static void Main(string[] args)
        {
            //方法1:非多线程下
            //for (int i = 0; i < 10; i++)
            //{
            //    SingletonClass singleton = SingletonClass.GetInstance();
            //    singleton.Show();
            //}

            //方法2:多线程下
            //for (int i = 0; i < 5; i++)
            //{
            //    Task.Run(() =>
            //    {
            //        SingletonClass singleton = SingletonClass.GetInstance();
            //        singleton.Show();
            //    });
            //}

            //方法3:多线程下使用静态构造函数
            for (int i = 0; i < 5; i++)
            {
                Task.Run(() =>
                {
                    SingletonSecClass singletonSec = SingletonSecClass.GetInstance();
                    singletonSec.Show();
                });
            }

            Console.ReadLine();
        }
 static SingletonSecClass()
 {
     _singletonSec = new SingletonSecClass();
 }