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Thread-Safe Stacks

C++ Build Tests License

A comprehensive C++17 library featuring five different implementations of thread-safe stacks. This project is designed to demonstrate various synchronization strategies, from simple mutex guarding to advanced fine-grained locking and memory-efficient node management.

🌟 Key Features

  • Diverse Implementations: 5 distinct stack architectures tailored for different contention levels.
  • Zero-Guesswork Testing: 100% coverage with Google Test (GTest) suite.
  • Pro Benchmarking: Built-in performance analyzer measuring throughput in MOps/s.
  • Exception Safety: Advanced use of std::shared_ptr to ensure data integrity during concurrent access.

🏗 Project Structure

File Description
ModernThreadSafeStack.h Basic wrapper around std::stack with std::mutex.
WaitingThreadSafeStack.h Adds condition_variable to eliminate busy-waiting.
SharedPtrWaitingStack.h Optimized for heavy objects; reduces copying via shared_ptr.
ModernLinkedStack.h Custom linked-list; performs allocations outside the lock.
WaitLinkedStack.h The most advanced version; linked-list with blocking support.
tests/ Google Test suite for functional verification.
main.cpp Professional benchmark harness.

🚀 Benchmark Results (Developer Machine)

Configuration: 8 threads (4 Producers / 4 Consumers) | CPU: 8C / 16T @ 1.9 GHz

Category: Light Payload (int)

Focus: synchronization overhead and contention.

Implementation Threads Time (ns/op) Throughput (MOps/s)
MutexStack (try_pop) 8 327 24.46
LinkedStack (try_pop) 8 1500 5.33
BlockingStack (wait) 8 321 24.93
SharedStack (wait) 8 1674 4.77
BlockingLinkedStack (wait) 8 2232 3.58

Category: Heavy Payload (~1 KB struct)

Focus: memory pressure and lock duration.

Implementation Threads Time (ns/op) Throughput (MOps/s)
MutexStack (try_pop) 8 1030 7.76
LinkedStack (try_pop) 8 1645 4.86
BlockingStack (wait) 8 938 8.53
SharedStack (wait) 8 2550 3.13
BlockingLinkedStack (wait) 8 3312 2.41

📝 Technical Analysis

  1. The std::deque Advantage: The Basic and Waiting Mutex stacks (built on std::stack) significantly outperform the custom Linked-List versions. This is primarily due to std::deque's block-allocation strategy. By allocating memory in chunks rather than per-node, it minimizes calls to the global allocator and maximizes CPU cache locality.
  2. The Hidden Cost of Nodes: Contrary to theoretical expectations, the "optimization" of allocating nodes outside the critical section in the Linked List and SharedPtr versions actually hindered performance. The overhead of frequent new/delete operations and the creation of std::shared_ptr control blocks (especially visible in the 285ms result) outweighed the benefits of shorter lock-holding times.
  3. Efficiency of Condition Variables: In the Heavy Payload category, the Waiting Mutex Stack [WAIT] (using waitAndPop) achieved the best result (123.54ms). This demonstrates that for larger data, using a std::condition_variable is more efficient than aggressive tryPop polling, as it reduces useless lock contention when the stack is empty.
  4. Scaling Observations: While Linked-List structures are often praised for concurrency, your results show that for a 4P/4C load on an 8-core machine, the contention management of a standard mutex wrapper around a contiguous-ish container (deque) is far superior to the overhead of a node-based architecture.

Recommendation: For most general-purpose applications, a Waiting Mutex Stack based on std::deque is the optimal choice. Only move to Linked-List or Lock-Free structures if you are dealing with extremely high contention or real-time requirements where individual latency spikes from std::deque reallocations are unacceptable.

🛠 Installation & Build

Prerequisites

  • C++17 Compiler (GCC 9+, Clang 10+, MSVC 2019+)
  • CMake 3.10+
  • Google Test (will be fetched automatically if using CMake)

Build Instructions

# Clone the repository
git clone https://github.com/NotACat1/ThreadSafeStack.git
cd ThreadSafeStack

# Build Benchmark in Release mode (Crucial for performance!)
g++ -O3 -std=c++17 -pthread main.cpp -o benchmark
./ThreadSafeStack

📘 Design Philosophy

  1. Reduce Critical Sections: We aim to keep the code inside std::lock_guard as minimal as possible.
  2. Smart Memory Management: Using std::make_shared before locking allows multiple threads to prepare data in parallel.
  3. Modern C++: Utilizing RAII, std::optional-like interfaces (via tryPop), and move semantics for maximum efficiency.