👀 Views: 50 💬 Answers: 1 📅 Created: 2025-07-03

cpp multithreading shared_ptr C++

I'm confused about I'm writing unit tests and I'm working with an scenario with inconsistent output when using `std::thread` in conjunction with `std::shared_ptr` in a C++11 application... I'm trying to parallelize a function that processes elements in a vector, but sometimes the results are not what I expect. Here’s a simplified version of my code: ```cpp #include <iostream> #include <vector> #include <thread> #include <memory> #include <mutex> std::mutex io_mutex; void processElement(std::shared_ptr<int> element) { // Simulate some processing *element *= 2; std::lock_guard<std::mutex> lock(io_mutex); std::cout << "Processed: " << *element << '\n'; } int main() { std::vector<std::shared_ptr<int>> numbers; for (int i = 0; i < 10; ++i) { numbers.push_back(std::make_shared<int>(i)); } std::vector<std::thread> threads; for (auto& num : numbers) { threads.emplace_back(processElement, num); } for (auto& thread : threads) { thread.join(); } return 0; } ``` The output I sometimes get is not consistent; for example, occasionally I'll see numbers being processed that don’t seem to match the original values. I’ve thought about the possibility of race conditions, but given that I’m using `std::shared_ptr` and locking the output with `std::mutex`, I didn’t expect this scenario. Additionally, I’ve tried removing the `std::mutex` and saw similar inconsistent behavior, which makes me think the question might be elsewhere in my code. I’m using g++ 9.3.0 on Linux. Any insights on what might be causing this inconsistent processing and how to resolve it would be greatly appreciated! This is part of a larger REST API I'm building. Thanks, I really appreciate it! I'm working with C++ in a Docker container on Debian. I'm open to any suggestions.