单列模式

http://www.cnblogs.com/libingql/archive/2012/04/16/2451608.html

/// <summary>    /// 懒汉式    /// </summary>    public class Singleton    {        private static Singleton instance;        private Singleton ()        {        }        private static object synclock = new object();        public static Singleton GetInstance()        {            if (instance == null)            {                lock (synclock)                {                    if (instance == null)                    {                        instance = new Singleton();                    }                }            }            return instance;        }    }    /// <summary>    /// 饿汉式    /// </summary>    public sealed class Singleton2    {        private Singleton2()        {        }        private static readonly Singleton2 instance = new Singleton2();        public static Singleton2 GetInstance()        {            return instance;        }    }