private static void PrintS2()
        {
            SingletonThreadSafety s2 = SingletonThreadSafety.GetInstance;

            s2.PrintDetails("From Singleton Thread Safety S2");
        }
        //SINGLETON THREAD SAFETY
        private static void PrintS1()
        {
            SingletonThreadSafety s1 = SingletonThreadSafety.GetInstance;

            s1.PrintDetails("From Singleton Thread Safety S1");
        }