C# lock的应用

最近遇到一个问题，就是多个线程以相同的邮箱账号访问邮件服务器的时候登录会报错，说明多个线程不能在同一时刻用同一账号进行登录，但是不同账号之间又互不影响，因此针对每一个不同的账号需要对其加一把锁，既可以防止报错又可以不影响其他账号登陆。方法就是新建一个dictionary，来装 object，代码如下：

 1 public static bool operator !=(MailSyncFolder a, MailSyncFolder b)
 2         {
 3             return !(a == b);
 4         }
 5 
 6         static Dictionary<string, object> dics = new Dictionary<string, object>();
 7         public static object GetLock(string userName)
 8         {
 9             lock (dics)
10             {
11                 if (dics.ContainsKey(userName))
12                 {
13                     return dics[userName];
14                 }
15                 else
16                 {
17                     object obj = new object();
18                     dics.Add(userName, obj);
19                     return obj;
20                 }
21             }
22         }
23 
24 
25 
26 
27         /// <summary>
28         /// 连接到邮箱服务器
29         /// </summary>
30         /// <returns></returns>
31         private Pop3Client ConnectToMailServer(string userName)
32         {
33             object lockObj = GetLock(userName);
34             lock (lockObj)
35             {
36                 Pop3Client pop3Client = null;
37                 try
38                 {
39                     pop3Client = new Pop3Client();
40                     pop3Client.Connect(HostIP, Port, false);
41                     //pop3Client.Connect(HostIP, 110, false);
42                     pop3Client.Authenticate(UserName, Password);//相同的username用锁来实现共享，不同的username不需要锁，怎么实现？
43                 }
44                 catch (InvalidLoginException e)
45                 {
46                     if (pop3Client.Connected)
47                     {
48                         pop3Client.Disconnect();
49                     }
50                     log.Warn("The server did not accept the user credentials! POP3 Server Authentication");
51                     throw e;
52                 }
53                 catch (PopServerNotFoundException e)
54                 {
55                     if (pop3Client.Connected)
56                     {
57                         pop3Client.Disconnect();
58                     }
59                     log.Warn("The server could not be found! POP3 Retrieval");
60                     throw e;
61                 }
62                 catch (PopServerLockedException e)
63                 {
64                     if (pop3Client.Connected)
65                     {
66                         pop3Client.Disconnect();
67                     }
68                     log.Warn("The mailbox is locked. It might be in use or under maintenance. Are you connected elsewhere? POP3 Account Locked");
69                     throw e;
70                 }
71                 catch (LoginDelayException e)
72                 {
73                     if (pop3Client.Connected)
74                     {
75                         pop3Client.Disconnect();
76                     }
77                     log.Warn("Login not allowed. Server enforces delay between logins. Have you connected recently? POP3 Account Login Delay");
78                     throw e;
79                 }
80                 catch (Exception e)
81                 {
82                     if (pop3Client.Connected)
83                     {
84                         pop3Client.Disconnect();
85                     }
86                     log.Warn("Error occurred retrieving mail. " + e.Message + " POP3 Retrieval");
87                     throw e;
88                 }
89 
90                 return pop3Client;
91             }
92         }