Java多线程系列 基础篇04 线程中断

1. 中断线程

中断可以理解为线程的一个标志位属性，它表示一个运行中的线程是否被其他线程进行了中断操作，其他线程通过调用该线程的interrupt()方法对其进行中断操作，线程通过检查自身是否被中断来进行响应，线程通过方法isInterrupt()来进行判断是否被中断，也可以调用静态方法Thread.interrupted()对当前线程的中断标志位进行复位，如果该线程已经处于终结状态，即使该线程被中断过，在调用该线程对象的isInterrupted()时依旧会返回false。

2. 终止处于“阻塞状态”的线程和终止处于“运行状态”的线程

/**
 * @Description: 线程中断示例
 * @Author: lizhouwei
 * @CreateDate: 2018/5/20  21:11
 * @Modified By:
 */
public class ThreadInterruptDemo {

    public static void main(String[] args) {
        //sleepThread线程不停的尝试睡眠
        Thread sleepThread = new Thread(new SleepRunner(), "sleepThread");
        sleepThread.setDaemon(true);
        //busyThread不停的运行
        Thread busyThread = new Thread(new BusyRunner(), "busyThread");
        busyThread.setDaemon(true);
        sleepThread.start();
        busyThread.start();
        //主线程睡眠5秒，让sleepThread 和busyThread 充分的运行
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        sleepThread.interrupt();//中断阻塞的线程
        busyThread.interrupt();//中断正在运行的线程

        System.out.println("sleepThread interrupt is " + sleepThread.isInterrupted());
        System.out.println("busyThread interrupt is " + busyThread.isInterrupted());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            System.out.println("1");
            e.printStackTrace();
        }
    }

    static class SleepRunner implements Runnable {
        @Override
        public void run() {
            while (true) {
                try {
                    Thread.sleep(100000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    static class BusyRunner implements Runnable {

        @Override
        public void run() {
            while (true) {
            }
        }
    }
}

从结果可以看出，抛出InterruptException 的是被阻塞的线程SleepThread，其中断标志先被设置为true，随后被复位并抛出异常，而正在运行的线程BusyThread，中断标志位没有没被清除。

安全的终止线程

除了使用中断以外，还可以利用一个boolean变量来控制十五终止该线程。

代码示例：

/**
 * @Description: 使用boolean变量安全的终止线程
 * @Author: lizhouwei
 * @CreateDate: 2018/7/1 20:56
 * @Modified By:
 */
public class ThreadShutdownDemo {

    public static void main(String[] args) {
        Runner oneRunner = new Runner();
        Thread oneThread = new Thread(oneRunner, "oneThread");
        oneThread.start();
        //主线程睡眠1秒，主线程对oneThread 线程进行中断，使oneThread能够感知中断而结束
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        oneThread.interrupt();

        Runner twoRunner = new Runner();
        Thread twoThread = new Thread(twoRunner, "twoThread");
        twoThread.start();
        //主线程睡眠1秒，主线程对twoThread 线程进行中断，使twoThread能够感知中断而结束
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        twoRunner.cancel();
    }

    private static class Runner implements Runnable {

        private long i;
        private volatile boolean running = true;

        @Override
        public void run() {

            while (running && !Thread.currentThread().isInterrupted()) {
                i++;
            }
            System.out.println("count i = " + i);
        }

        public void cancel() {
            running = false;
        }

    }
}

运行结果