripsCorrectly() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + var originalData = CreateRangeData(10, 30, domain); + storage.Rematerialize(originalData); + + // ACT + var roundTripped = storage.ToRangeData(); + + // ASSERT + AssertRangeDataRoundTrip(originalData, roundTripped); + } + + [Fact] + public void ToRangeData_MaintainsSequentialOrder() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + var originalData = CreateRangeData(5, 15, domain); + storage.Rematerialize(originalData); + + // ACT + var rangeData = storage.ToRangeData(); + var dataArray = rangeData.Data.ToArray(); + + // ASSERT + for (var i = 0; i < dataArray.Length; i++) + { + Assert.Equal(5 + i, dataArray[i]); + } + } + + [Fact] + public void ToRangeData_AfterMultipleRematerializations_ReflectsCurrentState() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + storage.Rematerialize(CreateRangeData(0, 10, domain)); + storage.Rematerialize(CreateRangeData(20, 30, domain)); + var finalData = CreateRangeData(100, 120, domain); + storage.Rematerialize(finalData); + + // ACT + var result = storage.ToRangeData(); + + // ASSERT + AssertRangeDataRoundTrip(finalData, result); + } + + #endregion + + #region Invariant B.11 Tests (Data/Range Consistency) + + [Fact] + public void InvariantB11_DataLengthMatchesRangeSize_AfterRematerialize() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + var rangeData = CreateRangeData(0, 50, domain); + + // ACT + storage.Rematerialize(rangeData); + var data = storage.Read(storage.Range); + + // ASSERT - Data length must equal range size (Invariant B.11) + var expectedLength = 51; // [0, 50] inclusive = 51 elements + Assert.Equal(expectedLength, data.Length); + } + + [Fact] + public void InvariantB11_DataLengthMatchesRangeSize_AfterMultipleRematerializations() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + + // ACT & ASSERT - Verify consistency after each rematerialization + storage.Rematerialize(CreateRangeData(0, 10, domain)); + Assert.Equal(11, storage.Read(storage.Range).Length); + + storage.Rematerialize(CreateRangeData(0, 100, domain)); + Assert.Equal(101, storage.Read(storage.Range).Length); + + storage.Rematerialize(CreateRangeData(50, 55, domain)); + Assert.Equal(6, storage.Read(storage.Range).Length); + } + + [Fact] + public void InvariantB11_PartialReads_ConsistentWithStoredRange() + { + // ARRANGE + var domain = CreateFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + storage.Rematerialize(CreateRangeData(10, 30, domain)); + + // ACT & ASSERT - All partial reads must be consistent with range + var read1 = storage.Read(CreateRange(10, 15)); + Assert.Equal(6, read1.Length); + VerifyDataMatchesRange(read1, 10, 15); + + var read2 = storage.Read(CreateRange(20, 25)); + Assert.Equal(6, read2.Length); + VerifyDataMatchesRange(read2, 20, 25); + + var read3 = storage.Read(CreateRange(25, 30)); + Assert.Equal(6, read3.Length); + VerifyDataMatchesRange(read3, 25, 30); + } + + #endregion + + #region Domain-Agnostic Tests + + [Fact] + public void DomainAgnostic_WorksWithFixedStepDomain() + { + // ARRANGE + var domain = new IntegerFixedStepDomain(); + var storage = new SnapshotReadStorage(domain); + var rangeData = CreateRangeData(0, 100, domain); + + // ACT + storage.Rematerialize(rangeData); + var result = storage.Read(CreateRange(25, 75)); + + // ASSERT + VerifyDataMatchesRange(result, 25, 75); + } + + [Fact] + public void DomainAgnostic_WorksWithVariableStepDomain() + { + // ARRANGE + var steps = new[] { 1, 2, 5, 10, 20, 50, 100 }; + var domain = new IntegerVariableStepDomain(steps); + var storage = new SnapshotReadStorage(domain); + + var range = CreateRange(2, 50); + var data = new[] { 2, 5, 10, 20, 50 }; + var rangeData = data.ToRangeData(range, domain); + + // ACT + storage.Rematerialize(rangeData); + var result = storage.Read(CreateRange(2, 50)); + + // ASSERT + Assert.Equal(5, result.Length); + Assert.Equal(new[] { 2, 5, 10, 20, 50 }, result.ToArray()); + } + + #endregion +} diff --git a/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/TestInfrastructure/StorageTestHelpers.cs b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/TestInfrastructure/StorageTestHelpers.cs new file mode 100644 index 0000000..936581b --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/Infrastructure/Storage/TestInfrastructure/StorageTestHelpers.cs @@ -0,0 +1,81 @@ +using Intervals.NET; +using Intervals.NET.Data; +using Intervals.NET.Data.Extensions; +using Intervals.NET.Domain.Abstractions; +using Intervals.NET.Domain.Default.Numeric; + +namespace SlidingWindowCache.Unit.Tests.Infrastructure.Storage.TestInfrastructure; + +/// +/// Shared test helpers for storage implementation tests. +/// Provides factory methods for creating test data and assertion utilities. +/// +internal static class StorageTestHelpers +{ + /// + /// Creates a fixed-step integer domain for testing. + /// + public static IntegerFixedStepDomain CreateFixedStepDomain() => new(); + + /// + /// Creates a closed range for testing. + /// + public static Range CreateRange(int start, int end) => + Intervals.NET.Factories.Range.Closed(start, end); + + /// + /// Creates test range data with sequential integer values where value equals position. + /// For range [start, end], generates data [start, start+1, start+2, ..., end]. + /// + public static RangeData CreateRangeData( + int start, + int end, + IntegerFixedStepDomain domain) + { + var range = CreateRange(start, end); + var data = Enumerable.Range(start, end - start + 1).ToArray(); + return data.ToRangeData(range, domain); + } + + /// + /// Verifies that the provided data matches the expected range. + /// For range [start, end], expects data [start, start+1, ..., end]. + /// + public static void VerifyDataMatchesRange(ReadOnlyMemory actualData, int expectedStart, int expectedEnd) + { + var expectedLength = expectedEnd - expectedStart + 1; + Assert.Equal(expectedLength, actualData.Length); + + var span = actualData.Span; + for (var i = 0; i < span.Length; i++) + { + Assert.Equal(expectedStart + i, span[i]); + } + } + + /// + /// Verifies that ToRangeData() round-trips correctly by comparing ranges and data. + /// + public static void AssertRangeDataRoundTrip( + RangeData original, + RangeData roundTripped) + where TRange : IComparable + where TDomain : IRangeDomain + { + // Verify ranges match + Assert.Equal(original.Range.Start, roundTripped.Range.Start); + Assert.Equal(original.Range.End, roundTripped.Range.End); + Assert.Equal(original.Range.IsStartInclusive, roundTripped.Range.IsStartInclusive); + Assert.Equal(original.Range.IsEndInclusive, roundTripped.Range.IsEndInclusive); + + // Verify data matches + var originalArray = original.Data.ToArray(); + var roundTrippedArray = roundTripped.Data.ToArray(); + Assert.Equal(originalArray.Length, roundTrippedArray.Length); + + for (var i = 0; i < originalArray.Length; i++) + { + Assert.Equal(originalArray[i], roundTrippedArray[i]); + } + } +} \ No newline at end of file diff --git a/tests/SlidingWindowCache.Unit.Tests/Public/Configuration/WindowCacheOptionsTests.cs b/tests/SlidingWindowCache.Unit.Tests/Public/Configuration/WindowCacheOptionsTests.cs new file mode 100644 index 0000000..0b92f4f --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/Public/Configuration/WindowCacheOptionsTests.cs @@ -0,0 +1,650 @@ +using SlidingWindowCache.Public.Configuration; + +namespace SlidingWindowCache.Unit.Tests.Public.Configuration; + +/// +/// Unit tests for WindowCacheOptions that verify validation logic, property initialization, +/// and edge cases for cache configuration. +/// +public class WindowCacheOptionsTests +{ + #region Constructor - Valid Parameters Tests + + [Fact] + public void Constructor_WithValidParameters_InitializesAllProperties() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.5, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.4, + debounceDelay: TimeSpan.FromMilliseconds(200) + ); + + // ASSERT + Assert.Equal(1.5, options.LeftCacheSize); + Assert.Equal(2.0, options.RightCacheSize); + Assert.Equal(UserCacheReadMode.Snapshot, options.ReadMode); + Assert.Equal(0.3, options.LeftThreshold); + Assert.Equal(0.4, options.RightThreshold); + Assert.Equal(TimeSpan.FromMilliseconds(200), options.DebounceDelay); + } + + [Fact] + public void Constructor_WithMinimalParameters_UsesDefaults() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ); + + // ASSERT + Assert.Equal(1.0, options.LeftCacheSize); + Assert.Equal(1.0, options.RightCacheSize); + Assert.Equal(UserCacheReadMode.Snapshot, options.ReadMode); + Assert.Null(options.LeftThreshold); + Assert.Null(options.RightThreshold); + Assert.Equal(TimeSpan.FromMilliseconds(100), options.DebounceDelay); // Default + } + + [Fact] + public void Constructor_WithZeroCacheSizes_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 0.0, + rightCacheSize: 0.0, + readMode: UserCacheReadMode.Snapshot + ); + + // ASSERT + Assert.Equal(0.0, options.LeftCacheSize); + Assert.Equal(0.0, options.RightCacheSize); + } + + [Fact] + public void Constructor_WithZeroThresholds_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.0, + rightThreshold: 0.0 + ); + + // ASSERT + Assert.Equal(0.0, options.LeftThreshold); + Assert.Equal(0.0, options.RightThreshold); + } + + [Fact] + public void Constructor_WithNullThresholds_SetsThresholdsToNull() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: null, + rightThreshold: null + ); + + // ASSERT + Assert.Null(options.LeftThreshold); + Assert.Null(options.RightThreshold); + } + + [Fact] + public void Constructor_WithOnlyLeftThreshold_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, + rightThreshold: null + ); + + // ASSERT + Assert.Equal(0.2, options.LeftThreshold); + Assert.Null(options.RightThreshold); + } + + [Fact] + public void Constructor_WithOnlyRightThreshold_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: null, + rightThreshold: 0.2 + ); + + // ASSERT + Assert.Null(options.LeftThreshold); + Assert.Equal(0.2, options.RightThreshold); + } + + [Fact] + public void Constructor_WithLargeCacheSizes_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 100.0, + rightCacheSize: 200.0, + readMode: UserCacheReadMode.Snapshot + ); + + // ASSERT + Assert.Equal(100.0, options.LeftCacheSize); + Assert.Equal(200.0, options.RightCacheSize); + } + + [Fact] + public void Constructor_WithLargeThresholds_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.99, + rightThreshold: 1.0 + ); + + // ASSERT + Assert.Equal(0.99, options.LeftThreshold); + Assert.Equal(1.0, options.RightThreshold); + } + + [Fact] + public void Constructor_WithVerySmallDebounceDelay_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + debounceDelay: TimeSpan.FromMilliseconds(1) + ); + + // ASSERT + Assert.Equal(TimeSpan.FromMilliseconds(1), options.DebounceDelay); + } + + [Fact] + public void Constructor_WithVeryLargeDebounceDelay_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + debounceDelay: TimeSpan.FromSeconds(10) + ); + + // ASSERT + Assert.Equal(TimeSpan.FromSeconds(10), options.DebounceDelay); + } + + [Fact] + public void Constructor_WithSnapshotReadMode_SetsCorrectly() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ); + + // ASSERT + Assert.Equal(UserCacheReadMode.Snapshot, options.ReadMode); + } + + [Fact] + public void Constructor_WithCopyOnReadMode_SetsCorrectly() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.CopyOnRead + ); + + // ASSERT + Assert.Equal(UserCacheReadMode.CopyOnRead, options.ReadMode); + } + + #endregion + + #region Constructor - Validation Tests + + [Fact] + public void Constructor_WithNegativeLeftCacheSize_ThrowsArgumentOutOfRangeException() + { + // ARRANGE, ACT & ASSERT + var exception = Assert.Throws(() => + new WindowCacheOptions( + leftCacheSize: -1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ) + ); + + Assert.Equal("leftCacheSize", exception.ParamName); + Assert.Contains("LeftCacheSize must be greater than or equal to 0", exception.Message); + } + + [Fact] + public void Constructor_WithNegativeRightCacheSize_ThrowsArgumentOutOfRangeException() + { + // ARRANGE, ACT & ASSERT + var exception = Assert.Throws(() => + new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: -1.0, + readMode: UserCacheReadMode.Snapshot + ) + ); + + Assert.Equal("rightCacheSize", exception.ParamName); + Assert.Contains("RightCacheSize must be greater than or equal to 0", exception.Message); + } + + [Fact] + public void Constructor_WithNegativeLeftThreshold_ThrowsArgumentOutOfRangeException() + { + // ARRANGE, ACT & ASSERT + var exception = Assert.Throws(() => + new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: -0.1 + ) + ); + + Assert.Equal("leftThreshold", exception.ParamName); + Assert.Contains("LeftThreshold must be greater than or equal to 0", exception.Message); + } + + [Fact] + public void Constructor_WithNegativeRightThreshold_ThrowsArgumentOutOfRangeException() + { + // ARRANGE, ACT & ASSERT + var exception = Assert.Throws(() => + new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + rightThreshold: -0.1 + ) + ); + + Assert.Equal("rightThreshold", exception.ParamName); + Assert.Contains("RightThreshold must be greater than or equal to 0", exception.Message); + } + + [Fact] + public void Constructor_WithVerySmallNegativeLeftCacheSize_ThrowsArgumentOutOfRangeException() + { + // ARRANGE, ACT & ASSERT + var exception = Assert.Throws(() => + new WindowCacheOptions( + leftCacheSize: -0.001, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ) + ); + + Assert.Equal("leftCacheSize", exception.ParamName); + } + + [Fact] + public void Constructor_WithVerySmallNegativeRightCacheSize_ThrowsArgumentOutOfRangeException() + { + // ARRANGE, ACT & ASSERT + var exception = Assert.Throws(() => + new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: -0.001, + readMode: UserCacheReadMode.Snapshot + ) + ); + + Assert.Equal("rightCacheSize", exception.ParamName); + } + + #endregion + + #region Record Equality Tests + + [Fact] + public void RecordEquality_WithSameValues_AreEqual() + { + // ARRANGE + var options1 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.4, + debounceDelay: TimeSpan.FromMilliseconds(100) + ); + + var options2 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.4, + debounceDelay: TimeSpan.FromMilliseconds(100) + ); + + // ACT & ASSERT + Assert.Equal(options1, options2); + Assert.True(options1 == options2); + Assert.False(options1 != options2); + } + + [Fact] + public void RecordEquality_WithDifferentLeftCacheSize_AreNotEqual() + { + // ARRANGE + var options1 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ); + + var options2 = new WindowCacheOptions( + leftCacheSize: 2.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ); + + // ACT & ASSERT + Assert.NotEqual(options1, options2); + Assert.False(options1 == options2); + Assert.True(options1 != options2); + } + + [Fact] + public void RecordEquality_WithDifferentRightCacheSize_AreNotEqual() + { + // ARRANGE + var options1 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ); + + var options2 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot + ); + + // ACT & ASSERT + Assert.NotEqual(options1, options2); + } + + [Fact] + public void RecordEquality_WithDifferentReadMode_AreNotEqual() + { + // ARRANGE + var options1 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot + ); + + var options2 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.CopyOnRead + ); + + // ACT & ASSERT + Assert.NotEqual(options1, options2); + } + + [Fact] + public void RecordEquality_WithDifferentThresholds_AreNotEqual() + { + // ARRANGE + var options1 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2 + ); + + var options2 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3 + ); + + // ACT & ASSERT + Assert.NotEqual(options1, options2); + } + + [Fact] + public void RecordEquality_WithDifferentDebounceDelay_AreNotEqual() + { + // ARRANGE + var options1 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + debounceDelay: TimeSpan.FromMilliseconds(100) + ); + + var options2 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + debounceDelay: TimeSpan.FromMilliseconds(200) + ); + + // ACT & ASSERT + Assert.NotEqual(options1, options2); + } + + [Fact] + public void GetHashCode_WithSameValues_ReturnsSameHashCode() + { + // ARRANGE + var options1 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.4 + ); + + var options2 = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 2.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.3, + rightThreshold: 0.4 + ); + + // ACT & ASSERT + Assert.Equal(options1.GetHashCode(), options2.GetHashCode()); + } + + #endregion + + #region Edge Cases and Boundary Tests + + [Fact] + public void Constructor_WithBothCacheSizesZero_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 0.0, + rightCacheSize: 0.0, + readMode: UserCacheReadMode.Snapshot + ); + + // ASSERT + Assert.Equal(0.0, options.LeftCacheSize); + Assert.Equal(0.0, options.RightCacheSize); + } + + [Fact] + public void Constructor_WithBothThresholdsNull_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: null, + rightThreshold: null + ); + + // ASSERT + Assert.Null(options.LeftThreshold); + Assert.Null(options.RightThreshold); + } + + [Fact] + public void Constructor_WithZeroDebounceDelay_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + debounceDelay: TimeSpan.Zero + ); + + // ASSERT + Assert.Equal(TimeSpan.Zero, options.DebounceDelay); + } + + [Fact] + public void Constructor_WithNullDebounceDelay_UsesDefault() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 1.0, + rightCacheSize: 1.0, + readMode: UserCacheReadMode.Snapshot, + debounceDelay: null + ); + + // ASSERT + Assert.Equal(TimeSpan.FromMilliseconds(100), options.DebounceDelay); + } + + [Fact] + public void Constructor_WithVeryLargeCacheSizes_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: double.MaxValue, + rightCacheSize: double.MaxValue, + readMode: UserCacheReadMode.Snapshot + ); + + // ASSERT + Assert.Equal(double.MaxValue, options.LeftCacheSize); + Assert.Equal(double.MaxValue, options.RightCacheSize); + } + + [Fact] + public void Constructor_WithVerySmallPositiveValues_IsValid() + { + // ARRANGE & ACT + var options = new WindowCacheOptions( + leftCacheSize: 0.0001, + rightCacheSize: 0.0001, + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.0001, + rightThreshold: 0.0001 + ); + + // ASSERT + Assert.Equal(0.0001, options.LeftCacheSize); + Assert.Equal(0.0001, options.RightCacheSize); + Assert.Equal(0.0001, options.LeftThreshold); + Assert.Equal(0.0001, options.RightThreshold); + } + + #endregion + + #region Documentation and Usage Scenario Tests + + [Fact] + public void Constructor_TypicalCacheScenario_WorksAsExpected() + { + // ARRANGE & ACT - Typical sliding window cache with symmetric caching + var options = new WindowCacheOptions( + leftCacheSize: 1.0, // Cache same size as requested range on left + rightCacheSize: 1.0, // Cache same size as requested range on right + readMode: UserCacheReadMode.Snapshot, + leftThreshold: 0.2, // Rebalance when 20% of cache remains + rightThreshold: 0.2, + debounceDelay: TimeSpan.FromMilliseconds(50) + ); + + // ASSERT + Assert.Equal(1.0, options.LeftCacheSize); + Assert.Equal(1.0, options.RightCacheSize); + Assert.Equal(0.2, options.LeftThreshold); + Assert.Equal(0.2, options.RightThreshold); + } + + [Fact] + public void Constructor_ForwardOnlyScenario_WorksAsExpected() + { + // ARRANGE & ACT - Optimized for forward-only access (e.g., video streaming) + var options = new WindowCacheOptions( + leftCacheSize: 0.0, // No left cache needed + rightCacheSize: 2.0, // Large right cache for forward access + readMode: UserCacheReadMode.Snapshot, + leftThreshold: null, + rightThreshold: 0.3 + ); + + // ASSERT + Assert.Equal(0.0, options.LeftCacheSize); + Assert.Equal(2.0, options.RightCacheSize); + Assert.Null(options.LeftThreshold); + Assert.Equal(0.3, options.RightThreshold); + } + + [Fact] + public void Constructor_MinimalRebalanceScenario_WorksAsExpected() + { + // ARRANGE & ACT - Disable automatic rebalancing + var options = new WindowCacheOptions( + leftCacheSize: 0.5, + rightCacheSize: 0.5, + readMode: UserCacheReadMode.CopyOnRead, + leftThreshold: null, // Disable left threshold + rightThreshold: null // Disable right threshold + ); + + // ASSERT + Assert.Null(options.LeftThreshold); + Assert.Null(options.RightThreshold); + } + + #endregion +} diff --git a/tests/SlidingWindowCache.Unit.Tests/SlidingWindowCache.Unit.Tests.csproj b/tests/SlidingWindowCache.Unit.Tests/SlidingWindowCache.Unit.Tests.csproj new file mode 100644 index 0000000..3e123f5 --- /dev/null +++ b/tests/SlidingWindowCache.Unit.Tests/SlidingWindowCache.Unit.Tests.csproj @@ -0,0 +1,31 @@ + + + + net8.0 + enable + enable + + false + true + + + + + + + + + + + + + + + + + + + + + +