Lock语句（C# ）

最新推荐文章于 2023-10-31 18:23:52 发布

转载最新推荐文章于 2023-10-31 18:23:52 发布 · 143 阅读

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原文链接：http://www.cnblogs.com/wxin/p/3469878.html

Lock关键字用于将指定对象进行锁定，防止其他线程对此对象进行访问操作，直到代码块内的语句执行完毕，然后释放该锁。

1 Object thisLock = new Object();
2 lock (thisLock)
3 {
4     // Critical code section.
5 }

如以下多线程对同一对象进行操作的代码中lock语句被注释了，那么运行结果将会显示各线程之间进行了交叉操作，所以也非常容易抛出异常。但是添加了lock语句将会使代码执行时间增长，因为多了线程间的等待，所以还是要根据需要来进行使用。

 1 using System;
 2 using System.Threading;
 3 
 4 class Account
 5 {
 6     private Object thisLock = new Object();
 7     int balance;
 8 
 9     Random r = new Random();
10 
11     public Account(int initial)
12     {
13         balance = initial;
14     }
15 
16     int Withdraw(int amount)
17     {
18 
19         // This condition will never be true unless the lock statement
20         // is commented out:
21         if (balance < 0)
22         {
23             throw new Exception("Negative Balance");
24         }
25 
26         // Comment out the next line to see the effect of leaving out 
27         // the lock keyword:
28         lock (thisLock)
29         {
30             if (balance >= amount)
31             {
32                 Console.WriteLine("Balance before Withdrawal :  " + balance);
33                 Console.WriteLine("Amount to Withdraw        : -" + amount);
34                 balance = balance - amount;
35                 Console.WriteLine("Balance after Withdrawal  :  " + balance);
36                 return amount;
37             }
38             else
39             {
40                 return 0; // transaction rejected
41             }
42         }
43     }
44 
45     public void DoTransactions()
46     {
47         for (int i = 0; i < 100; i++)
48         {
49             Withdraw(r.Next(1, 100));
50         }
51     }
52 }
53 
54 class LockCode
55 {
56     static void Main()
57     {
58         Thread[] threads = new Thread[10];
59         Account acc = new Account(1000);
60         for (int i = 0; i < 10; i++)
61         {
62             Thread t = new Thread(new ThreadStart(acc.DoTransactions));
63             threads[i] = t;
64         }
65         for (int i = 0; i < 10; i++)
66         {
67             threads[i].Start();
68         }
69     }
70 }

View Code

如果将上面代码改为对多个对象进行操作，不管加不加lock语句，自然对结果都不产生影响的。

 1     static void Main()
 2     {
 3         Thread[] threads = new Thread[10];
 4         Account[] accArr = new Account[10];
 5 
 6         for (int i = 0; i < 10; i++)
 7         {
 8             accArr[i] = new Account(1000);
 9             Thread t = new Thread(accArr[i].DoTransactions);
10             t.Start("Thread " + i);
11         }
12     }