C++20 coroutines and lambda capturing leading to advanced patterns in asynchronous tasks
I'm integrating two systems and I'm converting an old project and I've searched everywhere and can't find a clear answer... I'm working on a personal project and I'm working on a project and hit a roadblock... I'm currently working on a project that leverages C++20 coroutines for asynchronous tasks, and I've run into a peculiar scenario when using lambdas that capture local variables. The behavior is inconsistent, and I'm struggling to understand why. Here’s a simplified version of my code: ```cpp #include <iostream> #include <coroutine> #include <future> #include <thread> struct Task { struct promise_type { Task get_return_object() { return {}; } std::suspend_never initial_suspend() { return {}; } std::suspend_never final_suspend() noexcept { return {}; } void return_void() {} void unhandled_exception() { std::terminate(); } }; }; void asyncTask(int id) { auto lambda = [id]() -> Task { std::cout << "Task " << id << " is running on thread: " << std::this_thread::get_id() << '\n'; co_return; }; lambda(); } int main() { std::thread t1(asyncTask, 1); std::thread t2(asyncTask, 2); t1.join(); t2.join(); return 0; } ``` When I run this, I expect to see each task's output indicating it's being run on different threads, but sometimes the outputs get mixed up, and I see unexpected behavior. I also notice that if I change the lambda to capture by reference instead of by value, it leads to a crash due to accessing invalid memory. I've tried using `std::shared_ptr` to manage the capture, but that doesn't seem to resolve the question either. Additionally, I enabled the coroutine debug mode, and I’m getting warnings about accessing destroyed objects, which makes me wonder if the lifetime of the captured variables is being managed correctly. Is there a specific way I should be capturing variables in coroutines to avoid these issues? What are the best practices for using coroutines with lambdas in this context? Any insights would be greatly appreciated. For context: I'm using C++ on Ubuntu. Has anyone else encountered this? My development environment is Linux. Any help would be greatly appreciated! Any examples would be super helpful. Is there a simpler solution I'm overlooking?