thread_pool.h

#ifndef THREAD_POOL_H
#define THREAD_POOL_H

#include <vector>
#include <queue>
#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <stdexcept>

class thread_pool {
public:
    thread_pool(size_t);
    template<class F, class... Args>
    auto enqueue_task(F&& f, Args&&... args) 
        -> std::future<typename std::result_of<F(Args...)>::type>;
    ~thread_pool();
private:
    // need to keep track of threads so we can join them
    std::vector< std::thread > workers;
    // the task queue
    std::queue< std::function<void()> > tasks;
    
    // synchronization
    std::mutex queue_mutex;
    std::condition_variable condition;
    bool stop;
};
 
// add new work task to the pool
template<class F, class... Args>
auto thread_pool::enqueue_task(F&& f, Args&&... args) 
    -> std::future<typename std::result_of<F(Args...)>::type>
{
    typedef typename std::result_of<F(Args...)>::type return_type;
    
    // don't allow enqueueing after stopping the pool
    if (stop)
        throw std::runtime_error("enqueue on stopped ThreadPool");

    auto task = std::make_shared< std::packaged_task<return_type()> >(
            std::bind(std::forward<F>(f), std::forward<Args>(args)...)
        );
        
    std::future<return_type> res = task->get_future();
	
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        tasks.push([task](){ (*task)(); });
    }
	
    condition.notify_one();
    return res;
}

#endif