C++11 实现线程池

线程池

在程序开始运行前创建多个线程这样，程序在运行时，只需要从线程池中拿来用就可以了．大大提高了程序运行效率。

1. 线程池中预先设置了多个线程。
2. 线程池中有一个任务队列，用于存储函数。
3. 线程池中有一个push任务的函数，讲需要在线程中调用的函数以及函数参数push到队列中。
4. 线程池中不断监听任务队列，利用信号量机制判断是否有任务到队列中。监听到任务则执行。

线程池的实现

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

class ThreadPool{
public:
    ThreadPool(int num) : stop(false)
    {
        for (int i = 0; i < num; i++)
        {
            threads.emplace_back([this](){
                while(true)
                {
                    std::unique_lock<std::mutex> lock(mtx);
                    cv.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;
        }
        cv.notify_all();
        for (auto& t : threads)
        {
            t.join();
        }
    }
    
    // not undersanding ...
    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(mtx);
            tasks.emplace(std::move(task));
        }
        cv.notify_one();
    }
    
private:
    bool stop;
    /* threads list*/
    std::vector<std::thread> threads;
    /* task list*/
    std::queue<std::function<void()>> tasks;
    
    std::mutex mtx;
    std::condition_variable cv;
};


void task(std::string name, int data)
{
    std::cout << "name : " << name << ", data : " << data << std::endl;
}

int main()
{
    ThreadPool pool(4);
    for(int i = 0; i < 10; i++)
    {
        pool.enqueue(task, "task", i);
    }
    return 0;
}

带有返回结果的线程池

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

class ThreadPool {
public:
    ThreadPool(size_t numThreads) : stop(false) {
        for (size_t i = 0; i < numThreads; ++i) {
            workers.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, class... Args>
    auto enqueue(F&& f, Args&&... args) -> std::future<decltype(f(args...))> {
        using return_type = decltype(f(args...));
        auto task = std::make_shared<std::packaged_task<return_type()>>(std::bind(std::forward<F>(f), std::forward<Args>(args)...));
        std::future<return_type> res = task->get_future();
        {
            std::unique_lock<std::mutex> lock(queueMutex);
            if (stop) {
                throw std::runtime_error("enqueue on stopped ThreadPool");
            }
            tasks.emplace([task]() { (*task)(); });
        }
        condition.notify_one();
        return res;
    }

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

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

// Example function to be executed in the thread pool
int add(int a, int b) {
    return a + b;
}

int main() {
    ThreadPool pool(4);

    // Enqueue tasks and get return values
    std::future<int> result1 = pool.enqueue(add, 2, 3);
    std::future<int> result2 = pool.enqueue(add, 5, 7);

    // Get the results
    std::cout << "Result1: " << result1.get() << std::endl;
    std::cout << "Result2: " << result2.get() << std::endl;

    return 0;
}

std::packaged_task 说明