👀 Views: 443 💬 Answers: 1 📅 Created: 2025-06-10

C++17 thread-pool future std::promise C++

I tried several approaches but none seem to work. I've hit a wall trying to I'm working on a project and hit a roadblock... I'm working with an scenario where my `std::future` seems to be exploring on the shared state when I'm trying to retrieve the result of an asynchronous computation using a custom thread pool. I'm using C++17 and have implemented a simple thread pool that creates a fixed number of worker threads. The question arises when I submit a task to the thread pool and immediately attempt to get the result using `get()`. Here’s a simplified version of my code: ```cpp #include <future> #include <iostream> #include <vector> #include <thread> #include <queue> #include <condition_variable> #include <functional> class ThreadPool { public: ThreadPool(size_t threads); template<class F> auto enqueue(F&& f) -> std::future<decltype(f())>; ~ThreadPool(); private: std::vector<std::thread> workers; std::queue<std::function<void()>> tasks; std::mutex queue_mutex; std::condition_variable condition; bool stop; }; ThreadPool::ThreadPool(size_t threads) : stop(false) { for (size_t i = 0; i < threads; ++i) { workers.emplace_back([this] { for (;;) { std::function<void()> task; { std::unique_lock<std::mutex> lock(this->queue_mutex); this->condition.wait(lock, [this]{ return this->stop || !this->tasks.empty(); }); if (this->stop && this->tasks.empty()) return; task = std::move(this->tasks.front()); this->tasks.pop(); } task(); } }); } } template<class F> auto ThreadPool::enqueue(F&& f) -> std::future<decltype(f())> { using return_type = decltype(f()); auto task = std::make_shared<std::packaged_task<return_type()>>(std::forward<F>(f)); std::future<return_type> res = task->get_future(); { std::unique_lock<std::mutex> lock(queue_mutex); if (stop) throw std::runtime_error("enqueue on stopped ThreadPool"); tasks.emplace([task]() { (*task)(); }); } condition.notify_one(); return res; } ThreadPool::~ThreadPool() { { std::unique_lock<std::mutex> lock(queue_mutex); stop = true; } condition.notify_all(); for (std::thread &worker : workers) worker.join(); } int main() { ThreadPool pool(4); auto futureResult = pool.enqueue([] { return 42; }); std::cout << "Result: " << futureResult.get() << std::endl; return 0; } ``` When I run this code, the program hangs indefinitely on `futureResult.get()`, and I don't see any output or behavior messages. I tried adding print statements to check if the task is being executed, and it seems like the worker threads never get to that point. I verified that the thread pool is created correctly, and tasks are being enqueued, but it seems the condition variable might not be waking up the threads. Any ideas on what might be going wrong or what I could check to debug this further? Thanks for your help in advance! Thanks in advance! I'm coming from a different tech stack and learning C++.