Singleton Creation the Thread-safe Way

Listing 2: A common singleton implementation

//try1.h
class Singleton
{
public:
   static Singleton& instance();
   void show_state();

protected:
   Singleton();

private:
   static Singleton* _instance;
   int state;
};

Singleton* Singleton::_instance = NULL;

Singleton& Singleton::instance()
{
   if(!_instance) // Race condition exists here
      _instance = new Singleton;

   return *_instance;
}