c++多线程（十七） - std::mutex与windows临界区

谁借莪１个温暖的怀抱￠ 2022-02-05 01:09 385阅读 0赞

### 1.std::mutex ###

#include "stdafx.h"
    #include<iostream>
    #include<thread>
    #include<mutex>
    #include<list>
    using namespace std;
    
    //lock()和unlock()要成对使用。
    //分析需要保护的代码段
    class MsgManage
    {
    public:
    	MsgManage() {}
    	~MsgManage() {}
    	void InMsg()
    	{
    		for (int i = 0; i < 10000; i++)
    		{
    			cout << "插入元素: " << i << endl;
    			myMutex.lock();
    			myList.push_back(i);
    			myMutex.unlock();
    		}
    	}
    
    	bool outMsgProc(int &num)
    	{
    		myMutex.lock();
    		if (!myList.empty())
    		{
    			num = myList.front();
    			myList.pop_front();
    			myMutex.unlock();
    			return true;
    		}
    		myMutex.unlock();
    		return false;
    	}
    
    	void OutMsg()
    	{
    		for (int i = 0; i < 10000; i++)
    		{
    			int num;
    			bool result = outMsgProc(num);
    			if (result)
    			{
    				cout << "移除元素: " << num << endl;
    			}
    			else
    			{
    				cout << "消息队列为空" << endl;
    			}
    		}
    	}
    private:
    	list<int> myList;
    	mutex myMutex;
    };
    
    int main()
    {
    	MsgManage manage;
    	thread outMsg(&MsgManage::OutMsg, &manage);
    	thread inMsg(&MsgManage::InMsg, &manage);
    	inMsg.join();
    	outMsg.join();
    
    	return 0;
    }

### 2.windows临界区 ###

#include<iostream>
    #include<thread>
    #include<list>
    #include<windows.h>
    using namespace std;
    class MsgManage
    {
    public:
    	MsgManage()
    	{
    		InitializeCriticalSection(&myWInsec);//初始化windows临界区
    	}
    	~MsgManage() {}
    	void InMsg()
    	{
    		for (int i = 0; i < 10000; i++)
    		{
    			cout << "插入元素: " << i << endl;
    			EnterCriticalSection(&myWInsec); //进入临界区
    			myList.push_back(i);
    			LeaveCriticalSection(&myWInsec); //离开临界区		
    		}
    	}
    	bool outMsgProc(int &num)
    	{
    		EnterCriticalSection(&myWInsec); //进入临界区
    		if (!myList.empty())
    		{
    			num = myList.front();
    			myList.pop_front();
    			LeaveCriticalSection(&myWInsec); //离开临界区
    			return true;
    		}
    		LeaveCriticalSection(&myWInsec); //离开临界区
    		return false;
    	}
    
    	void OutMsg()
    	{
    		for (int i = 0; i < 10000; i++)
    		{
    			int num;
    			bool result = outMsgProc(num);
    			if (result)
    			{
    				cout << "移除元素: " << num << endl;
    			}
    			else
    			{
    				cout << "消息队列为空" << endl;
    			}
    		}
    	}
    private:
    	list<int> myList;
    	CRITICAL_SECTION myWInsec; //windows临界区
    };
    
    int main()
    {
    	MsgManage manage;
    	thread outMsg(&MsgManage::OutMsg, &manage);
    	thread inMsg(&MsgManage::InMsg, &manage);
    	inMsg.join();
    	outMsg.join();
    	return 0;
    }

### 3.综合 ###

#include<iostream>
    #include<thread>
    #include<mutex>
    #include<list>
    #include<windows.h>
    using namespace std;
    
    #define _WINDOWSJQ_
    class MsgManage
    {
    public:
    	MsgManage()
    	{
    #ifdef _WINDOWSJQ_
    		InitializeCriticalSection(&myWInsec);//初始化windows临界区
    #endif 
    	}
    	~MsgManage() {}
    	void InMsg()
    	{
    		for (int i = 0; i < 10000; i++)
    		{
    			cout << "插入元素: " << i << endl;
    #ifdef _WINDOWSJQ_
    			EnterCriticalSection(&myWInsec); //进入临界区
    			myList.push_back(i);
    			LeaveCriticalSection(&myWInsec); //离开临界区
    #else
    			myMutex.lock();
    			myList.push_back(i);
    			myMutex.unlock();
    #endif 		
    		}
    	}
    
    	bool outMsgProc(int &num)
    	{
    #ifdef _WINDOWSJQ_
    		EnterCriticalSection(&myWInsec); //进入临界区
    		if (!myList.empty())
    		{
    			num = myList.front();
    			myList.pop_front();
    			LeaveCriticalSection(&myWInsec); //离开临界区
    			return true;
    		}
    		LeaveCriticalSection(&myWInsec); //离开临界区
    #else
    		myMutex.lock();
    		if (!myList.empty())
    		{
    			num = myList.front();
    			myList.pop_front();
    			myMutex.unlock();
    			return true;
    		}
    		myMutex.unlock();
    #endif
    		return false;
    	}
    
    	void OutMsg()
    	{
    		for (int i = 0; i < 10000; i++)
    		{
    			int num;
    			bool result = outMsgProc(num);
    			if (result)
    			{
    				cout << "移除元素: " << num << endl;
    			}
    			else
    			{
    				cout << "消息队列为空" << endl;
    			}
    		}
    	}
    private:
    	list<int> myList;
    	mutex myMutex;
    #ifdef _WINDOWSJQ_
    	CRITICAL_SECTION myWInsec; //windows临界区
    #endif 
    };
    
    int main()
    {
    	MsgManage manage;
    	thread outMsg(&MsgManage::OutMsg, &manage);
    	thread inMsg(&MsgManage::InMsg, &manage);
    	inMsg.join();
    	outMsg.join();
    	return 0;
    }

### 4.总结 ###

通过对windows临界区和mutex实例测试，总结如下差异：

*  同一个线程，相同的临界区，允许多次进入。
 *  同一个线程，相同的mutex对象，不允许多次lock()/unlock()