mutex myMutex;

 class MySingleton{
 public:
   static MySingleton& getInstance(){
     lock_guard<mutex> myLock(myMutex);
     if( !instance ) instance= new MySingleton();
     return *instance;
   }
 private:
   MySingleton()= default;
   ~MySingleton()= default;
   MySingleton(const MySingleton&)= delete;
   MySingleton& operator=(const MySingleton&)= delete;
   static MySingleton* instance;
 };
 MySingleton* MySingleton::instance= nullptr;