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113 lines
3.1 KiB
113 lines
3.1 KiB
5 years ago
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#pragma once
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#include <vector>
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#include <queue>
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#include <memory>
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#include <thread>
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#include <mutex>
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#include <condition_variable>
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#include <future>
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#include <functional>
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#include <stdexcept>
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class ThreadPool {
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public:
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ThreadPool(size_t);
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template<class F, class... Args>
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auto enqueue(F&& f, Args&&... args)
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-> std::future<typename std::result_of<F(Args...)>::type>;
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~ThreadPool();
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bool has_running_tasks() {
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std::unique_lock<std::mutex> lock(running_tasks_mutex);
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return n_running_tasks > 0;
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}
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private:
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// need to keep track of threads so we can join them
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std::vector< std::thread > workers;
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// the task queue
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std::queue< std::function<void()> > tasks;
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int n_running_tasks;
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// synchronization
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std::mutex queue_mutex;
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std::mutex running_tasks_mutex;
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std::condition_variable condition;
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bool stop;
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};
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// the constructor just launches some amount of workers
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inline ThreadPool::ThreadPool(size_t threads)
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: n_running_tasks(0), stop(false)
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{
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for(size_t i = 0;i<threads;++i)
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workers.emplace_back(
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[this]
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{
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for(;;)
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{
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std::function<void()> task;
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{
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std::unique_lock<std::mutex> lock(this->queue_mutex);
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this->condition.wait(lock,
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[this]{ return this->stop || !this->tasks.empty(); });
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if(this->stop && this->tasks.empty())
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return;
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task = std::move(this->tasks.front());
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this->tasks.pop();
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}
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{
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std::unique_lock<std::mutex> lock(this->running_tasks_mutex);
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n_running_tasks++;
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}
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task();
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{
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std::unique_lock<std::mutex> lock(this->running_tasks_mutex);
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n_running_tasks--;
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}
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}
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}
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);
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}
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// add new work item to the pool
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template<class F, class... Args>
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auto ThreadPool::enqueue(F&& f, Args&&... args)
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-> std::future<typename std::result_of<F(Args...)>::type>
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{
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using return_type = typename std::result_of<F(Args...)>::type;
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auto task = std::make_shared< std::packaged_task<return_type()> >(
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std::bind(std::forward<F>(f), std::forward<Args>(args)...)
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);
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std::future<return_type> res = task->get_future();
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{
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std::unique_lock<std::mutex> lock(queue_mutex);
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// don't allow enqueueing after stopping the pool
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if(stop)
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throw std::runtime_error("enqueue on stopped ThreadPool");
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tasks.emplace([task](){ (*task)(); });
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}
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condition.notify_one();
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return res;
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}
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// the destructor joins all threads
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inline ThreadPool::~ThreadPool()
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{
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{
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std::unique_lock<std::mutex> lock(queue_mutex);
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stop = true;
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}
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condition.notify_all();
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for(std::thread &worker: workers)
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worker.join();
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}
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