线程Interrupt

Mark

http://blog.csdn.net/hudashi/article/details/6958550

interrupt()只是改变中断状态而已. interrupt()不会中断一个正在运行的线程。这一方法实际上完成的是，给受阻塞的线程抛出一个中断信号，

    这样受阻线程就得以退出阻塞的状态。更确切 的说，如果线程被Object.wait, Thread.join和Thread.sleep三种方法之一阻塞，    那么，它将接收到一个中断异常（InterruptedException），从而提早地终结被阻塞状态。
    如果线程没有被阻塞，这时调用interrupt()将不起作用；否则，线程就将得到InterruptedException异常（该线程必须事先预备好处理此状况），接着逃离阻塞状态。
    线程A在执行sleep,wait,join时,线程B调用线程A的interrupt方法,的确这一个时候A会有InterruptedException 异常抛出来.
    但这其实是在sleep,wait,join这些方法内部会不断检查中断状态的值,而自己抛出的InterruptedException。
    如果线程A正在执行一些指定的操作时如赋值,for,while,if,调用方法等,都不会去检查中断状态
    ,所以线程A不会抛出 InterruptedException,而会一直执行着自己的操作.
    当线程A终于执行到wait(),sleep(),join()时,才马上会抛出 InterruptedException.
    若没有调用sleep(),wait(),join()这些方法,即没有在线程里自己检查中断状态自己抛出InterruptedException的 话,
    那InterruptedException是不会被抛出来的. 
        具体使用见实例1，实例2。
注意1:当线程A执行到wait(),sleep(),join()时,抛出InterruptedException后，中断状态已经被系统复位了，
线程A调用Thread.interrupted()返回的是false

public static boolean interrupted ()

Since: API Level 1

Returns a boolean indicating whether the current Thread ( currentThread()) has a pending interrupt request ( true) or not (false). It also has the side-effect of clearing the flag.

Returns

• a boolean indicating the interrupt status

public boolean isInterrupted ()

Since: API Level 1

Returns a boolean indicating whether the receiver has a pending interrupt request (true) or not ( false)

Returns

• a boolean indicating the interrupt status

1. sleep() & interrupt()
    线程A正在使用sleep()暂停着: Thread.sleep(100000);
    如果要取消他的等待状态,可以在正在执行的线程里(比如这里是B)调用
        a.interrupt();
    令线程A放弃睡眠操作,这里a是线程A对应到的Thread实例
    当在sleep中时 线程被调用interrupt()时,就马上会放弃暂停的状态.并抛出InterruptedException.丢出异常的,是A线程.
2. wait() & interrupt()
    线程A调用了wait()进入了等待状态,也可以用interrupt()取消.
    不过这时候要小心锁定的问题.线程在进入等待区,会把锁定解除,当对等待中的线程调用interrupt()时
    ,会先重新获取锁定,再抛出异常.在获取锁定之前,是无法抛出异常的.
3. join() & interrupt()
    当线程以join()等待其他线程结束时,当它被调用interrupt()，它与sleep()时一样, 会马上跳到catch块里. 
    注意，是对谁调用interrupt()方法,一定是调用被阻塞线程的interrupt方法.如在线程a中调用来线程t.join().
    则a会等t执行完后在执行t.join后的代码,当在线程b中调用来 a.interrupt()方法,则会抛出InterruptedException，当然join()也就被取消了。
实例1：
    static void interruptDemo()
    {
        Thread t1=new Thread(new InterruptDemoRunnable(),"first");
        Thread t2=new Thread(new InterruptDemoRunnable(t1),"second");
        t1.start();
        t2.start();
    }
class InterruptDemoRunnable implements Runnable
{
    long id=0;
    static long count=0;
    Thread t;
    InterruptDemoRunnable()
    {
        this(null);
    }
    InterruptDemoRunnable(Thread t)
    {
        id=count++;
        this.t=t;
    }
    boolean blRun=true;
    public void run()
    {    int cnt=0;
        while(blRun)
        {
            if(t!=null)
            {
                if(cnt==2)
                {
                    t.interrupt();
                    if(t.isInterrupted())
                        System.out.println("set the thread "+t.getName()+" to be Interrupted");
                }
                    
            }
            else
            {    
                try
                {
                    Thread.sleep(1000);
                }
                catch(InterruptedException e)
                {
                    System.out.println("First Interrupted when sleep");
                    System.out.println( "Interrupted is "+Thread.interrupted());//@1
                }
                try
                {
                    Thread.sleep(1);
                }
                catch(InterruptedException e)
                {
                    System.out.println("second Interrupted when sleep");
                }
            }
            System.out.println(id+"run"+cnt);
            cnt++;
            if(cnt==5)
            {
                blRun=false;            
            }
        }
            System.out.println("thread:"+id+"exit");
    }
}
注意1:当线程A执行到wait(),sleep(),join()时,抛出InterruptedException后，中断状态已经被系统复位了。
线程AThread.interrupted()返回的是false
实例2：
    static void interruptDemo()
    {
        Thread t1=new InterruptDemoThread();
        t1.setName("t1");
        Thread t2=new InterruptDemoThread(t1);
        t1.setName("t2");
        t1.start();
        t2.start();
    }
class InterruptDemoThread extends Thread
{
    long id=0;
    static long count=0;
    Thread t;
    InterruptDemoThread()
    {
        this(null);
    }

    InterruptDemoThread(Thread t)
    {
        id=count++;
        this.t=t;
    }
    boolean blRun=true;
    public void run()
    {    int cnt=0;
        while(blRun)
        {
            if(t!=null)
            {
                if(cnt==2)
                {
                    t.interrupt();
                    if(t.isInterrupted())
                        System.out.println("set the thread "+t.getName()+" to be Interrupted");
                }
                    
            }
            else if(isInterrupted())@1
            {    
                /*Thread.interrupted();//@2
                System.out.println("after interrupted(),the state of Interrupted is "+isInterrupted());*/
                try{
                    Thread.sleep(1);
                }
                catch(InterruptedException e)
                {
                    System.out.println("Interrupted when sleep");
                    System.out.println( "Interrupted is "+Thread.interrupted());
                }
            }
            Thread.yield();
            System.out.println(id+"run"+cnt);
            cnt++;
            if(cnt==5)
            {
                blRun=false;            
            }
        }
            System.out.println("thread:"+id+"exit");
    }
}
注意1:如果线程被调用了interrupt()，那么如果此次该线程并不在wait(),sleep(),join()时，
下次执行wait(),sleep(),join()时，一样会抛出InterruptedException，当然抛出后该线程的中断状态也回被系统复位。
注意2:我们可以手动的使用Thread.interrupted()来使当前线程的中断状态系统复位（即清除中断状态）