使用C++11 开发一个半同步半异步线程池

摘自：《深入应用C++11》第九章

实际中，主要有两种方法处理大量的并发任务，一种是一个请求由系统产生一个相应的处理请求的线程（一对一）

另外一种是系统预先生成一些用于处理请求的进程，当请求的任务来临时，先放入同步队列中，分配一个处理请求的进程去处理任务，

线程处理完任务后还可以重用，不会销毁，而是等待下次任务的到来。（一对多的线程池技术）

线程池技术，能避免大量线程的创建和销毁动作，节省资源，对于多核处理器，由于线程被分派配到多个cpu，会提高并行处理的效率。

线程池技术分为半同步半异步线程池和领导者追随者线程池，下面附上代码：

//SyncQueue.hpp
//同步队列，存放任务
#ifndef SYNCQUEUE_HPP
#define SYNCQUEUE_HPP

#include <list>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <utility>
#include <iostream>

template<typename T>
class SyncQueue
{
public:
    SyncQueue(int maxSize) : m_maxSize(maxSize),m_needStop(false){}

    void Put(const T& x)
    {
        std::unique_lock<std::mutex> locker(m_mutex);
        m_notFull.wait(locker,[this]{ return m_needStop || NotFull();});
        if(m_needStop)
            return;
        m_queue.push_back(x);
        m_notEmpty.notify_one();
    }

    void Take(std::list<T>& list)
    {
        std::unique_lock<std::mutex> locker(m_mutex);
        m_notEmpty.wait(locker,[this]{return m_needStop || NotEmpty();});
        if(m_needStop)
    
        list = std::move(m_queue);   //move semantics,avoid copy.
        m_notFull.notify_one();
    }

    void Take(T& x)
    {
        std::unique_lock<std::mutex> locker(m_mutex);
        m_notEmpty.wait(locker,[this]{return m_needStop || NotEmpty();});
        if(m_needStop)
            return;
        x=m_queue.front();
        m_queue.pop_front();
        m_notFull.notify_one();
    }

    void Stop()
    {
        {
            std::lock_guard<std::mutex> locker(m_mutex);
            m_needStop = true;
        }
        m_notFull.notify_all();
        m_notEmpty.notify_all();
    }

    std::size_t Size()
    {
        std::lock_guard<std::mutex> locker(m_mutex);
        return m_queue.size();
    }
private:
    bool NotFull()
    {
        bool full = m_queue.size() >= m_maxSize;
        if(full)
            std::cout << "the buffer is full,waiting...
";
        return !full;
    }
    bool NotEmpty()
    {
        bool empty = m_queue.empty();
        if(empty)
            std::cout << "the buffer is empty,waiting...
";
        return !empty;
    }
private:
    std::list<T> m_queue;
    std::mutex m_mutex;
    std::condition_variable m_notEmpty;
    std::condition_variable m_notFull;
    int m_maxSize;     
    bool m_needStop;   //stop flag
};

#endif // SYNC_QUEUE_HPP

//ThreadPool.hpp

#ifndef THREAD_POOL_HPP
#define THREAD_POOL_HPP

#include <list>
#include <thread>
#include <memory>
#include "SyncQueue.hpp"
#include <functional>
#include <atomic>

const int MaxTaskCount = 100;

class ThreadPool
{
public:
    using Task = std::function<void()>; 

    ThreadPool(int numThreads) : 
        m_taskQueue(MaxTaskCount)
    {
        Start(numThreads);
    }

    ~ThreadPool(){ Stop();};
    void Stop()
    {
        std::call_once(m_once_flag,[this]{StopThreadGroup();});
    }

    void AddTask(const Task& task)
    {
        m_taskQueue.Put(task);
    }

    std::size_t SyncQueueSize()
    {
        return m_taskQueue.Size();
    }
private:
    void Start(int numThreads)
    {
        m_running = true;

        for(int i = 0;i < numThreads;++i)
        {
            m_threadGrop.push_back(std::make_shared<std::thread>(&ThreadPool::RunInThread,this));
        }

    }

    void RunInThread()
    {
        while(m_running)
        {
            std::list<Task> list;
            m_taskQueue.Take(list);
            for(auto& task : list)
            {
                if(!m_running)
                    return;

                task();
            }
        }
        return;
    }

    void StopThreadGroup()
    {
        m_taskQueue.Stop();
        m_running = false;
        for(auto thread : m_threadGrop)
        {
            if(thread)
                thread->join();
        }    
        m_threadGrop.clear();
    }
private:
    std::list<std::shared_ptr<std::thread>> m_threadGrop;   //thread group
    SyncQueue<Task> m_taskQueue;
    std::atomic_bool m_running;
    std::once_flag m_once_flag;
};

#endif // THREAD_POOL_HPP

测试：

#include "ThreadPool.hpp"
#include <thread>
#include <iostream>
#include <chrono>
#include <functional>
int main()
{
    ThreadPool pool(4); //create two threads to handle tasks
    
    std::thread thd1([&pool]{
        for(int i = 0;i < 10;i++)
        {
            auto thdId = std::this_thread::get_id();

            pool.AddTask([thdId]{
                std::cout<<"thdID1: "<< thdId << std::endl;
            });
        }
    });

    std::thread thd2([&pool]{
        for(int i = 0;i < 10;i++)
        {
            auto thdID = std::this_thread::get_id();

            pool.AddTask([thdID]{
                std::cout << "thdID2: " << thdID << std::endl;
            });
        }
    });

    thd1.join();
    thd2.join();
    std::this_thread::sleep_for(std::chrono::seconds(2));
    pool.Stop();
    return 0;
}