Java中interrupt的使用

通常我们会有这样的需求,即停止一个线程。在java的api中有stop、suspend等方法可以达到目的,但由于这些方法在使用上存在不安全性,会带来不好的副作用,不建议被使用。具体原因可以参考Why is Thread.stop deprecated

在本文中,将讨论中断在java中的使用。

中断在java中主要有3个方法,interrupt(),isInterrupted()和interrupted()。

  • interrupt(),在一个线程中调用另一个线程的interrupt()方法,即会向那个线程发出信号——线程中断状态已被设置。至于那个线程何去何从,由具体的代码实现决定。
  • isInterrupted(),用来判断当前线程的中断状态(true or false)。
  • interrupted()是个Thread的static方法,用来恢复中断状态,名字起得额🙄。

接下来,看看具体在代码中如何使用。

interrupt()不能中断在运行中的线程,它只能改变中断状态而已。

public class InterruptionInJava implements Runnable{

    public static void main(String[] args) throws InterruptedException {
        Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava");
        //start thread
        testThread.start();
        Thread.sleep(1000);
        //interrupt thread
        testThread.interrupt();

        System.out.println("main end");

    }

    @Override
    public void run() {
        while(true){
            if(Thread.currentThread().isInterrupted()){
                System.out.println("Yes,I am interruted,but I am still running");

            }else{
                System.out.println("not yet interrupted");
            }
        }
    }
}

 结果显示,被中断后,仍旧运行,不停打印Yes,I am interruted,but I am still running

那么,如何正确中断?

既然是只能修改中断状态,那么我们应该针对中断状态做些什么。

public class InterruptionInJava implements Runnable{

    public static void main(String[] args) throws InterruptedException {
        Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava");
        //start thread
        testThread.start();
//        Thread.sleep(1000);
        //interrupt thread
        testThread.interrupt();

        System.out.println("main end");

    }

    @Override
    public void run() {
        while(true){
            if(Thread.currentThread().isInterrupted()){
                System.out.println("Yes,I am interruted,but I am still running");
                return;

            }else{
                System.out.println("not yet interrupted");
            }
        }
    }
}

修改代码,在状态判断中如上,添加一个return就okay了。但现实中,我们可能需要做的更通用,不禁又要发出天问,如何中断线程?答案是添加一个开关

public class InterruptionInJava implements Runnable{
    private volatile static boolean on = false;
    public static void main(String[] args) throws InterruptedException {
        Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava");
        //start thread
        testThread.start();
        Thread.sleep(1000);
        InterruptionInJava.on = true;

        System.out.println("main end");

    }

    @Override
    public void run() {
        while(!on){
            if(Thread.currentThread().isInterrupted()){
                System.out.println("Yes,I am interruted,but I am still running");
            }else{
                System.out.println("not yet interrupted");
            }
        }
    }
}

会输出类似结果,这表明是成功中断了的:

这种开关的方式看起来包治百病,但是当遇到线程阻塞时,就会很无奈了,正如下面代码所示:

public class InterruptionInJava implements Runnable{
    private volatile static boolean on = false;
    public static void main(String[] args) throws InterruptedException {
        Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava");
        //start thread
        testThread.start();
        Thread.sleep(1000);
        InterruptionInJava.on = true;

        System.out.println("main end");

    }

    @Override
    public void run() {
        while(!on){
            try {
                Thread.sleep(10000000);
            } catch (InterruptedException e) {
                System.out.println("caught exception: "+e);
            }
        }
    }
}

线程被阻塞无法被中断。这时候救世主interrupt函数又回来了,它可以迅速中断被阻塞的线程,抛出一个InterruptedException,把线程从阻塞状态中解救出来,show the code。

public class InterruptionInJava implements Runnable{
    private volatile static boolean on = false;
    public static void main(String[] args) throws InterruptedException {
        Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava");
        //start thread
        testThread.start();
        Thread.sleep(1000);
        InterruptionInJava.on = true;
        testThread.interrupt();

        System.out.println("main end");

    }

    @Override
    public void run() {
        while(!on){
            try {
                Thread.sleep(10000000);
            } catch (InterruptedException e) {
                System.out.println("caught exception right now: "+e);
            }
        }
    }
}

结果截图,达到预期。

这种情形同样适用io阻塞,通常io阻塞会立即抛出一个SocketException,类似于上面说的InterruptedException。

 

posted @ 2017-10-07 17:13  无名码者  阅读(45129)  评论(9编辑  收藏  举报