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:

 

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:

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:

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