Worker(ThreadPool &s) : pool(s) { }

void operator()();

ThreadPool &pool;

ThreadPool(size_t);

template<class T, class F>

std::future<T> enqueue(F f);

~ThreadPool();

friend class Worker;

// 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;

: stop(false)

{

for(size_t i = 0;i<threads;++i)

workers.push_back(std::thread(Worker(*this)));

{

// 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<T()> >(f);

std::future<T> res = task->get_future();

{

std::unique_lock<std::mutex> lock(queue_mutex);

tasks.push([task](){ (*task)(); });

}

condition.notify_one();

return res;