interrupt
下面是interrupt方法的文档的一部分：
* <p> If this thread is blocked in an invocation of the {@link
* Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
* Object#wait(long, int) wait(long, int)} methods of the {@link Object}
* class, or of the {@link #join()}, {@link #join(long)}, {@link
* #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
* methods of this class, then its interrupt status will be cleared and it
* will receive an {@link InterruptedException}.
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如果线程由于调用Object类的wait()方法、Thread类的join()实例方法以及Thread.sleep()静态方法而被挂起，此时其他线程调用了这个线程的interrupt方法，那么这个线程的中断状态会被清除，并会抛出一个InterruptedException异常。
从上面加粗的文字中可以得出两点结论：
1 即便调用了interrupt方法，之后用isInterrupted()方法检查它的中断状态时也不一定能得到true。
2 如果线程当前运行处的代码块不对InterruptedException异常进行合适的处理，那么interrupt方法就没有任何效果。
举一个例子来验证上面的结论：
public abstract class StoppableThread extends Thread {
@Override
public void run() {
while(!isInterrupted()){
System.out.println("isInterrupted: " + isInterrupted());
doWork();
}
System.out.println("END");
}
protected abstract void doWork();
public static void main(String[] args) {
StoppableThread thread = new StoppableThread() {
@Override
protected void doWork() {
System.out.println("running...");
try {
sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
thread.start();
try {
Thread.sleep(2200);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("即将调用interrupt()方法");
thread.interrupt();
}
}
输出结果：
isInterrupted: false
running...
isInterrupted: false
running...
isInterrupted: false
running...
isInterrupted: false
running...
isInterrupted: false
running...
即将调用interrupt()方法
isInterrupted: false
running...
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at readerandwriter.StoppableThread$1.doWork(StoppableThread.java:22)
at readerandwriter.StoppableThread.run(StoppableThread.java:9)
isInterrupted: false
running...
isInterrupted: false
running...
InterruptedException
interrupt方法所做的仅仅是设置了Thread对象的中断状态，InterruptedException是在线程的wait()、sleep()、join()等方法中抛出的。
修改上面的那个类的doWork()方法，让它声明抛出InterruptedException，并把实现中的sleep(500)去掉。
public abstract class StoppableThread extends Thread {
@Override
public void run() {
while(!isInterrupted()){
System.out.println("isInterrupted: " + isInterrupted());
try {
doWork();
} catch (InterruptedException e) {
System.out.println("InterruptedException is Thrown");
}
}
System.out.println("END");
}
protected abstract void doWork() throws InterruptedException;
public static void main(String[] args) {
StoppableThread thread = new StoppableThread() {
@Override
protected void doWork() throws InterruptedException{
System.out.println("running...");
}
};
thread.start();
try {
Thread.sleep(2200);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("即将调用interrupt()方法");
thread.interrupt();
}
}
输出结果：
isInterrupted: false
running...
isInterrupted: false
running...
isInterrupted: false
running...
isInterrupted: false
running...
isInterrupted: false
running...
即将调用interrupt()方法
isInterrupted: false
running...
END
虽然线程结束了，但是InterruptedException异常并没有被抛出（如果抛出了会输出一行InterruptedException is Thrown）。线程是因为isInterrupted()返回true才退出循环的。结合上面interrupt方法的文档，可以得出两条结论：
1 interrupt仅仅设置了Thread对象的中断状态，InterruptedException是在线程的wait()、sleep()、join()等方法中抛出的，并且抛出后会清除掉Thread对象的中断状态。
2 当线程正在执行一些常规方法时，即便调用了interrupt方法也不会抛出InterruptedException，但会导致isInterrupted()方法返回true。
Thread.interrupted
Thread类的静态方法interrupted()用来检查当前线程的中断状态。这个方法除了返回当前线程的中断状态（true/false），还会把中断状态给清除掉。也就是说，如果连续调用两次这个方法，那么第二次必然返回的是false，因为无论中断状态原本是什么，它都已经被第一次的Thread.interrupted()清除了。
如何安全可靠地中断线程
没有一个完美的方法能够实现在调用某个方法的瞬间就让线程退出。
一个比较好的方法是在Thread子类中添加一个标志位，这里命名为isShutdownRequested，默认为false，并提供一个用于在interrupt的同时设置它为true的方法。最后，在线程的run()方法的while循环控制条件中利用这个标志位判断线程是否被要求中止。
下面提供一个StoppableThread实现，里面包含一个shutdown()方法，用于中止线程：
public abstract class StoppableThread extends Thread {
private volatile boolean isShutdownRequested = false;
public final void shutdown(){
isShutdownRequested = true;
interrupt();
}
public final boolean isShutdownRequested() {
return isShutdownRequested;
}
@Override
public void run() {
try {
while(!isShutdownRequested()){
doWork();
}
} catch (InterruptedException e) {
System.out.println("InterruptedException is Thrown");
} finally {
doShutdown();
}
}
protected abstract void doWork() throws InterruptedException;
protected abstract void doShutdown();
public static void main(String[] args) {
StoppableThread thread = new StoppableThread() {
@Override
protected void doWork() throws InterruptedException {
System.out.println("running...");
sleep(500);
}
@Override
protected void doShutdown() {
System.out.println("shutdown!");
}
};
thread.start();
try {
Thread.sleep(2200);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("即将调用shutdown()方法");
thread.shutdown();
}
}
输出结果：
running...
running...
running...
running...
running...
即将调用shutdown()方法
InterruptedException is Thrown
shutdown!
参考资料