单例模式

 1     //1、线程不安全
 2     //public sealed class Singleton
 3     //{
 4     //    private static Singleton instance; //定义私有的静态全局变量保存改类的唯一实例
 5     //    private Singleton() { }
 6     //    public static Singleton GetInstance()
 7     //    {
 8     //        //如果该类没有被实例化，才去创建改实例
 9     //        return instance ?? (instance=new Singleton());
10     //    }
11     //}
12 
13 
14     //2、线程安全
15     //public sealed class Singleton
16     //{
17     //    private static Singleton instance = null;
18     //    //创建静态只读的进程辅助对象
19     //    private static readonly object _lock = new object();
20     //    Singleton() { }
21     //    public static Singleton GetInstance()
22     //    {
23     //        lock (_lock)
24     //        {
25     //            return instance ?? (instance = new Singleton());
26     //        }
27     //    }
28     //}
29 
30 
31 
32     //3、线程安全 双重锁定
33     //public sealed class Singleton
34     //{
35     //    private static Singleton instance;
36     //    private static object _lock = new object();
37     //    private Singleton() { }
38     //    public static Singleton GetInstance()
39     //    {
40     //        if (instance == null)//实例为空时，才加锁创建
41     //        {
42     //            lock (_lock)//保证只有一个线程可以访问改语句块
43     //            {
44     //                    instance = instance ?? (new Singleton());
45     //            }
46     //        }
47     //        return instance;
48     //    }
49     //}
50 
51 
52 
53 
54     //4、线程安全 静态初始化
55     //public sealed class Singleton
56     //{
57     //    private static Singleton instance = new Singleton();
58     //    private Singleton() { }
59     //    public static Singleton GetInstance()
60     //    {
61     //        return instance;
62     //    }
63     //}
64 
65 
66     //5、延迟初始化，内部类
67     //public sealed class Singleton
68     //{
69     //    private Singleton() { }
70     //    public static Singleton GetInstance()
71     //    {
72     //        return Nested.instance;
73     //    }
74     //    //初始化工作放到Nested类中的静态成员来完成
75     //    private class Nested
76     //    {
77     //        static Nested() { }
78     //        internal static readonly Singleton instance = new Singleton();
79     //    }
80     //}
81 
82 
83     //6、延迟初始化，线程安全
84     public sealed class Singleton
85     {
86         private static readonly Lazy<Singleton> lazy = new Lazy<Singleton>(() => new Singleton());
87         public static Singleton GetInstance()
88         {
89             return lazy.Value;
90         }
91         private Singleton() { }   
92     }