Singleton in multi-threaded environment

Question: How would you write a singleton in a multi-threaded environment?

In a singleton, there are two race conditions; one where the instance is created and the other when we access instance data. The method which creates the singleton instance must be made thread safe. Here is an example:

#include <memory> class MySingleton { static HANDLE s_Mutex; // Make the constructor and assignment operator private MySingleton(); MySingleton & operator =( const MySingleton &); public: static MySingleton& GetInstance(); }; // Create a mutex with default // security attributes, not-owned, HANDLE MySingleton::s_Mutex = ::CreateMutex( NULL, false, "MySingleton"); MySingleton & MySingleton::GetInstance() { static auto_ptr<MySingleton> s_Instance; if( !s_Instance ) { try { ::WaitForSingleObject( s_Mutex ); if( !s_Instance ) { s_Instance = new MySingleton(); } ::ReleaseMutex( s_Mutex ); return s_Instance; } catch(...) { ::ReleaseMutex( s_Mutex ); throw; } } };