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// https://github.com/progschj/ThreadPool/blob/master/ThreadPool.h
//
// modified so that a thread_id integer in [0..nb_threads] is passed to each task
//
#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 ThreadPool {
public:
ThreadPool(size_t);
template<class F, class... Args>
auto enqueue(F&& f, Args&&... args)
-> std::future<typename std::result_of<F(int, Args...)>::type>;
//~ThreadPool();
void join();
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(int)> > tasks;
// synchronization
std::mutex queue_mutex;
std::condition_variable condition;
bool stop;
};
// the constructor just launches some amount of workers
inline ThreadPool::ThreadPool(size_t threads)
: stop(false)
{
for(size_t thread_id = 0; thread_id<threads; ++ thread_id)
workers.emplace_back(
[this, thread_id]
{
for(;;)
{
std::function<void(int)> 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(thread_id);
}
}
);
}
// add new work item to the pool
template<class F, class... Args>
auto ThreadPool::enqueue(F&& f, Args&&... args)
-> std::future<typename std::result_of<F(int, Args...)>::type>
{
using return_type = typename std::result_of<F(int, Args...)>::type;
auto task = std::make_shared< std::packaged_task<return_type(int)> >(
std::bind(std::forward<F>(f), placeholders::_1, std::forward<Args>(args)...)
);
std::future<return_type> res = task->get_future();
{
std::unique_lock<std::mutex> lock(queue_mutex);
// don't allow enqueueing after stopping the pool
if(stop)
throw std::runtime_error("enqueue on stopped ThreadPool");
tasks.emplace([task](int thread_id){ (*task)(thread_id); });
}
condition.notify_one();
return res;
}
// the destructor joins all threads
// rayan: slightly modified, now explicit join
void ThreadPool::join()
{
{
std::unique_lock<std::mutex> lock(queue_mutex);
stop = true;
}
condition.notify_all();
for(std::thread &worker: workers)
worker.join();
}
#endif
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