C++ 20 Coroutines with `std::future` Resulting in Unexpected Behavior on GCC 11.2
I'm currently working on a project that utilizes C++ 20 coroutines along with `std::future` to handle asynchronous tasks. However, I'm running into an issue where the future seems to be getting resolved before the coroutine actually completes its execution, leading to unpredictable behavior. The code snippet below demonstrates the issue: ```cpp #include <iostream> #include <future> #include <coroutine> #include <chrono> struct Task { struct promise_type { Task get_return_object() { return {}; } std::suspend_never initial_suspend() { return {}; } std::suspend_always final_suspend() noexcept { return {}; } void unhandled_exception() { std::terminate(); } void return_void() {} }; }; Task async_task() { std::cout << "Task started\n"; std::this_thread::sleep_for(std::chrono::seconds(2)); std::cout << "Task completed\n"; } int main() { auto future = std::async(std::launch::async, async_task); auto result = future.get(); // This is where I suspect the issue is. std::cout << "Future completed\n"; return 0; } ``` When I run this program, the output is: 1. "Task started" 2. "Future completed" 3. "Task completed" It seems like the `future.get()` is resolving before `async_task()` actually completes, which results in misleading output. I've checked that I'm calling `std::async` correctly, and I've also tried using `std::promise` instead of `std::future`, but the result is similar. I've verified that I'm using GCC 11.2 and have the flag `-std=c++20` set. Is there a specific reason why `std::async` is behaving this way with coroutines? Is there a better approach to ensure that the future correctly waits for the coroutine to complete? Any help would be greatly appreciated! I'm on Windows 10 using the latest version of C++.