Java多线程中断机制
thread中的三个方法：interrupt()、interrupted()、isInterrupted()
1、interrupt()
public void interrupt() {
if (this != Thread.currentThread())
checkAccess();
synchronized (blockerLock) {
Interruptible b = blocker;
if (b != null) {
interrupt0(); // Just to set the interrupt flag
b.interrupt();
return;
}
}
interrupt0();
}
/* Some private helper methods */
private native void setPriority0(int newPriority);
private native void stop0(Object o);
private native void suspend0();
private native void resume0();
private native void interrupt0();
分两部分看：
（1）第一部分的第8行注释说得很清楚了，interrupt0()方法的作用是"Just to set the interrupt flag"，即方法的作用仅仅是设置中断标识位
（2）第二部分的第6行就是interrupt0()方法的原型，由于方法是被native修饰的，很明显这是一个本地方法，是Java虚拟机实现的。
当对一个线程，调用 interrupt() 时，
-
如果线程处于被阻塞状态（例如处于sleep, wait, join 等状态），那么线程将立即退出被阻塞状态，并抛出一个InterruptedException异常。
-
如果线程处于正常活动状态，那么会将该线程的中断标志设置为 true。被设置中断标志的线程将继续正常运行，不受影响。
2、isInterrupted()
方法唯一的作用只是测试线程是否已经中断，中断标识位的状态并不受到该方法的影响，看一下Java是如何实现这个方法的：
/**
* Tests whether this thread has been interrupted. The <i>interrupted
* status</i> of the thread is unaffected by this method.
*
* <p>A thread interruption ignored because a thread was not alive
* at the time of the interrupt will be reflected by this method
* returning false.
*
* @return <code>true</code> if this thread has been interrupted;
* <code>false</code> otherwise.
* @see #interrupted()
* @revised 6.0
*/
public boolean isInterrupted() {
return isInterrupted(false);
}
private native boolean isInterrupted(boolean ClearInterrupted);
注意一下第一部分的第2行和第3行，"The interrupted statis of the thread is unaffected by this method"，即线程的中断状态不受到这个方法的影响。最终调用的是isInterrupted(boolean ClearInterrupted)，这个方法是一个native的，看得出也是Java虚拟机实现的。方法的参数ClearInterrupted，顾名思义，清除中断标识位，这里传递false，明显就是不清除。
3、interrupted()
方法的作用是测试当前线程是否已经中断，线程的中断标识位由该方法清除。换句话说，连续两次调用该方法的返回值必定是false。看一下这个方法是如何实现的：
/**
* Tests whether the current thread has been interrupted. The
* <i>interrupted status</i> of the thread is cleared by this method. In
* other words, if this method were to be called twice in succession, the
* second call would return false (unless the current thread were
* interrupted again, after the first call had cleared its interrupted
* status and before the second call had examined it).
*
* <p>A thread interruption ignored because a thread was not alive
* at the time of the interrupt will be reflected by this method
* returning false.
*
* @return <code>true</code> if the current thread has been interrupted;
* <code>false</code> otherwise.
* @see #isInterrupted()
* @revised 6.0
*/
public static boolean interrupted() {
return currentThread().isInterrupted(true);
private native boolean isInterrupted(boolean ClearInterrupted);
而如果一个线程被设置中断标识后，进行了一些处理后选择继续进行任务， 而且这个任务也是需要被中断的，那么当然需要清除标志位了。
example
org.springframework.scheduling.concurrent.ExecutorConfigurationSupport
注意代码中Thread.currentThread().interrupt();的用法。
/**
* Perform a shutdown on the underlying ExecutorService.
* @see java.util.concurrent.ExecutorService#shutdown()
* @see java.util.concurrent.ExecutorService#shutdownNow()
* @see #awaitTerminationIfNecessary()
*/
public void shutdown() {
if (logger.isInfoEnabled()) {
logger.info("Shutting down ExecutorService" + (this.beanName != null ? " '" + this.beanName + "'" : ""));
}
if (this.waitForTasksToCompleteOnShutdown) {
this.executor.shutdown();
}
else {
this.executor.shutdownNow();
}
awaitTerminationIfNecessary();
}
/**
* Wait for the executor to terminate, according to the value of the
* {@link #setAwaitTerminationSeconds "awaitTerminationSeconds"} property.
*/
private void awaitTerminationIfNecessary() {
if (this.awaitTerminationSeconds > 0) {
try {
if (!this.executor.awaitTermination(this.awaitTerminationSeconds, TimeUnit.SECONDS)) {
if (logger.isWarnEnabled()) {
logger.warn("Timed out while waiting for executor" +
(this.beanName != null ? " '" + this.beanName + "'" : "") + " to terminate");
}
}
}
catch (InterruptedException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Interrupted while waiting for executor" +
(this.beanName != null ? " '" + this.beanName + "'" : "") + " to terminate");
}
Thread.currentThread().interrupt();
}
}
}
