Java多线程中断机制三种方法源码分析

Posted 2021-08-06 Vincent-yuan

interrupt()、interrupted()、isInterrupted()

这三个方法都涉及到多线程的一个知识点----中断机制

三个中断方法

中断标识位是JDK源码看不到的，是虚拟机线程实现层面的。

下面结合代码逐一看一下这三个方法的作用，以及为什么中断标识位是虚拟机实现层面的：

1、interrupt()

 1 public void interrupt() {
 2   if (this != Thread.currentThread())
 3     checkAccess();
 4  
 5   synchronized (blockerLock) {
 6     Interruptible b = blocker;
 7     if (b != null) {
 8     interrupt0();    // Just to set the interrupt flag
 9     b.interrupt();
10     return;
11     }
12   }
13   interrupt0();
14   }

结果

1 /* Some private helper methods */
2 private native void setPriority0(int newPriority);
3 private native void stop0(Object o);
4 private native void suspend0();
5 private native void resume0();
6 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

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：

 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 }

1 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：

 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);

 

1 private native boolean isInterrupted(boolean ClearInterrupted);

同样，第2行和第3行的注释已经写得很清楚了，"Theinterruptedstatusofthethreadisclearedbythismethod"，即线程的中断状态由此方法清除。

另外，interrupted()方法和isInterrupted()方法调用的是同一个native方法，无非这个方法传入的是true，表示清除中断标识位

 

参考：

https://www.jb51.net/article/128207.htm