8. C++11 跨平台线程池

跨平台线程池实现

它使用 C++11 标准库中的 std::thread、std::mutex、std::condition_variable、std::function 和 std::queue 等组件实现。

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

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

~ThreadPool() {
    {
        std::unique_lock<std::mutex> lock(mutex);
        stop = true;
    }
    condition.notify_all();
    for (std::thread& thread : threads) {
        thread.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)...));
    {
        std::unique_lock<std::mutex> lock(mutex);
        tasks.emplace(std::move(task));
    }
    condition.notify_one();
}

private:
std::vector<std::thread> threads;
std::queue<std::function<void()>> tasks;
std::mutex mutex;
std::condition_variable condition;
bool stop;
};

int main() {
    ThreadPool pool(4);
    for (int i = 0; i < 8; ++i) {
        pool.enqueue([i] {
            std::cout << "Task " << i << " is running in thread " << std::this_thread::get_id() << std::endl;
            std::this_thread::sleep_for(std::chrono::seconds(1));
            std::cout << "Task " << i << " is done" << std::endl;
        });
    }
    return 0;
}

在这个示例中，我们同样定义了一个 ThreadPool 类，并且在构造函数中创建了指定数目的线程。在每个线程中，我们不断地从任务队列中获取任务并执行，直到线程池被停止。在 enqueue() 函数中，我们将任务封装成一个 std::function 对象，并将它添加到任务队列中。在 ThreadPool 的析构函数中，我们等待所有线程执行完成后再停止所有线程。

在主函数中，我们创建了一个 ThreadPool 对象，并向任务队列中添加了 8 个任务。每个任务会输出一些信息，并且在执行完后等待 1 秒钟。由于线程池中有 4 个线程，因此这 8 个任务会被分配到不同的线程中执行。在任务执行完成后，程序会退出。

#include <iostream>
#include <thread>
#include <mutex>
#include <string>
#include <condition_variable>
#include <queue>
#include <vector>
#include <functional>
class ThreadPool {
public:
	ThreadPool(int numThreads) :stop(false) {
		for (int i = 0; i < numThreads; i++) {
			threads.emplace_back([this] {
				while (1) {
					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();
				}
				});
		}
	}

	~ThreadPool() {
		{
			std::unique_lock<std::mutex> lock(mtx);
			stop = true;
		}
		

		condition.notify_all();
		for (auto& t : threads) {
			t.join();
		}
	}
	template<class F, class... Args>//函数模板里右值引用是万能引用
	void enqueue(F&& f, Args&&... args) {
		std::function<void()> task = 
			std::bind(std::forward<F>(f), std::forward<Args>(args)...);
		{
			std::unique_lock<std::mutex> lock(mtx);
			tasks.emplace(std::move(task));
		}
			condition.notify_one();
		
	}


private:
	std::vector<std::thread> threads;
	std::queue<std::function<void()>> tasks;

	std::mutex mtx;
	std::condition_variable condition;

	bool stop;

};

int main()
{
	ThreadPool pool(4);

	for (int i = 0; i < 10; i++) {
		pool.enqueue([i] {
			std::cout << "task : " << i << " is running" << std::endl;
			std::this_thread::sleep_for(std::chrono::seconds(1));
			std::cout << "task : " << i << " is done" << std::endl;
			});
	}
	return 0;
}