线程池

#include <iostream>
#include <vector>
#include <chrono>
#include <functional>
#include "ThreadPool.h"
#include <omp.h>

class CA
{
    int a = 1;
    int b = 2;
public:
    int Max(int a, int b)
    {
        return a > b ? a : b;
    }

#if 0
    double Max(int a)
    {
        return a;
    }
#endif
    int Sum(int a, int b)
    {
        return a + b;
    }
};


int main()
{

    ThreadPool pool(4);
    std::vector< std::future<int> > results;

    for (int i = 0; i < 16; ++i) {
        results.emplace_back(
            pool.enqueue([i] {
        //    std::cout << "hello " << i << std::endl;
        //    std::this_thread::sleep_for(std::chrono::seconds(1));
            return i*i;
        })
            );
    }
    for (auto && result : results){
        //std::cout << result.get() << ‘ ‘;
        std::cout <<"sync"<< ‘\n‘;
    }//同步：要等这里结束，才能往下执行，
    std::cout << "~~main~~" << std::endl;

    //成员函数不能有重名的（重载）。
    CA testA;

    //mem_fn
    std::future<int> fe = pool.enqueue(std::mem_fn(&CA::Max), testA, 3, 99999);
    //bind
    using namespace std::placeholders;
    std::future<int> fl = pool.enqueue(std::bind(&CA::Sum,&testA,_1,_2),3,99);

    std::cout << fl.get()  << std::endl;
    std::cout << fe.get()  << std::endl;
    return 0;
}

#ifndef THREAD_POOL_H
#define THREAD_POOL_H

#include <vector>
#include <queue>
#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <stdexcept>
#include <stdio.h>
#include <chrono>             // std::chrono::seconds


//线程池线程空闲自动退出时间间隔 ,5分钟
const int  THREAD_WAIT_TIME_OUT = 10;  //10 s



class ThreadPool {
public:
    ThreadPool(size_t);
    template<class F, class... Args>
    auto enqueue(F&& f, Args&&... args)
        ->//std::future<typename std::result_of<F(Args...)>::type>;
        //std::future < decltype(f(std::forward<Args>(args...))) > ;
    std::future < decltype(f(args...)) > ;
    void threadFun();
    ~ThreadPool();
    
private:
    // need to keep track of threads so we can join them
    std::vector< std::thread > workers;
    // the task queue
    std::queue< std::function<void()> > tasks;

    // synchronization
    std::mutex queue_mutex;
    std::condition_variable condition;
    bool stop;
};

// the constructor just launches some amount of workers
inline ThreadPool::ThreadPool(size_t threads)
    : stop(false)
{
    for (size_t i = 0; i<threads; ++i)
        workers.emplace_back(&ThreadPool::threadFun, this);
}

// add new work item to the pool
template<class F, class... Args>
auto ThreadPool::enqueue(F&& f, Args&&... args)
->//std::future<decltype(f(std::forward<Args>(args...)))>
//std::future<typename std::result_of<F(Args...)>::type>
std::future<decltype(f(args...))>
{
    //  using return_type = typename std::result_of<F(Args...)>::type;
    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(queue_mutex);
        // don‘t allow enqueueing after stopping the pool
        if (stop)
            throw std::runtime_error("enqueue on stopped ThreadPool");
        tasks.emplace([task]{ (*task)(); });
        //tasks.emplace([task]{ std::move(*task)(); });
    }
    condition.notify_one();
    return res;
}

void ThreadPool::threadFun()  {
    for (;;)
    {
        std::function<void()> task;
        {
            //std::unique_lock<std::mutex> lock(this->queue_mutex);
            std::unique_lock<std::mutex> lock(queue_mutex);
            //当条件为假的时候，才阻塞
            //同时为假才阻塞，stop为false ,并且任务为空
            this->condition.wait(lock,
                [this]{ return this->stop || !this->tasks.empty(); });

            if (this->stop && this->tasks.empty())
            {
                printf("@@--%d--@@\n", std::this_thread::get_id());
                if (this->condition.wait_for(lock, std::chrono::seconds(THREAD_WAIT_TIME_OUT)) == std::cv_status::timeout)
                    // printf("@@--%d--@@\n",std::this_thread::get_id());
                    break;
                else
                    continue;
            }

            task = std::move(this->tasks.front());
            this->tasks.pop();
        }
        task();
    }
}

// the destructor joins all threads
inline ThreadPool::~ThreadPool()
{
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        stop = true;
    }
    condition.notify_all();
    for (std::thread &worker : workers)
        worker.join();
}

#endif