[Java知识库]C++ 线程池

转载：醍醐灌顶全方位击破C++线程池及异步处理 - 知乎 (zhihu.com)

重点：

转载的代码有点乱，他有两种方法，只测试了第二种方法。

代码是看了，但无法验证这个线程池的暂停是否有效。等后续再想想，测试暂停的有效性。

Threadpool.h

#pragma once

#include <functional>
#include <thread>
#include <queue>
#include <condition_variable>
#include <future>
using namespace std;
using Task = function<void()>;

class ThreadPool
{
public:
    ThreadPool(size_t size = 4);
	~ThreadPool();
public:
    template<typename T, typename...Args>
    auto Commit(T&& t, Args&&...args)->future<decltype(t(args...))>
    {
        if (m_stop.load())
        {
            throw runtime_error("task has closed commit");
        }
        using ResType = decltype(t(args...));
        auto task = make_shared<packaged_task<ResType()>>(
            bind(forward<T>(t), forward<Args>(args)...));

        unique_lock<mutex> lock(mu);
        m_tasks.emplace([task]() {
            (*task)();
            });
        m_cv.notify_all(); //唤醒等待线程
        future<ResType> fu = task->get_future();
        return fu;
    }
public:
	void ShutDown(); //停止任务提交
	void Restart(); //重启任务提交
	
private:
	Task GetOneTask();//获取一个待执行的task
	void Schedual();  //任务调度
private:
	vector<thread> m_pool;
	mutex mu;
	queue<Task> m_tasks;
	condition_variable m_cv;
	atomic<bool> m_stop;
};

ThreadPool.cpp

#include "ThreadPool.h"
#include <future>

ThreadPool::ThreadPool(size_t size) :m_stop{false}
{
    size = size < 1 ? 1 : size;
    for (size_t i=0;i<size;++i)
    {
        m_pool.emplace_back(&ThreadPool::Schedual, this);
    }
}

ThreadPool::~ThreadPool()
{
    for (auto&t:m_pool)
    {
        t.detach(); //让线程自身自灭
        //t.join(); //等任务结束，前提：线程一定会执行完
    }
}

void ThreadPool::ShutDown()
{
    m_stop.store(true);//对内存进行访问memory_order_seq_cst,采用store
}

void ThreadPool::Restart()
{
    m_stop.store(false);//对内存进行访问memory_order_seq_cst,采用store
}



Task ThreadPool::GetOneTask()
{
    unique_lock<mutex> lock(mu);
    m_cv.wait(lock, [this] {return !m_tasks.empty(); });
    Task task(move(m_tasks.front()));
    m_tasks.pop();
    return task;
}

void ThreadPool::Schedual()
{
    while (true)
    {
        if (Task task =GetOneTask())
        {
            task();
        }
        else
        {
            return;   //结束
        }
    }
}

Test.cpp

// Test.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

#include <iostream>
#include <future>
#include "ThreadPool.h"
using namespace std;

void fun()
{
    for (int i = 0; i < 100000; ++i)
    {
        cout << "hello"<<i << endl;
    }
   
}

struct Gan
{
    int operator()() {
        cout << "hello,gan" << endl;
        return 42;
    }
};

int main() {
	try
	{
        ThreadPool task(10);
        future<void> ff = task.Commit(fun);
        future<int> fg = task.Commit(Gan());
        future<string> fs = task.Commit([]()->string {
            return "hello,fs";
            });
       
        task.ShutDown();
        ff.get();
        
        cout << "fg.get : " << fg.get ()<< endl;
        this_thread::sleep_for(chrono::seconds(5));
        task.Restart(); //重启任务
        cout << "end " << endl;
        return 0;
	}
	catch (const std::exception& e)
	{
        cout << "soming is wrong "<< e.what() << endl;
	}
    return 0;
}