实现要点

  • 任务队列：使用 std::function 来包装任务，通过完美转发传递参数实现类型保留
  • 线程管理：初始化一组工作线程循环获取任务，当线程池不再被需要时，安全停止所有线程
  • 同步机制：使用互斥量保护任务队列，使用条件变量来通知工作线程有任务可执行或停止工作
  • 结果返回：使用 std::packaged_task 来包装任务，使用 std::future 来获取任务结果

代码：

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#include <iostream>
#include <queue>
#include <vector>
#include <array>
#include <thread>
#include <future>
#include <mutex>
#include <condition_variable>
#include <functional>
#include <memory>

class ThreadPool
{
private:
    std::vector<std::thread> m_threads;
    std::queue<std::function<void()>> m_tasks;
    std::mutex m_mutex;
    std::condition_variable m_condition;
    uint16_t m_threads_num;
    bool m_stop;

public:
    ThreadPool(int _threadNum) : m_threads_num(_threadNum), m_stop(false)
    {
        std::cout << "Thread pool constructing..." << std::endl;
        for (size_t i = 0; i < m_threads_num; i++)
        {
            m_threads.emplace_back([this]()
                                   {
                                    while (true)
                                    {
                                        std::function<void()> task;
                                        {
                                            std::unique_lock<std::mutex> lock(m_mutex);
                                            m_condition.wait(lock, [this]() { return !m_tasks.empty() || m_stop; });
                                            if (m_stop && m_tasks.empty())
                                            {
                                                return;
                                            }
                                            task = std::move(m_tasks.front());
                                            m_tasks.pop();
                                        }
                                        task();
                                    } });
        }
    }

    template <typename F, typename... Args>
    std::future<std::result_of_t<F(Args...)>> addTask(F &&_task, Args &&..._args)
    {
        using return_type = std::result_of_t<F(Args...)>;
        auto task = std::make_shared<std::packaged_task<return_type()>>(
            std::bind(std::forward<F>(_task), std::forward<Args>(_args)...));

        {
            std::lock_guard<std::mutex> lock(m_mutex);
            m_tasks.emplace([task]()
                            { (*task)(); });
        }
        std::future<return_type> future = task->get_future();
        return future;
    }

    void stop()
    {
        {
            std::unique_lock<std::mutex> lock(m_mutex);
            m_stop = true;
        }
        m_condition.notify_all();
    }

    ~ThreadPool()
    {
        stop();

        for (auto &thread : m_threads)
        {
            if (thread.joinable())
                thread.join();
        }
        std::cout << "Thread pool destructed." << std::endl;
    }
};

int calculate(const int &n)
{
    std::cout << "Task: " << n << " calculating: " << n << " * " << n << std::endl;
    return n * n;
}

int main()
{
    ThreadPool pool(4);

    std::array<std::future<int>, 10> futures;
    for (int i = 0; i < 10; i++)
    {
        futures[i] = pool.addTask(calculate, i);
    }

    for (int i = 0; i < 10; i++)
    {
        std::cout << "Calculate result: " << futures[i].get() << std::endl;
    }

    return 0;
}