单例实现

 

#pragma once
#include <Windows.h>
#include <memory>
using namespace std;
class CResGuard {
public:
   CResGuard()  { m_lGrdCnt = 0; InitializeCriticalSection(&m_cs); }
   ~CResGuard() { DeleteCriticalSection(&m_cs); }
   // IsGuarded is used for debugging
   BOOL IsGuarded() const { return(m_lGrdCnt > 0); }
public:
   class CGuard {
   public:
      CGuard(CResGuard& rg) : m_rg(rg) { m_rg.Guard(); };
      ~CGuard() { m_rg.Unguard(); }
   private:
      CResGuard& m_rg;
   };

private:
   void Guard()   { EnterCriticalSection(&m_cs); m_lGrdCnt++; }
   void Unguard() { m_lGrdCnt--; LeaveCriticalSection(&m_cs); }
   // Guard/Unguard can only be accessed by the nested CGuard class.
   friend class CResGuard::CGuard;
private:
   CRITICAL_SECTION m_cs;
   long m_lGrdCnt;   // # of EnterCriticalSection calls
};

template <class T>
class Singleton
{
public:
       static inline T* instance();
private:
       Singleton(void){}
       ~Singleton(void){}
       Singleton(const Singleton&){}
       Singleton & operator= (const Singleton &){}
       static auto_ptr<T> _instance;
       static CResGuard _rs;
};
template <class T>
auto_ptr<T> Singleton<T>::_instance;
template <class T>
CResGuard Singleton<T>::_rs;
template <class T>
 inline T* Singleton<T>::instance()
{
      if( 0 == _instance.get() )
       {
            CResGuard::CGuard gd(_rs);
             if( 0== _instance.get())
              {
                  _instance.reset ( new T);
              }
       }
       return _instance.get();
}

//Class that will implement the singleton mode,
//must use the macro in it's delare file
#define DECLARE_SINGLETON_CLASS(type)\
       friend class auto_ptr<type>;\
       friend class Singleton<type>;