设计模式之单例模式(线程安全)

 1 public class Singleton
 2 {
 3     private static Singleton _instance = null;
 4     private Singleton(){}
 5     public static Singleton CreateInstance()
 6     {
 7         if(_instance == null)
 8 
 9         {
10             _instance = new Singleton();
11         }
12         return _instance;
13     }
14 }

 1 public class Singleton
 2 {
 3     private volatile static Singleton _instance = null;
 4     private static readonly object lockHelper = new object();
 5     private Singleton(){}
 6     public static Singleton CreateInstance()
 7     {
 8         if(_instance == null)
 9         {
10             lock(lockHelper)
11             {
12                 if(_instance == null)
13                      _instance = new Singleton();
14             }
15         }
16         return _instance;
17     }
18 }

1 public class Singleton
2 {
3 
4     private Singleton(){}
5     public static readonly Singleton instance = new Singleton();
6 }  

 1 public class Singleton
 2 {
 3     private volatile static Singleton _instance = null;
 4     private static readonly object lockHelper = new object();
 5     private Singleton(){}
 6     public static Singleton CreateInstance()
 7     {
 8         if(_instance == null)
 9         {
10 
11 bool lockTaken = false;
12 try
13 {
14 　　System.Threading.Monitor.Enter(lockHelper , ref lockTaken);
15 　　if (_instance == null)
16 　　{
17 　　　　_instance = new Singleton();
18 　　}
19 }
20 finally
21 {
22 　　if (lockTaken)
23 　　{
24 　　　　System.Threading.Monitor.Exit(lockHelper);
25 　　}
26 }
27 
28         }
29 
30         return _instance;
31 
32     }
33 
34 }