(转)设计模式_Singleton单例模式

　　静态初始化

public sealed class Singleton
{
   private static readonly Singleton instance = new Singleton();
   private Singleton(){}
   public static Singleton Instance
   {
      get
      {
         return instance;
      }
   }
} 

Double-Check Locking  两次检查锁定

public sealed class Singleton
{
   private static volatile Singleton instance;
   private static object syncRoot = new Object();
   private Singleton() {}
   public static Singleton Instance
   {
      get
      {
         if (instance == null)
         {
            lock (syncRoot)
            {
               if (instance == null)
                  instance = new Singleton();
            }
         }
         return instance;
      }
   }
} 
延迟加载

public sealed class Singleton
{
    private static readonly Lazy<Singleton> lazy =
        new Lazy<Singleton>(() => new Singleton());

    public static Singleton Instance { get { return lazy.Value; } }

    private Singleton()
    {
    }
}

延伸阅读：https://msdn.microsoft.com/zh-CN/Library/ms998558.aspx
         http://www.cnblogs.com/rush/archive/2011/10/30/2229565.html