public class Singleton    {        private static Singleton _instance;        private static readonly object syn = new object();        private Singleton() //构造函数设置private，不能被new，单例模式        {        }        public static Singleton CreateInstance()        {            if (_instance == null)            {                lock (syn)  //加锁防止多线程                {                    if (_instance == null)                    {                        _instance = new Singleton();                    }                }            }            return _instance;        }    }