Design Patterns 乌蒙山连着山外山---单件模式singleton pattern

 1     //包含单件实例的类Singleton
 2     public class Singleton
 3     {
 4         //声明用于存储单件实例的变量instance
 5         private static Singleton instance;
 6         //定义用于标识同步线程的对象locker
 7         private static Object locker = new Object();
 8         //私有的构造函数Singleton
 9         private Singleton() { }
10         //公共访问的返回单件实例的函数GetInstance
11         public static Singleton GetInstance()
12         {
13             //第一重“锁”只为了提高些性能
14             if (instance == null)
15             {
16                 //线程锁定块
17                 lock (locker)
18                 {
19                     //第二重“锁”防止多线程多次new实例
20                     if (instance == null)
21                     {
22                         //new唯一实例
23                         instance = new Singleton();
24                     }
25                 }
26             }
27             //返回单件实例
28             return instance;
29         }
30     }