线程的中断(Lock与synchronized)

　　Thread包含interrupt()方法，因此你可以终止被阻塞的任务，这个方法将设置线程的中断状态。如果一个线程已经被阻塞，或者试图执行一个阻塞操作。那么设置这个线程的中断状态将

抛出InterruptedException。当抛出改异常或者该任务调用Thread.interrupted()时，中断状态将被复位。

　　查看Thread的API，关于中断的方法有：

　　void interrupt()   interrupts this thread

　　static boolean interrupted()  Test whether the current thread has been interrupted

　　boolean isInterrupted()  Test whether the current thread has been interrupted

　　通过几个例子看一下中断的用法和特点：

　　例子一，分别模拟了，中断线程sleep，I/O和synchronized修饰的方法。结论：调用interrupt()方法，只有sleep的线程可以被中断，I/O和用synchronized修饰的线程是不能被中断的

public class Interrupting {
    private static ExecutorService service = Executors.newCachedThreadPool();

    static void test(Runnable r) throws InterruptedException{
        Future<?> f = service.submit(r);
        TimeUnit.MILLISECONDS.sleep(100);
        System.out.println("Interrupting: " + r.getClass().getName());
        f.cancel(true); //interrupts if running
        System.out.println("interrupted send to: " + r.getClass().getName());

    }
    public static void main(String[] args) throws Exception{
//        test(new SleepBlocked());
//        test(new IOBlocked(System.in));
        test(new SynchronizedBlocked());
        TimeUnit.SECONDS.sleep(10);
        System.out.println("Aborting with System.exit(0)");
        System.exit(0);
    }
}

class SleepBlocked implements Runnable {
    @Override
    public void run() {
        try {
            TimeUnit.MILLISECONDS.sleep(100);
        } catch (InterruptedException e) {
            System.out.println("InterruptedException");
        }
        System.out.println("Exiting SleepBlocked.run()");
    }
}

class IOBlocked implements Runnable {
    private InputStream is;

    public IOBlocked(InputStream is) {
        this.is = is;
    }

    @Override
    public void run() {
        try {
            System.out.print("waiting for read:");
            is.read();
        } catch (IOException e) {
            if(Thread.currentThread().isInterrupted()) {
                System.out.println("Interrupted IO Blocked");
            } else {
                throw new RuntimeException(e);
            }
        }
        System.out.println("Exiting IOBlocked.run()");
    }
}

class SynchronizedBlocked implements Runnable {
    public SynchronizedBlocked() {
        new Thread(){
            @Override
            public void run() {
                f();
            }
        }.start();
    }

    public synchronized void f() {
        while(true) { //Never release lock
            Thread.yield();
        }
    }
    @Override
    public void run() {
        System.out.println("try to call f()");
        f();
        System.out.println("Exiting SynchronizedBlocked.run()");
    }
}

　　例子二，sleep是可以被中断的，中断后，中断标识位“复位”

package org.burning.sport.javase.thread.interrupt;

import java.util.concurrent.TimeUnit;

public class InterruptSleep implements Runnable{
    @Override
    public void run() {
        try {
            while (true) {
                System.out.println("开始睡了");
                TimeUnit.SECONDS.sleep(3);
            }
        } catch (InterruptedException e) {
            boolean isInterrupt = Thread.interrupted();
            //中断状态被复位
            System.out.println("中断状态:" + isInterrupt);
        }
    }

    public static void main(String[] args) throws Exception{
        Thread t = new Thread(new InterruptSleep());
        t.start();
        TimeUnit.SECONDS.sleep(5);
        t.interrupt();
        System.out.println("interrupted is: " + t.isInterrupted());
    }

}
/*
开始睡了
开始睡了
interrupted is: false
中断状态:false
 */

　　例子三，普通方法是中断不了的，并且从最后的输出结果 interrupted is: true 看出中断标识位没有被清除。

package org.burning.sport.javase.thread.interrupt;

import java.util.concurrent.TimeUnit;

public class InterruptCommonTest implements Runnable{
    @Override
    public void run() {
        while (true) {
            System.out.println("你中断一个试试");
            boolean interrupt = Thread.interrupted();
            System.out.println("中断状态" + interrupt);
        }
    }

    public static void main(String[] args) throws Exception{
        Thread t = new Thread(new InterruptCommonTest());
        t.setDaemon(true);
        t.start();
        TimeUnit.SECONDS.sleep(5);
        t.interrupt();
        System.out.println("interrupted is: " + t.isInterrupted());
    }
}
/*
中断状态false
你中断一个试试
中断状态false
你中断一个试试
中断状态false
interrupted is: true
你中断一个试试
中断状态false
 */

　　总结：你能够中断对sleep的调用（或者任何要求抛出InterruptedException的调用）。但是你不能中断正在试图获取synchronized锁或者正在试图执行IO操作的线程

　　例子四：Lock与中断的关系。

　　 上面的例子中看到，synchronized是不能被中断的，但是Lock是可以被中断的。这个算是synchronized和Lock的不同点。查看Lock的API，有一个方法

　　 void lockInterruptibly() throws InrruptedException 就是可以被中断的方式来获取锁的方法。

package org.burning.sport.javase.thread.interrupt;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

public class InterruptLockTest implements Runnable{
    private static ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {
        try {
            lock.lockInterruptibly();
            while(true) {
                Thread.yield();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

    public static void main(String[] args) throws Exception{
        InterruptLockTest lockTest = new InterruptLockTest();
        Thread t1 = new Thread(lockTest);
        Thread t2 = new Thread(lockTest);
        t1.start();
        t2.start();
        TimeUnit.SECONDS.sleep(3);
        t2.interrupt();
        System.out.println("结束...");
    }
}
/*
结束...
java.lang.InterruptedException
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireInterruptibly(AbstractQueuedSynchronizer.java:898)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(AbstractQueuedSynchronizer.java:1222)
    at java.util.concurrent.locks.ReentrantLock.lockInterruptibly(ReentrantLock.java:335)
    at org.burning.sport.javase.thread.interrupt.InterruptLockTest.run(InterruptLockTest.java:18)
    at java.lang.Thread.run(Thread.java:745)
Exception in thread "Thread-1" java.lang.IllegalMonitorStateException
    at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:151)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1261)
    at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:457)
    at org.burning.sport.javase.thread.interrupt.InterruptLockTest.run(InterruptLockTest.java:25)
    at java.lang.Thread.run(Thread.java:745)
 */

　　

https://gitee.com/play-happy/base-project

参考：

　　【1】《Think in Java》，21.3.4 中断

　　【2】《Java 高并发程序设计》，2.2.3 线程中断