【Java并发编程学习】二、线程中断

public class SleepInterrupt extends Object implements Runnable {
    @Override
    public void run() {
        System.out.println("in run() - enter normally");
        try {
            System.out.println("in run() - about to sleep for 20 seconds");
            Thread.sleep(20000);
            System.out.println("in run() - woke up");
        } catch (InterruptedException e) {
            System.out.println("in run() - interrupted while sleeping");
            /**
             * 处理完中断异常后，返回run()方法入口，
             * 若是没有return，线程不会实际被中断，它会继续打印下面的信息
             */
            return;
        }
        System.out.println("in run() - leaving normally");
    }
}

public class InterruptDemo {
    public static void main(String[] args) {
        SleepInterrupt sleepInterrupt = new SleepInterrupt();
        Thread thread = new Thread(sleepInterrupt);
        thread.start();
        // 主线程休眠2秒，从而确保刚才启动的线程有机会执行一段时间
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("in main() - interrupting other thread");
        /**
         * 当一个线程运行时，另外一个线程能够调用对应的Thread对象的interrupt()方法来中断它，
         * 该方法只是在目标线程中设置一个标志，表示它已经被中断，并当即返回
         */
        thread.interrupt();
        System.out.println("in main() - leaving");
    }
}

public class PendingInterrupt extends Object {
    public static void main(String[] args) {
        /**
         *  若是输入了参数，则在main线程中中断当前线程（亦即main线程），除了将中断标志设置为true外，线程被中断了，可是main线程
         *  仍然运行，main线程继续监视实时时钟，并进入try块，一旦调用sleep()方法，它就会注意到待决中断的存在，并抛出
         *  InterruptException.
         */
        if (args.length > 0) {
            Thread.currentThread().interrupt();
        }
        // 获取当前时间
        long startTime = System.currentTimeMillis();
        /**
         *  若是线程在调用sleep()方法前被中断，那么该中断称为待决中断，它会在刚调用sleep()方法时，
         *  当即抛出InterruptedException异常
         */
        try {
            Thread.sleep(2000);
            System.out.println("[PendingInterrupt] was NOT interrupted");
        } catch (InterruptedException e) {
            System.out.println("[PendingInterrupt] was interrupted");
        }
        // 计算中间代码执行的时间
        System.out.println("[PendingInterrupt] elapsedTime=" + (System.currentTimeMillis() -  startTime));
    }
}

/**
 * 使用Thread对象上调用isInterrupted()方法来检查任何线程的中断状态
 * 线程一旦被中断，isInterrupted()方法便会返回true，而一旦sleep（）方法抛出异常，它将清空中断标志，
 * 此时isInterrupted()方法将返回false
 */
public class InterruptCheck extends Object {
    public static void main(String[] args) {
        Thread thread = Thread.currentThread();
        System.out.println("[InterruptCheck] Point A: thread.isInterrupted()= " + thread.isInterrupted());
        thread.interrupt();
        System.out.println("[InterruptCheck] Point B: thread.isInterrupted()= " + thread.isInterrupted());

        try {
            Thread.sleep(2000);
            System.out.println("[InterruptCheck] was NOT interrupted");
        } catch (InterruptedException e) {
            System.out.println("[InterruptCheck] was interrupted");
        }
        System.out.println("[InterruptCheck] Point C: thread.isInterrupted()= " + thread.isInterrupted());
    }
}

/**
 * 使用Thread.interrupted()方法判断中断状态（并隐式重置为false）
 * 因为它是静态方法、所以不能在特定的线程上使用，而只能报告调用它的线程的中断状态，若是线程被中断，
 * 并且中断状态尚不清楚，那么，这个方法返回true。与isInterrupted不一样，它将自动重置中断状态为false.
 * 
 */
public class InterruptReset extends Object {
    public static void main(String[] args) {
        System.out.println("[InterruptReset] Point X: Thread.interrupted()= " + Thread.interrupted());
        Thread.currentThread().interrupt();
        System.out.println("[InterruptReset] Point Y: Thread.interrupted()= " + Thread.interrupted());
        System.out.println("[InterruptReset] Point Z: Thread.interrupted()= " + Thread.interrupted());
    }
}