ThreadPoolExecutor(四)——Interrupt

1.补充知识

说ThreadPoolExecutor之前先要说先补充知识，关于Thread的interrupt相关操作。

还有一篇博客比较言简意赅，interrupt、interrupted 、isInterrupted 区别

interrupt对于处于sleep，wait状态的线程会进行interrupt并抛出InterruptedException，同时擦除中断标志位，也就是说，这时候如果再用isInterrupted或者静态interrupted方法获取中断标志位的时候，得到的是false。

interrupt对于正常运行的线程起不到中断作用，只是把该线程的中断标志位设置为true了，线程会继续正常运行。

Thread静态interrupted方法判断标志位的时候也会清除标志位。也就是说一个线程被中断了，在线程中用interrupted判断时返回true，再次调用该方法判断会返回false。

Thread的成员函数isInterrupted判断标志位的时候不会清除标志位，如果返回true，那么无论执行多少次都会返回true(期间没有其他清除标志位的操作的话)。

2.处于sleep状态下的打断

public static void test1() throws Exception {        final Thread thread = new Thread(new Runnable() {            @Override public void run() {                try {                    Thread.sleep(2000);                } catch (InterruptedException e) {                    e.printStackTrace();                    System.out.println("thread is interrupted!!!!!!!!!!2");                    System.out.println("isInterrupted:" + Thread.interrupted());                }            }        });        thread.start();        new Thread(new Runnable() {            @Override public void run() {                // 会打断上面那个线程的sleep                thread.interrupt();            }        }).start();        System.out.println("over");        System.in.read();    }

运行结果如下：

java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at com.qunar.flight.brandnew.java.thread.TInterrupt$1.run(TInterrupt.java:23)
at java.lang.Thread.run(Thread.java:722)
over
thread is interrupted!!!!!!!!!!2

说明处于sleep状态的thread线程被中断并抛出了异常。这里Thread.interrupted()方法返回是false，因为抛出异常之后就清除了中断标志位了。

3.处于wait状态下的中断

private static Object lock = new Object();    public static void test2() throws Exception {        final Thread thread = new Thread(new Runnable() {            @Override public void run() {                try {                    synchronized (lock) {                        lock.wait();                    }                } catch (InterruptedException e) {                    e.printStackTrace();                    System.out.println("thread is interrupted!!!!!!!!!!1");                }            }        });        thread.start();        new Thread(new Runnable() {            @Override public void run() {                System.out.println("interrupt");                thread.interrupt();            }        }).start();        System.out.println("over");        System.in.read();    }

结果：

over
interrupt
thread is interrupted!!!!!!!!!!
isInterrupted:false
java.lang.InterruptedException

这里和上面wait的情况基本一致。

4.线程正常运行时的interrupt

public static void test5() throws Exception {        final Thread thread = new Thread(new Runnable() {            @Override public void run() {                for (int i = 0; i < 1000; i++) {                    for (int j = 0; j < 100000; j++) {                        System.currentTimeMillis();                    }                }                System.out.println("isInterrupted:" + Thread.interrupted());                System.out.println("isInterrupted:" + Thread.currentThread().isInterrupted());            }        });        thread.start();        Thread thread2 = new Thread(new Runnable() {            @Override public void run() {                thread.interrupt();            }        });        thread2.start();        System.out.println("over");        System.in.read();    }

结果：

over
isInterrupted:true
isInterrupted:false

这里中断的时候thread线程依然正常运行，只是中断标志位被置位true了。Thread.interrupted()方法判断的时候返回了true，同时擦除了中断标志位，所以再用Thread.currentThread().isInterrupted()判断的时候，就返回false了。

5.处于park状态下的interrupt

public static void test6() throws Exception {        final Thread thread = new Thread(new Runnable() {            @Override public void run() {                LockSupport.park();                System.out.println("isInterrupted:" + Thread.interrupted());                System.out.println("isInterrupted:" + Thread.currentThread().isInterrupted());            }        });        thread.start();        Thread thread2 = new Thread(new Runnable() {            @Override public void run() {                thread.interrupt();            }        });        thread2.start();        System.out.println("over");        System.in.read();    }

结果：

over
isInterrupted:true
isInterrupted:false

和线程正常运行下的返回结果相同。

说明interrupt可以中断处于park状态的线程，但是不会抛出InterruptedException异常，只是设置中断标志位。

AbstractQueuedSynchronizer的doAcquireInterruptibly方法就是根据parkAndCheckInterrupt的返回值，在park状态被唤醒的时候，判断线程是被中断的还是被unpark唤醒的，决定后续的操作是抛出异常还是继续去获得锁。