C#中lock关键字

lock关键字可以用来确保代码块完成运行，而不会被其他线程中断。这是通过在代码块运行期间为给定对象获取互斥锁来实现的。

首先定义Account类,如下所示:

 

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public class Account {     private int balance = 500;       public void WithDraw(int amount)     {                           if (balance - amount > 0)             {                 Console.WriteLine("{1}:before drawing:balance:{0},amount:{2}", balance, Thread.CurrentThread.Name, amount);                 Thread.Sleep(500);                 balance -= amount;                 Console.WriteLine("{1}:after drawing:balance:{0},amount:{2}", balance, Thread.CurrentThread.Name, amount);                 Console.WriteLine();               }             else             {                 Console.WriteLine("{0}:no money", Thread.CurrentThread.Name);                 Thread.CurrentThread.Abort();             }                   }       public void DoTrans()     {         Random ran = new Random();           for (int i = 0; i < 10; i++)         {             WithDraw(ran.Next(50, 100));                           }     } }

该类中定义了某个帐户初使金额是500元,WithDraw方法用于从帐户中取钱,并在取钱之前判断要取的金额是否大于余额,在判断后如果满足条件则执行减操作,此处使用Thread.Sleep方法模拟操作过程中一些耗时操作以允许其他线程有机会执行.

 

DoTrans方法用于分10次随机从帐户中取款.接下来定义Main方法使用两个线程取款:

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static void Main(string[] args) {                 Account a1 = new Account();       Thread t1 = new Thread(new ThreadStart(a1.DoTrans));     Thread t2 = new Thread(new ThreadStart(a1.DoTrans));       t1.Name = "Thread 11111";     t2.Name = "Thread 22222";       t1.Start();     t2.Start();       Console.ReadLine(); }

运行项目会发现由于两个线程同时取款,在其中一个线程判断满足条件后休眠,由另外一个线程取款,取完款后再返回来执行第一个线程的取款操作,此时一线程已经执行过判断,继承取款会导致负数余额的产生.

因此解决方法可以使用lock关键字,将Account的WithDraw方法修正如下:

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public void WithDraw(int amount) {     lock (this)     {         if (balance - amount > 0)         {             Console.WriteLine("{1}:before drawing:balance:{0},amount:{2}", balance, Thread.CurrentThread.Name, amount);             Thread.Sleep(500);             balance -= amount;             Console.WriteLine("{1}:after drawing:balance:{0},amount:{2}", balance, Thread.CurrentThread.Name, amount);             Console.WriteLine();           }         else         {             Console.WriteLine("{0}:no money", Thread.CurrentThread.Name);             Thread.CurrentThread.Abort();         }     } }

可以保证该代码块不能被中断,从而使帐户金额不会产生负数的情况