👀 Views: 0 💬 Answers: 1 📅 Created: 2025-07-27

c++ multithreading optional mutex c++17 cpp

I'm integrating two systems and I'm working on a personal project and I've searched everywhere and can't find a clear answer..... I'm facing an issue where `std::optional` seems to not be populated correctly when accessed from multiple threads in my C++17 application. I have a function that initializes an `std::optional` object in one thread, but when I try to access it from another thread, it appears to be empty even though it should have been populated. Here’s a simplified version of what I’m doing: ```cpp #include <iostream> #include <thread> #include <optional> #include <mutex> std::optional<int> sharedValue; std::mutex mtx; void setValue() { std::lock_guard<std::mutex> lock(mtx); sharedValue = 42; } void getValue() { std::lock_guard<std::mutex> lock(mtx); if (sharedValue) { std::cout << "Value: " << *sharedValue << "\n"; } else { std::cout << "Value not set!\n"; } } int main() { std::thread t1(setValue); std::thread t2(getValue); t1.join(); t2.join(); return 0; } ``` In this code, I'm using a `std::mutex` to synchronize access to `sharedValue`. However, when I run it, sometimes I see the output `Value not set!`, which suggests that `getValue` is checking `sharedValue` before `setValue` has finished initializing it. I was expecting that the `std::lock_guard` would prevent this race condition, but it seems like the timing is off. I’ve tried running the threads in different orders, and I even added sleep calls to simulate delays, but the issue persists. Is there something I'm missing in how I'm using `std::optional` or `std::mutex`? Any suggestions on how to ensure that the value is correctly set and read? I appreciate any insights! I'm working on a CLI tool that needs to handle this. Thanks in advance!