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134 lines
3.6 KiB
C++
134 lines
3.6 KiB
C++
// This code was modified from https://github.com/progschj/ThreadPool
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// The original License is copied below:
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//
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// Copyright (c) 2012 Jakob Progsch, Václav Zeman
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// This software is provided 'as-is', without any express or implied
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// warranty. In no event will the authors be held liable for any damages
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// arising from the use of this software.
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//
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// Permission is granted to anyone to use this software for any purpose,
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// including commercial applications, and to alter it and redistribute it
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// freely, subject to the following restrictions:
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//
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// 1. The origin of this software must not be misrepresented; you must not
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// claim that you wrote the original software. If you use this software
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// in a product, an acknowledgment in the product documentation would be
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// appreciated but is not required.
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//
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// 2. Altered source versions must be plainly marked as such, and must not be
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// misrepresented as being the original software.
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//
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// 3. This notice may not be removed or altered from any source
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// distribution.
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#pragma once
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#include <condition_variable>
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#include <functional>
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#include <future>
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#include <memory>
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#include <mutex>
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#include <queue>
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#include <stdexcept>
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#include <thread>
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#include <vector>
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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::invoke_result_t<F, Args...>>;
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void resize(size_t);
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~ThreadPool();
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private:
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void stop_and_wait();
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void start_threads(size_t);
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std::vector<std::thread> workers;
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std::queue<std::function<void()>> tasks;
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std::mutex queue_mutex;
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std::condition_variable condition;
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bool stop;
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};
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inline ThreadPool::ThreadPool(size_t threads) : stop(false) {
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start_threads(threads);
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}
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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::invoke_result_t<F, Args...>> {
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using return_type = typename std::invoke_result_t<F, Args...>;
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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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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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if (stop) {
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throw std::runtime_error(
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"[ThreadPool::enqueue] Not allowed on stopped ThreadPool");
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}
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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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inline void ThreadPool::resize(size_t threads) {
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if (workers.size() == threads) {
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return;
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}
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if (workers.size() > threads) {
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stop_and_wait();
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}
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start_threads(threads - workers.size());
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}
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inline ThreadPool::~ThreadPool() {
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stop_and_wait();
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}
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inline void ThreadPool::stop_and_wait() {
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// Stop the current threads and wait until they finish
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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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// Reset the member variables so that the threadpool is reusable
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stop = false;
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workers.clear();
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}
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inline void ThreadPool::start_threads(size_t threads) {
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for (size_t i = 0; i < threads; ++i) {
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workers.emplace_back([this] {
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for (;;) {
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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(
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lock, [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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task();
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}
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});
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}
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}
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