怎么中断线程in Java

如何中断线程in Java

http://android.blog.51cto.com/268543/562374

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如何中断Java线程？查看API，不就是用interrupt()方法么？而线程是否已经中断则用Thread.currentThread().isInterrupted()返回true/false：

public class ThreadDemo extends Thread{        public static void main(String[] args) throws InterruptedException {                Thread thread = new ThreadDemo();                thread.start();                thread.sleep(100);                thread.interrupt(); //中断线程        }        @Override        public void run() {                while(!Thread.currentThread().isInterrupted()) {                        System.out.println("thread running");                        try {                                Thread.sleep(100);                        }catch(InterruptedException e)                        {                                System.out.println("InterruptedException");                        }                }                System.out.println("thread interrupted");        }}

?运行结果:
thread running
InterruptedException
thread running
thread running
thread running
thread running
...

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很快发现这方法似乎有问题，线程没有成功中断，于是在处理InterruptedException异常后调用break跳出while循环：

public class ThreadDemo extends Thread{        public static void main(String[] args) throws InterruptedException {                Thread thread = new ThreadDemo();                thread.start();                thread.sleep(100);                thread.interrupt(); //中断线程        }        @Override        public void run() {                while(!Thread.currentThread().isInterrupted()) {                        System.out.println("thread running");                        try {                                Thread.sleep(100);                        }catch(InterruptedException e)                        {                                System.out.println("InterruptedException");                                break;                        }                }                System.out.println("thread interrupted");        }}

运行结果（线程成功中断）:
thread running
InterruptedException
thread interrupted?接着在网上搜索了一下，写了一些例子研究后明白如何写一个可中断的线程。
首先发现在调用线程的start()后，立即调用interrupt()中断线程，线程停止了——被挡在while条件的外面：

public class ThreadDemo extends Thread{        public static void main(String[] args) throws InterruptedException {                Thread thread = new ThreadDemo();                thread.start();                //thread.sleep(100);                thread.interrupt(); //中断线程        }        @Override        public void run() {                System.out.println("in run()");                while(!Thread.currentThread().isInterrupted()) {                        System.out.println("thread running");                        try {                                Thread.sleep(100);                        }catch(InterruptedException e)                        {                                System.out.println("InterruptedException");                                //break;                        }                }                System.out.println("thread interrupted");        }}

?运行结果:
in run()
thread interrupted
然后按照网上说的在异常处理时再次中断，原来这样就能成功地用interrupt方法中断线程：

public class ThreadDemo extends Thread{        public static void main(String[] args) throws InterruptedException {                Thread thread = new ThreadDemo();                thread.start();                thread.sleep(100);                thread.interrupt(); //中断线程        }        @Override        public void run() {                while(!Thread.currentThread().isInterrupted()) {                        System.out.println("thread running");                        try {                                Thread.sleep(100);                        }catch(InterruptedException e)                        {                                System.out.println("InterruptedException");                                Thread.currentThread().interrupt(); //再次中断线程                                //break;                        }                }                System.out.println("thread interrupted");        }}

?运行结果（线程成功中断）:
thread running
InterruptedException
thread interrupted
为什么在调用interrupt()前加上sleep()，导致的结果不同呢？
??我认为Thread对象只有在调用start()时才分配资源创建线程提供给CPU调度。而这过程需要时间，因为时间差，导致了在进入run()方法前，中断标志已经被set on，于是被挡在while条件上。
而再次中断线程，中断标志被set on了，然后循环回到while条件判断，于是退出循环。
而线程被中断后，该对象依然存在的，只是线程不能再次调用start()否则会报异常IllegalThreadStateException。

public class ThreadDemo extends Thread{        public static void main(String[] args){          try{                 ThreadDemo thread = new ThreadDemo();                 thread.start();                 thread.sleep(100);                 thread.interrupt(); //中断线程                 thread.sleep(100);                 thread.printStr();                 thread.interrupt(); //第三次中断线程                 thread.printStr();                 thread.join();          }catch(InterruptedException e){            e.printStackTrace();          }        }        private void printStr(){          System.out.println("thread obj");        }        @Override        public void run() {                while(!Thread.currentThread().isInterrupted()) {                        System.out.println("thread running");                        try {                                Thread.sleep(100);                        }catch(InterruptedException e)                        {                                System.out.println("InterruptedException");                                Thread.currentThread().interrupt(); //再次中断线程                        }                }                System.out.println("thread interrupted");        }}

?运行结果:
thread running
InterruptedException
thread interrupted
thread obj
thread obj?简单总结：
1. 线程start()后马上调用interrupt()，在进入run()时中断标志已经被set on；
2. 在处理sleep()可能抛出的InterruptedException时，再次中断线程即可成功中断；
3. 注意interrupt()方法是set on 中断标志的，interrupted()方法是判断后并清除中断标志的。?isInterrupted()和interrputed()方法的区别
public static boolean interrupted()
??? 测试当前线程是否已经中断。线程的中断状态由该方法清除。换句话说，如果连续两次调用该方法，则第二次调用将返回 false（在第一次调用已清除了其中断状态之后，且第二次调用检验完中断状态前，当前线程再次中断的情况除外）。?public boolean isInterrupted()
??? 测试线程是否已经中断。线程的中断状态不受该方法的影响。?两者都是如果该线程已经中断，则返回 true；否则返回 false。??参考文章 《Java 可中断线程》 http://blog.csdn.net/sapphiron/archive/2008/10/05/3018053.aspx 此文介绍更多的处理其他阻塞情况的中断方法。

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