C++ 11线程池 ThreadPool

线程池 ThreadPool

半同步半异步线程池(简略版)C++11实现,详细解析

同步队列

SynchronousQueue.hpp

#include <list>
#include <mutex>
#include <thread>
#include <condition_variable>
#include <iostream>
using namespace std;

template<typename T>
class SyncQueue
{
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
public:
	SyncQueue(int maxSize) :m_maxSize(maxSize), m_needStop(false){}
	void Put(const T& x)
	{
		Add(x);	
	}
	void Put(T&& x)
	{
		Add(std::forward<T>(x));
	}
	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)
		{
			return;
		}
		list = std::move( m_queue);
		m_notEmpty.notify_one();	
	}
	void Take(T& t)
	{
		std::unique_lock<std::mutex> locker(m_mutex);
		m_notEmpty.wait(locker, [this] {return m_needStop || NotEmpty(); });
		if (m_needStop)
			return;
		t = 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();
	}
	bool Empty()
	{
		std::lock_guard<std::mutex> locker(m_mutex);
		return  m_queue.empty();
	}
	bool Full()
	{
		std::lock_guard<std::mutex> locker(m_mutex);
		return  m_queue.size() == m_maxSize;
	}
	size_t Size()
	{
		std::lock_guard<std::mutex> locker(m_mutex);
		return  m_queue.size();
	}
	int Count()
	{
		return  m_queue.size();
	}
private:
	bool NotFull() const
	{
		bool full = (m_queue.size() >= m_maxSize);
		if(full)
		{
			cout << "缓冲区满了" << endl;
		}
		return !full;
	}
	bool NotEmpty() const
	{
		bool empty = m_queue.empty();
		if (empty)
			cout << "缓冲区空了,需要等待 IDP:"<<std::this_thread::get_id() << endl;
		return !empty;
	}
	template<typename  F>
	void Add(F&&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(std::forward<F>(x));
		m_notEmpty.notify_one();
	}
	
};

1. Take函数解析:

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)
		{
			return;
		}
		list = std::move( m_queue);
		m_notEmpty.notify_one();
		
	}

创建一个unique_lock获取mutex然后通过m_notEmpty等待判断式 ,{return m_needStop || NotEmpty(); }判断式由两个部分组成,一个是停止的标志,另一个是不为空的条件

• 当两个条件都不满足时,条件变量会释放mutex然后等待waiting条件满足直到其他线程通知notify_one()或者notify_all()
• 当满足m_needStop时,通过判断式结束函数
• 当满足NotEmpty()时,用一个队列将等待队列中的全部任务取出
  释放锁,并唤醒一个线程去添加任务

1. Add函数

template<typename  F>
	void Add(F&&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(std::forward<F>(x));
		m_notEmpty.notify_one();
	}

与上一个相似

• 如果满足条件,就执行以下逻辑,退出函数或者是添加新元素,然后唤醒取任务的线程

1. Stop()函数

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

Stop函数先获取mutex,然后将停止标志置为true,注意为了保证线程安全这里需要先获取锁,并将m_needStop标志为true再唤醒所有等待线程

线程池

一个完整的线程池包括三层

• 同步服务层
• 排队层
• 异步服务层

这也是一种生产者–消费者模式,同步层是生产者,不断将新任务丢到排队层中,因此线程池需要提供一个添加新任务的接口供生产者使用;

消费者是异步层,由线程池中与预先创建好的线程去处理同步队列中的任务;

排队层:同步队列,保证生产者,消费者对任务正常的访问,同时还要限制任务的数量,防止无限的任务被添加进来

除此之外,还要求用户能控制线程池的开启和停止,让我们在需要的时候开启/停止线程池

如下实现:

ThreadPool.hpp

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

constexpr  int MaxTaskCount = 100;

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

	ThreadPool(int numThreads = std::thread::hardware_concurrency()) :m_queue(MaxTaskCount)
	{
		Start(numThreads);
	}
	~ThreadPool()
	{
		//如果没有停止就主动停止线程池
		Stop();
	}
	void Stop()
	{
		std::call_once(m_flag, [this] {StopThreadGroup(); });
	}
	void AddTask(Task&& task)
	{
		m_queue.Put(std::forward<Task>(task));
	}
	void AddTask(const Task& task)
	{
		m_queue.Put(task);
	}
	
	void Start(int numThreads)
	{
		m_running = true;
		for (int i = 0; i<numThreads;i++)
		{
			m_threadgroup.push_back(std::make_shared<std::thread>(&ThreadPool::RunInThread, this));
		}
	}
	void RunInThread()
	{
		while (m_running)
		{
			std::list<Task> list;
			m_queue.Take(list);

			for (auto& task : list)
			{
				if (!m_running)
				{
					return;
				}
				task();
			}
		}
	}
	void StopThreadGroup()
	{
		m_queue.Stop();
		m_running = false;

		for (auto thread : m_threadgroup)
		{
			if (thread)
				thread->join();
			
		}
		m_threadgroup.clear();
	}

private:
	std::list<std::shared_ptr<std::thread>> m_threadgroup;   // 处理任务的线程组
	SyncQueue<Task> m_queue;                                  // 同步队列
	atomic_bool m_running;
	std::once_flag m_flag;


};

1. ThreadPool(int numThreads = std::thread::hardware_concurrency())构造函数用硬件支持的线程数初始化总线程数
   然后Start(numThreads)将m_running标志置为true,在线程池中放入numThreads个线程的指针
2. AddTask由测试程序向同步队列中添加任务(函数)
3. RunInThread()取出任务并执行

测试程序实现

main.cpp

#include "ThreadPool.hpp"
void TestThdPool()
{
	ThreadPool pool;
	pool.Start(2);
	std::thread thd1([&pool]
		{
			for (int i = 0; i < 10; ++i)
			{
				auto thdId = this_thread::get_id();
				pool.AddTask([thdId] {
					cout << "同步线程1的线程ID" << thdId << endl;
					});

			}
		});
	std::thread thd2([&pool]
		{
			for (int i = 0; i < 10; ++i)
			{
				auto thdId = this_thread::get_id();
				pool.AddTask([thdId]
					{
						cout << "同步层线程的线程ID:" << thdId << endl;
					});
			}
		});

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


int main()
{
	 
		TestThdPool();
	

}