线程池

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

class ThreadPool {
public:
    ThreadPool(size_t numThreads) {
        for (size_t i = 0; i < numThreads; ++i) {
            threads.emplace_back([this] {
                while (true) {
                    std::function<void()> task;
                    {
                        std::unique_lock<std::mutex> lock(this->queueMutex);
                        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();
                }
            });
        }
    }

    template<class F>
    void enqueue(F&& f) {
        {
            std::unique_lock<std::mutex> lock(queueMutex);
            tasks.emplace(std::forward<F>(f));
        }
        condition.notify_one();
    }

    ~ThreadPool() {
        {
            std::unique_lock<std::mutex> lock(queueMutex);
            stop = true;
        }
        condition.notify_all();
        for (std::thread& worker : threads) {
            worker.join();
        }
    }

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

int main() {
    ThreadPool pool(4);

    for (int i = 0; i < 8; ++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;
}

在Qt中，你可以使用QThreadPool类来实现线程池。QThreadPool管理着一组线程，可以用来执行一系列的任务。下面是一个简单的示例来演示如何使用QThreadPool：

#include <QCoreApplication>
#include <QRunnable>
#include <QThreadPool>
#include <QDebug>

class MyTask : public QRunnable {
public:
    void run() override {
        qDebug() << "Running a task in a thread";
    }
};

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);

    QThreadPool pool;
    pool.setMaxThreadCount(4); // 设置线程池中最大线程数

    MyTask task1, task2, task3;

    pool.start(&task1); // 将任务1添加到线程池中执行
    pool.start(&task2); // 将任务2添加到线程池中执行
    pool.start(&task3); // 将任务3添加到线程池中执行

    pool.waitForDone(); // 等待线程池中的所有任务执行完

    return a.exec();
}

在这个示例中，我们创建了一个QThreadPool对象pool，并设置了最大线程数为4。然后我们创建了三个自定义的任务类MyTask，并通过pool.start方法将这些任务添加到线程池中执行。最后调用pool.waitForDone方法等待线程池中的所有任务执行完。