class MySingleton{
public:
  static MySingleton* getInstance(){
    MySingleton* sin= instance.load(std::memory_order_acquire);
    if ( !sin ){
      std::lock_guard<std::mutex> myLock(myMutex);
      sin= instance.load(std::memory_order_relaxed);
      if( !sin ){
        sin= new MySingleton();
        instance.store(sin,std::memory_order_release);
      }
    }   
    return sin;
  }
private:
  MySingleton()= default;
  ~MySingleton()= default;
  MySingleton(const MySingleton&)= delete;
  MySingleton& operator=(const MySingleton&)= delete;

  static std::atomic<MySingleton*> instance;
  static std::mutex myMutex;
};