Race condition in concurrent file writing with std::mutex in C++11
I've searched everywhere and can't find a clear answer. I'm experiencing a race condition while trying to write to a log file from multiple threads in C++11. I'm using `std::mutex` to synchronize access to the file, but sometimes the logs seem to interleave or are truncated. Below is a simplified version of my code: ```cpp #include <iostream> #include <fstream> #include <thread> #include <mutex> #include <vector> std::mutex fileMutex; std::ofstream logFile; void writeLog(int threadId, const std::string& message) { std::lock_guard<std::mutex> lock(fileMutex); logFile << "Thread " << threadId << ": " << message << std::endl; } void threadFunction(int id) { for (int i = 0; i < 5; ++i) { writeLog(id, "Log entry " + std::to_string(i)); } } int main() { logFile.open("log.txt", std::ios::app); std::vector<std::thread> threads; for (int i = 0; i < 3; ++i) { threads.emplace_back(threadFunction, i); } for (auto& th : threads) { th.join(); } logFile.close(); return 0; } ``` I'm initializing the file in `main()` and ensuring that I lock the mutex around the `logFile` writes. Despite this, I'm still seeing that some log entries get overwritten or appear incomplete. I suspect it might be due to how the output buffer is handled or perhaps an scenario with the file stream's state. I've also tried flushing the stream manually with `logFile.flush()`, but it didn't solve the question. Is there something I'm missing in my synchronization approach, or any specific considerations I should be aware of regarding file I/O in a multithreaded context? My development environment is macOS.