public void Run()
        {
            Console.WriteLine("Getting instance 1...");
            var instance1 = AppSingleton.GetInstance();

            Console.WriteLine("Done.");

            Console.WriteLine("Getting instance 2...");
            var instance2 = AppSingleton.GetInstance();

            Console.WriteLine("Done.");

            Console.WriteLine($"instance1 is the same object as instance2: {instance1 == instance2}");
        }
        public static AppSingleton GetInstance()
        {
            if (_singleInstance == null)
            {
                lock (_lockObject)
                {
                    if (_singleInstance == null)
                    {
                        _singleInstance = new AppSingleton();
                    }
                }
            }

            return(_singleInstance);
        }