Singleton模式

单线程singleton模式

#include <iostream>  
using namespace std;  

template <typename T>  
class Singleton  
{  
public:  
	static T* getInstance()  
	{  
		if( !instance )             
		{  
			instance = new T();
		}  
		return instance;  
	}  
private:  
	Singleton();  
	static T* instance;  
};  

template <typename T>  
T* Singleton<T>::instance = NULL;  

class Stu  
{  
public:  
	Stu(){
		cout<<"Stu"<<endl;
	}
};  

int main(void)  
{  
	Stu *s = Singleton<Stu>::getInstance();  
	Stu *s2 = Singleton<Stu>::getInstance();  

	return 0;  
}  

单线程下安全，但是多线程则不安全：

解决办法有三种手段：

1. 同步                                                    加锁
2. 急切创建  直接初始化                      static T* instance = new T();
3. double check                                   

   		if(m_instance == NULL)
   		{
   			m_Lock.Lock();
   
   			if(m_instance == NULL)
   			{
   
   				instance = new T();
   
   			}
   
   			m_Lock.UnLock();
   		}
    

   
   

#include <iostream>
#include <Windows.h>
using namespace std;  

class CLock
{
public:
	CLock()
	{
		::InitializeCriticalSection(&m_Section);
	}
	~CLock()
	{
		::DeleteCriticalSection(&m_Section);
	}

	void Lock()
	{
		::EnterCriticalSection(&m_Section);
	}

	void UnLock()
	{
		::LeaveCriticalSection(&m_Section);
	}
private:
	CRITICAL_SECTION m_Section;
};

template <typename T>  
class Singleton  
{  
public:  
	static T* getInstance()  
	{  
		if( NULL == instance )             
		{  
			m_Lock.Lock();
			if ( NULL == instance)
			{
				instance = new T();
			}	
			m_Lock.UnLock();
		}  
		return instance;  
	}  

	static void release()
	{
		if(instance)
		{
			delete instance;
			instance = NULL;
		}
	}
private:  
    Singleton();
	static CLock m_Lock;
	static T* instance;  
};  

template <typename T>  
T* Singleton<T>::instance = NULL;  

template <typename T>
CLock Singleton<T>::m_Lock;

class Stu  
{  
public:  
	Stu(){
		cout<<"Stu"<<endl;
	}
};  

int main(void)  
{  
	Stu *s = Singleton<Stu>::getInstance();  
	Stu *s2 = Singleton<Stu>::getInstance();  

	return 0;  
}