一，介绍
本文记录JAVA多线程中的中断机制的一些知识点。主要是stop方法、interrupted()与isInterrupted()方法的区别，并从源代码的实现上进行简单分析。
JAVA中有3种方式可以终止正在运行的线程
①线程正常退出，即run()方法执行完毕了
②使用Thread类中的stop()方法强行终止线程。但stop()方法已经过期了，不推荐使用
③使用中断机制
线程正常退出没有什么东东，中断机制下面详细介绍，先看下stop()方法的源代码，关键是源代码上的注释。它解释了为什么stop()不安全，stop()方法停止的是哪个线程？
1 /**
2 * Forces the thread to stop executing.
3 * <p>
4 * If there is a security manager installed, its <code>checkAccess</code>
5 * method is called with <code>this</code>
6 * as its argument. This may result in a
7 * <code>SecurityException</code> being raised (in the current thread).
8 * <p>
9 * If this thread is different from the current thread (that is, the current
10 * thread is trying to stop a thread other than itself), the
11 * security manager‘s <code>checkPermission</code> method (with a
12 * <code>RuntimePermission("stopThread")</code> argument) is called in
13 * addition.
14 * Again, this may result in throwing a
15 * <code>SecurityException</code> (in the current thread).
16 * <p>
17 * The thread represented by this thread is forced to stop whatever
18 * it is doing abnormally and to throw a newly created
19 * <code>ThreadDeath</code> object as an exception.
20 * <p>
21 * It is permitted to stop a thread that has not yet been started.
22 * If the thread is eventually started, it immediately terminates.
23 * <p>
24 * An application should not normally try to catch
25 * <code>ThreadDeath</code> unless it must do some extraordinary
26 * cleanup operation (note that the throwing of
27 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
28 * <code>try</code> statements to be executed before the thread
29 * officially dies). If a <code>catch</code> clause catches a
30 * <code>ThreadDeath</code> object, it is important to rethrow the
31 * object so that the thread actually dies.
32 * <p>
33 * The top-level error handler that reacts to otherwise uncaught
34 * exceptions does not print out a message or otherwise notify the
35 * application if the uncaught exception is an instance of
36 * <code>ThreadDeath</code>.
37 *
38 * @exception SecurityException if the current thread cannot
39 * modify this thread.
40 * @see #interrupt()
41 * @see #checkAccess()
42 * @see #run()
43 * @see #start()
44 * @see ThreadDeath
45 * @see ThreadGroup#uncaughtException(Thread,Throwable)
46 * @see SecurityManager#checkAccess(Thread)
47 * @see SecurityManager#checkPermission
48 * @deprecated This method is inherently unsafe. Stopping a thread with
49 * Thread.stop causes it to unlock all of the monitors that it
50 * has locked (as a natural consequence of the unchecked
51 * <code>ThreadDeath</code> exception propagating up the stack). If
52 * any of the objects previously protected by these monitors were in
53 * an inconsistent state, the damaged objects become visible to
54 * other threads, potentially resulting in arbitrary behavior. Many
55 * uses of <code>stop</code> should be replaced by code that simply
56 * modifies some variable to indicate that the target thread should
57 * stop running. The target thread should check this variable
58 * regularly, and return from its run method in an orderly fashion
59 * if the variable indicates that it is to stop running. If the
60 * target thread waits for long periods (on a condition variable,
61 * for example), the <code>interrupt</code> method should be used to
62 * interrupt the wait.
63 * For more information, see
64 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
65 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
66 */
67 @Deprecated
68 public final void stop() {
69 stop(new ThreadDeath());
70 }
上面注释，第9行到第16行表明，stop()方法可以停止“其他线程”。执行thread.stop()方法这条语句的线程称为当前线程，而“其他线程”则是 调用thread.stop()方法的对象thread所代表的线程。
如：
1 public static void main(String[] args) {
2 MyThread thread = new MyThread...
3 //.....
4 thread.stop();
5 //....
6 }
在main方法中，当前线程就是main线程。它执行到第4行，想把“其他线程”thread“ 给停止。这个其他线程就是MyThread类 new 的thread对象所表示的线程。
第21行至23行表明，可以停止一个尚未started(启动)的线程。它的效果是：当该线程启动后，就立马结束了。
第48行以后的注释，则深刻表明了为什么stop()方法被弃用！为什么它是不安全的。
比如说，threadA线程拥有了监视器，这些监视器负责保护某些临界资源，比如说银行的转账的金额。当正在转账过程中，main线程调用 threadA.stop()方法。结果导致监视器被释放，其保护的资源（转账金额）很可能出现不一致性。比如，A账户减少了100，而B账户却没有增加100
二，中断机制
JAVA中如何正确地使用中断机制的细节太多了。interrupted()方法与 isInterrupted()方法都是反应当前线程的是否处于中断状态的。
①interrupted()
1 /**
2 * Tests whether the current thread has been interrupted. The
3 * <i>interrupted status</i> of the thread is cleared by this method. In
4 * other words, if this method were to be called twice in succession, the
5 * second call would return false (unless the current thread were
6 * interrupted again, after the first call had cleared its interrupted
7 * status and before the second call had examined it).
8 *
9 * <p>A thread interruption ignored because a thread was not alive
10 * at the time of the interrupt will be reflected by this method
11 * returning false.
12 *
13 * @return <code>true</code> if the current thread has been interrupted;
14 * <code>false</code> otherwise.
15 * @see #isInterrupted()
16 * @revised 6.0
17 */
18 public static boolean interrupted() {
19 return currentThread().isInterrupted(true);
20 }
从源码的注释中看出，它测试的是当前线程(current thread)的中断状态，且这个方法会清除中断状态。
②isInterrupted()
1 /**
2 * Tests whether this thread has been interrupted. The <i>interrupted
3 * status</i> of the thread is unaffected by this method.
4 *
5 * <p>A thread interruption ignored because a thread was not alive
6 * at the time of the interrupt will be reflected by this method
7 * returning false.
8 *
9 * @return <code>true</code> if this thread has been interrupted;
10 * <code>false</code> otherwise.
11 * @see #interrupted()
12 * @revised 6.0
13 */
14 public boolean isInterrupted() {
15 return isInterrupted(false);
16 }
从源码注释中可以看出，isInterrupted()方法不会清除中断状态。
③interrupted()方法与 isInterrupted()方法的区别
从源代码可以看出，这两个方法都是调用的isInterrupted(boolean ClearInterrupted),只不过一个带的参数是true，另一个带的参数是false。
1 /** 2 * Tests if some Thread has been interrupted. The interrupted state 3 * is reset or not based on the value of ClearInterrupted that is 4 * passed. 5 */ 6 private native boolean isInterrupted(boolean ClearInterrupted);
因此，第一个区别就是，一个会清除中断标识位，另一个不会清除中断标识位。
再分析源码，就可以看出第二个区别在return 语句上：
public static boolean interrupted() {
return currentThread().isInterrupted(true);
}
/************************/
public boolean isInterrupted() {
return isInterrupted(false);
}
interrupted()测试的是当前的线程的中断状态。而isInterrupted()测试的是调用该方法的对象所表示的线程。一个是静态方法（它中断的是当前线程），一个是实例方法（它中断的是实例所表示的线程）。
下面用个具体的例子来更进一步地阐明这个区别。
有一个自定义的线程类如下：
1 public class MyThread extends Thread {
2 @Override
3 public void run() {
4 super.run();
5 for (int i = 0; i < 500000; i++) {
6 System.out.println("i=" + (i + 1));
7 }
8 }
9 }
先看interrupted()方法的示例：
1 public class Run {
2 public static void main(String[] args) {
3 try {
4 MyThread thread = new MyThread();
5 thread.start();
6 Thread.sleep(1000);
7 thread.interrupt();
8 //Thread.currentThread().interrupt();
9 System.out.println("是否停止1？="+thread.interrupted());//false
10 System.out.println("是否停止2？="+thread.interrupted());//false main线程没有被中断!!! //......
第5行启动thread线程，第6行使main线程睡眠1秒钟从而使得thread线程有机会获得CPU执行。
main线程睡眠1s钟后，恢复执行到第7行，请求中断 thread线程。
第9行测试线程是否处于中断状态，这里测试的是哪个线程呢？？？答案是main线程。因为：
（1）interrupted()测试的是当前的线程的中断状态
（2）main线程执行了第9行语句，故main线程是当前线程
再看isInterrupted()方法的示例：
1 public class Run3 {
2 public static void main(String[] args) {
3 try {
4 MyThread thread = new MyThread();
5 thread.start();
6 Thread.sleep(1000);
7 thread.interrupt();
8 System.out.println("是否停止1？="+thread.isInterrupted());//true
在第8行，是thread对象调用的isInterrupted()方法。因此，测试的是thread对象所代表的线程的中断状态。由于在第7行，main线程请求中断 thread线程，故在第8行的结果为: true