reusing nodes by extracting

libraries/multi-index-lru/include/userver/multi-index-lru/container.hpp

@@ -4,6 +4,7 @@
 /// @brief @copybrief multi_index_lru::Container
 
 #include "impl/mpl_helpers.hpp"
+#include <vector>
 
 USERVER_NAMESPACE_BEGIN
 
@@ -25,12 +26,23 @@ class Container {
     template <typename... Args>
     auto emplace(Args&&... args) {
         auto& seq_index = get_sequenced();
-        auto result = seq_index.emplace_front(std::forward<Args>(args)...);
 
+        std::pair<decltype(seq_index.begin()), bool> result;
+
+        if (free_nodes_.size() > 0) {
+            auto node = std::move(free_nodes_.back());
+            free_nodes_.pop_back();
+
+            node.value() =  Value(std::forward<Args>(args)...);
+            auto ret = seq_index.insert(seq_index.begin(), std::move(node));
+            result = {ret.position, ret.inserted};
+        } else {
+            result = seq_index.emplace_front(std::forward<Args>(args)...);
+        }
         if (!result.second) {
             seq_index.relocate(seq_index.begin(), result.first);
         } else if (seq_index.size() > max_size_) {
-            seq_index.pop_back();
+            free_nodes_.emplace_back(seq_index.extract(std::prev(seq_index.end())));
         }
         return result;
     }
@@ -91,7 +103,10 @@ class Container {
 
     template <typename Tag, typename Key>
     bool erase(const Key& key) {
-        return get_index<Tag>().erase(key) > 0;
+        auto it = find_no_update<Tag, Key>(key);
+        if (it == end<Tag>()) return false;
+        free_nodes_.emplace_back(container_.template get<Tag>().extract(it));
+        return true;
     }
 
     std::size_t size() const noexcept { return container_.size(); }
@@ -102,7 +117,7 @@ class Container {
         max_size_ = new_capacity;
         auto& seq_index = get_sequenced();
         while (container_.size() > max_size_) {
-            seq_index.pop_back();
+            free_nodes_.emplace_back(seq_index.extract(std::prev(seq_index.end())));
         }
     }
 
@@ -122,6 +137,7 @@ class Container {
 
     BoostContainer container_;
     std::size_t max_size_;
+    std::vector<typename BoostContainer::node_type> free_nodes_;
 
     auto& get_sequenced() noexcept { return container_.template get<0>(); }
 

libraries/multi-index-lru/include/userver/multi-index-lru/expirable_container.hpp

@@ -22,7 +22,8 @@ class ExpirableContainer {
         : container_(max_size),
           ttl_(ttl)
     {
-        UASSERT_MSG(ttl.count() > 0, "ttl must be positive");
+        UINVARIANT(ttl.count() > 0, "ttl must be positive");
+        UINVARIANT(max_size > 0, "capacity must be positive");
     }
 
     template <typename... Args>

libraries/multi-index-lru/src/expirable_container_test.cpp

@@ -305,6 +305,42 @@ UTEST_F(ExpirableUsersTest, ThreadSafetyBasic) {
     EXPECT_LE(cache.size(), 100);
 }
 
+#ifdef NDEBUG
+
+UTEST_F(ExpirableUsersTest, ZeroTTL) {
+    using namespace std::chrono_literals;
+
+    EXPECT_THROW(
+        {
+            UserCacheExpirable cache(10, 0ms);
+        },
+        utils::InvariantError
+    );
+}
+
+UTEST_F(ExpirableUsersTest, ZeroCapacity) {
+    using namespace std::chrono_literals;
+
+    EXPECT_THROW(
+        {
+            UserCacheExpirable cache(0, 10s);
+        },
+        utils::InvariantError
+    );
+}
+
+UTEST_F(ExpirableUsersTest, NegativeTTL) {
+    using namespace std::chrono_literals;
+
+    EXPECT_THROW(
+        {
+            UserCacheExpirable cache(10, -1ms);
+        },
+        utils::InvariantError
+    );
+}
+#endif
+
 }  // namespace
 
 USERVER_NAMESPACE_END