Debugging a Race Condition in Legacy C++ Application During Migration to C++17
I'm dealing with I'm building a feature where During our migration project from an older version of C++ to C++17, I stumbled upon a troublesome race condition in our legacy application. The application, originally built with C++11, utilizes several threads to process data concurrently, which has been running fine for years. However, after updating the compiler and libraries, I've noticed sporadic crashes. While analyzing the code, I found a section where threads access shared resources without proper synchronization. The code looks something like this: ```cpp #include <iostream> #include <thread> #include <vector> #include <atomic> std::vector<int> data; std::atomic<int> counter{0}; void processData(int id) { for (int i = 0; i < 1000; ++i) { data.push_back(id * 1000 + i); ++counter; } } int main() { std::thread t1(processData, 1); std::thread t2(processData, 2); t1.join(); t2.join(); std::cout << "Counter: " << counter.load() << "\n"; return 0; } ``` The application crashes intermittently, and I've attempted to resolve it by introducing a mutex, but it seems to have introduced significant performance bottlenecks. Here’s my modified version: ```cpp #include <mutex> std::mutex mtx; void processData(int id) { for (int i = 0; i < 1000; ++i) { std::lock_guard<std::mutex> lock(mtx); data.push_back(id * 1000 + i); ++counter; } } ``` While this resolved the crashes, I'm concerned about the performance implications. The original application was designed for high throughput, and adding mutex locks seems to degrade that. I also thought about using `std::shared_mutex` for read-heavy sections, but the writes would still block reads entirely. Another approach I considered was to use `std::atomic` for managing `data`, but I’m not sure how to store complex types atomically. Any suggestions on better synchronization mechanisms or patterns for optimizing the performance while ensuring thread safety? Additionally, would it be beneficial to restructure the code to use concurrent data structures, such as those provided by Intel's Threading Building Blocks or similar libraries? Insights from anyone who has tackled similar legacy migration projects or race conditions would be greatly appreciated. I'm using C++ 3.11 in this project. Hoping someone can shed some light on this. I appreciate any insights!