C++ 多线程笔记4

Tip

std::thread::hardware_concurrency() 返回 CPU 线程数，可作为线程池默认大小。

时间计数代码

//时间计数 us微秒 = micro 
auto t0 = std::chrono::steady_clock::now();
//代码
auto ms = std::chrono::duration<double, std::milli>(
std::chrono::steady_clock::now() - t0).count();
std::cout << "全部任务耗时 " << ms << " ms\n";

#include <iostream>
#include <thread>
#include <condition_variable>
#include <queue>
#include <vector>
#include <functional>
#include <atomic>
#include <mutex>

class ThreadPool {
private:
	std::mutex mtx;
	std::condition_variable condition;
	std::queue<std::function<void()>> tasks;
	std::atomic<bool> stop;
	std::vector<std::thread> threads;

	ThreadPool(const ThreadPool&) = delete;
	ThreadPool& operator=(const ThreadPool&) = delete;
	ThreadPool(int num_threads);

public:
	static ThreadPool& SetThreadPool(int num_threads) {
		static ThreadPool threadpool(num_threads);
		return threadpool;
	}

	~ThreadPool() {
		{
			std::lock_guard<std::mutex> lock(mtx);
			stop = true;
		}
		condition.notify_all();
		for (auto& t : threads) {
			t.join();
		}
	}
	template<typename F, typename... Args> void enqueue(F&& f, Args&&... args) {
		std::function<void()> task = std::bind(std::forward<F>(f), std::forward<Args>(args)...);
		if (stop) throw std::runtime_error("enqueue on stopped ThreadPool");
		{
			std::lock_guard<std::mutex> lock(mtx);
			tasks.emplace(std::move(task));
		}
		condition.notify_one();
	}
};

ThreadPool::ThreadPool(int num_threads) : stop{ false } {
	for (int i = 0; i < num_threads; i++) {
		threads.emplace_back([this]() {
			while (true)
			{
				std::unique_lock<std::mutex> lock(mtx);
				condition.wait(lock, [this]() { return !tasks.empty() || stop; });
				if (stop && tasks.empty()) return;
				std::function<void()> task(std::move(tasks.front()));
				tasks.pop();
				lock.unlock();
				task();
			}
			});
	}
}

int main() {
	ThreadPool& threadpool = ThreadPool::SetThreadPool(std::thread::hardware_concurrency());
	for (int i = 0; i < 500; i++) {
		threadpool.enqueue([i]() {
			std::cout << "task: " << i << " is running" << "\n";
			std::this_thread::sleep_for(std::chrono::milliseconds(10));
			std::cout << "task: " << i << " is done" << std::endl;
			});
	}

	return 0;
}