Summary

This PR strengthens thread_system's foundation by enforcing common_system dependency and adding comprehensive runtime metrics:

1. Required Dependency on common_system

   • Enforce common_system availability at CMake configuration time
   • Ensure IExecutor interface compatibility
   • Align with unified build system architecture

2. Runtime Performance Metrics

   • Thread pool metrics collection and tracking
   • Job lifecycle monitoring (submission, completion, rejection)
   • Queue depth and worker utilization metrics

Changes

Build System

• Add fatal error when common_system is not available
• Update ThreadSystemDependencies.cmake for proper detection
• Ensure unified build integration

Metrics Infrastructure

• New ThreadPoolMetrics class with atomic counters
• Track job counts, queue depth, worker activity
• Provide read-only access and reset functionality

Thread Pool Integration

• Add metrics() accessor to ThreadPool
• Integrate metrics collection in job submission path
• Update workers to record completion events
• Maintain zero-overhead when metrics not accessed

API Changes

New Public Methods

const metrics::ThreadPoolMetrics& thread_pool::metrics() const noexcept;
void thread_pool::reset_metrics();

Breaking Changes

• thread_system now REQUIRES common_system
• Projects must link against common_system

Testing

• Builds with common_system dependency
• Metrics accumulate correctly
• Reset functionality works
• No performance regression

Migration Guide

For standalone builds:

set(BUILD_WITH_COMMON_SYSTEM ON)
find_package(common_system REQUIRED)
target_link_libraries(your_target PRIVATE thread_system)

Performance Impact

• Metrics use atomic operations (minimal overhead)
• No impact when metrics not accessed
• Reset operation is O(1)

Linked PR: #92 Enforce common_system dependency and add runtime metrics