单例设计模式实例

#include "pch.h"
#include <iostream>
#include<list>
#include<mutex>

using namespace std;
std::mutex Mymutex;
//单例设计模式实例：
class MyCAS
{
private:
	static MyCAS *m_instance;
	MyCAS()
	{
	
	}
public:
	static MyCAS*  GetInstance()//多线程只读数据不需要加锁
	{
		if (m_instance == NULL)  //双重否定提高效率
		{
		    std::unique_lock<std::mutex> my_lock(Mymutex); //自动加锁
			if (m_instance == NULL)
			{
				m_instance = new MyCAS();
				static M_huishou m_hs;
				cout << "m_instance 被new" << endl;
			}
			
		}
		return m_instance;
	}
	MyCAS* print()
	{
		MyCAS* m = new MyCAS;
		return m;
	
	}
	class M_huishou
	{
	public: 
		~M_huishou()
		{
			if(MyCAS::m_instance)
			{
				delete MyCAS::m_instance;
				MyCAS::m_instance = NULL;
			}
		}
	};
};

 MyCAS * MyCAS::m_instance=NULL;  //静态成员变量初始化
 void func()
 {
	 MyCAS* m = MyCAS::GetInstance();
 }
int main()
{
	//MyCAS m;  //构造函数私有，不能直接实例对象
	//MyCAS* m1 = MyCAS::GetInstance();
	//MyCAS* m2 = MyCAS::GetInstance();
	std::thread my_thread1(func);
	std::thread my_thread2(func);
	my_thread1.join();
	my_thread2.join();

	return 0;
}