用interrupt()中断Java线程

Java thread 

最近在学习Java线程相关的东西，和大家分享一下，有错误之处欢迎大家指正．

假如我们有一个任务如下，交给一个Java线程来执行，如何才能保证调用interrupt()来中断它呢？

Java代码  

class ATask implements Runnable{

	private double d = 0.0;
	
	public void run() {
		//死循环执行打印"I am running!" 和做消耗时间的浮点计算
		while (true) {
			System.out.println("I am running!");
			
			for (int i = 0; i < 900000; i++) {
				d =  d + (Math.PI + Math.E) / d;
			}
			//给线程调度器可以切换到其它进程的信号
			Thread.yield();
		}
	}
}

public class InterruptTaskTest {
	
	public static void main(String[] args) throws Exception{
		//将任务交给一个线程执行
		Thread t = new Thread(new ATask());
		t.start();
		
		//运行一断时间中断线程
		Thread.sleep(100);
		System.out.println("****************************");
		System.out.println("Interrupted Thread!");
		System.out.println("****************************");
		t.interrupt();
	}
} 

运行这个程序，我们发现调用interrupt()后，程序仍在运行，如果不强制结束，程序将一直运行下去，如下所示:

Java代码  

......
I am running!
I am running!
I am running!
I am running!
****************************
Interrupted Thread!
****************************
I am running!
I am running!
I am running!
I am running!
I am running!
....

虽然中断发生了，但线程仍然在进行，离开线程有两种常用的方法：
抛出InterruptedException和用Thread.interrupted()检查是否发生中断,下面分别看一下这两种方法：
1.在阻塞操作时如Thread.sleep()时被中断会抛出InterruptedException(注意，进行不能中断的IO操作而阻塞和要获得对象的锁调用对象的synchronized方法而阻塞时不会抛出InterruptedException)

Java代码  

class ATask implements Runnable{

	private double d = 0.0;
	
	public void run() {
		//死循环执行打印"I am running!" 和做消耗时间的浮点计算
		try {
			while (true) {
				System.out.println("I am running!");
				
				for (int i = 0; i < 900000; i++) {
					d =  d + (Math.PI + Math.E) / d;
				}
				//休眠一断时间,中断时会抛出InterruptedException
				Thread.sleep(50);
			}
		} catch (InterruptedException e) {
			System.out.println("ATask.run() interrupted!");
		}
	}
}

程序运行结果如下:

Java代码  

I am running!
I am running!
****************************
Interrupted Thread!
****************************
ATask.run() interrupted!

可以看到中断任务时让任务抛出InterruptedException来离开任务．

2.Thread.interrupted()检查是否发生中断.Thread.interrupted()能告诉你线程是否发生中断,并将清除中断状态标记，所以程序不会两次通知你线程发生了中断．

Java代码  

class ATask implements Runnable{

	private double d = 0.0;
	
	public void run() {
		
		//检查程序是否发生中断
		while (!Thread.interrupted()) {
			System.out.println("I am running!");

			for (int i = 0; i < 900000; i++) {
				d = d + (Math.PI + Math.E) / d;
			}
		}

		System.out.println("ATask.run() interrupted!");
	}
}

程序运行结果如下：

Java代码  

I am running!
I am running!
I am running!
I am running!
I am running!
I am running!
I am running!
****************************
Interrupted Thread!
****************************
ATask.run() interrupted!

我们可结合使用两种方法来达到可以通过interrupt()中断线程.请看下面例子:

Java代码  

class ATask implements Runnable{

	private double d = 0.0;
	
	public void run() {
		
		try {
		//检查程序是否发生中断
		while (!Thread.interrupted()) {
			System.out.println("I am running!");
			//point1 before sleep
			Thread.sleep(20);
			//point2 after sleep
			System.out.println("Calculating");
			for (int i = 0; i < 900000; i++) {
				d = d + (Math.PI + Math.E) / d;
			}
		}
		
		} catch (InterruptedException e) {
			System.out.println("Exiting by Exception");
		}
		
		System.out.println("ATask.run() interrupted!");
	}
}

在point1之前处point2之后发生中断会产生两种不同的结果，可以通过修改InterruptTaskTest main()里的Thread.sleep()的时间来达到在point1之前产生中断或在point2之后产生中断.
如果在point1之前发生中断，程序会在调用Thread.sleep()时抛出InterruptedException从而结束线程．这和在Thread.sleep()时被中断是一样的效果.程序运行结果可能如下：

Java代码  

I am running!
Calculating
I am running!
Calculating
I am running!
Calculating
I am running!
****************************
Interrupted Thread!
****************************
Exiting by Exception
ATask.run() interrupted!

如果在point2之后发生中断，线程会继续执行到下一次while判断中断状态时．程序运行结果可能如下：

Java代码  

I am running!
Calculating
I am running!
Calculating
I am running!
Calculating
****************************
Interrupted Thread!
****************************
ATask.run() interrupted!