SystemInfoApp

An Objective-C app being developed in Xcode to help me learn how to interact with macOS system-level APIs. It will display real-time information about the system including CPU, disk, memory, and network usage.

Software Details

Main Dashboard

A vertical Split View is used to divide the left half of the main dashboard from the right. The left side contains a cell-based Table View that is connected to the Main Dashboard Controller. The Main Dashboard Controller adheres to the NSTableViewDelegate and NSTableViewDataSource protocols. numberOfRowsInTableView provides the number of rows in the table and tableView:objectValueForTableColumn:row: provides the string used in each table cell.

CPU Monitor

The CPUModel provides a static function called overallCPUPercent as an interface to calculate the CPU usage across the system.

Calculating CPU Usage

overallCPUPercent uses the Mach library's host_processor_info function to get CPU tick information for each processor core. For each core the used ticks are added to a global total using CPU_STATE_USER and CPU_STATE_SYSTEM and the idle ticks are collected from CPU_STATE_IDLE. Once the values of these are summed from all cores, the overall CPU usage on the system can be calculated by:

Total CPU Usage Percent = ( used ticks / ( used ticks + idle ticks )) * 100

Displaying the CPU usage in the view

The CPUViewController uses NSTimer to call overallCPUPercent every few seconds based on the value returned by the PreferencesModel's getRefreshRatePreference method.

Memory Monitor

The MemoryModel provides a static function called getMemoryUsage as an interface to calculate the memory usage across the system. It returns a MemoryInfo struct with the following data:

struct MemoryInfo {
    double totalPhysicalMemoryGB;       // Total physical memory available in GB
    double totalMemoryUsedGB;           // Active + Wire memory used in GB
    double activeMemoryUsedGB;          // Active memory used in GB
    double wireMemoryUsedGB;            // Wired memory used in GB
    double totalMemoryUsedPercent;      // Percent of (active + wired) memory used over total physical
};

Calculating Memory Usage

getMemoryUsage uses the Mach library's host_statistics64 function to get the number of free_count, inactive_count, active_count, and wire_count from virtual memory using the vm_statistics64_data_t struct.

Page counts are converted to GB using a conversion factor of: (vm_page_size * (1 / 1073741824)). 1073741824 is 2^30 which is the number of bytes in a GB.

• totalPhysicalMemoryGB is calculated by adding the free, inactive, active, and wire page counts, converted to GB.
• totalMemoryUsedGB is calculated by adding the active and wire page counts, converted to GB.
• totalMemoryUsedPercent is calculated by (totalMemoryUsedGB / totalPhysicalMemoryGB) * 100;
• activeMemoryUsedGB and wireMemoryUsedGB are reported directly from the outputs of host_statistics64 after being converted to GB.

Displaying the memory usage in the view

The MemoryViewController uses NSTimer to call updateMemoryUsage every few seconds based on the value returned by the PreferencesModel's getRefreshRatePreference method.

Preferences

The PreferencesModel interacts with the NSUserDefaults system API to save and update the following user preferences

• Window Appearance: Users can choose to have the application window in Dark Mode, Light Mode, or match whatever their System Default is.
• Live Monitoring Refresh Rate Users can change the refresh rate of the live monitoring pages with this setting,

Development Environment

Due to the constraints of developing on a late 2012 iMac, some of my code may incorporate older practices or APIs. For clarity and transparency, I've outlined my development environment details below.

Clang Compiler Version

Apple clang version 12.0.0 (clang-1200.0.32.29)
Target: x86_64-apple-darwin19.6.0
Thread model: posix

Xcode version

Version 12.4 (12D4e)

Operating System

OSX Catalina 10.15.7