Java多线程（十二）：中断机制

这里详细分析interrupt(),interrupted(),isInterrupted()三个方法

interrupt()

中断这个线程，设置中断标识位

    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(this);
                return;
            }
        }
        interrupt0();
    }

我们来找下如何设置中断标识位的

找到interrupt0()的源码，src/hotspot/share/prims/jvm.cpp

JVM_ENTRY(void, JVM_Interrupt(JNIEnv* env, jobject jthread))
  ...
  if (is_alive) {
    // jthread refers to a live JavaThread.
    Thread::interrupt(receiver);
  }
JVM_END

调用了Thread::interrupt方法

src/hotspot/share/runtime/thread.cpp

void Thread::interrupt(Thread* thread) {
  ...
  os::interrupt(thread);
}

os::interrupt方法，src/hotspot/os/posix/os_posix.cpp

void os::interrupt(Thread* thread) {
  ...
  OSThread* osthread = thread->osthread();
  if (!osthread->interrupted()) {
    //设置中断标识位
    osthread->set_interrupted(true);
    ...
  }
    ...
}

isInterrupted()

测试线程是否被中断，线程的中断状态不会改变

public boolean isInterrupted() {
        return isInterrupted(false);
    }

查看native isInterrupted(boolean ClearInterrupted)源码，查找方式同上

src/hotspot/os/posix/os_posix.cpp

bool os::is_interrupted(Thread* thread, bool clear_interrupted) {
  debug_only(Thread::check_for_dangling_thread_pointer(thread);)

  OSThread* osthread = thread->osthread();
  // 查看是否被中断
  bool interrupted = osthread->interrupted();

  // 清除标识位后再设置false
  if (interrupted && clear_interrupted) {
    osthread->set_interrupted(false);
  }

  return interrupted;
}

Java传递ClearInterrupted为false，对应C++的clear_interrupted

interrupted()

测试线程是否被中断，清除中断标识位

    public static boolean interrupted() {
        return currentThread().isInterrupted(true);
    }

简单的例子

public class MyThread45 {
    public static void main(String[] args) throws Exception
    {
        Runnable runnable = new Runnable()
        {
            public void run()
            {
                while (true)
                {
                    if (Thread.currentThread().isInterrupted())
                    {
                        System.out.println("线程被中断了");
                        return ;
                    }
                    else
                    {
                        System.out.println("线程没有被中断");
                    }
                }
            }
        };
        Thread t = new Thread(runnable);
        t.start();
        Thread.sleep(500);
        t.interrupt();
        System.out.println("线程中断了，程序到这里了");
    }
}

检查线程是否中断，中断线程，运行结果如下

······
线程没有被中断
线程没有被中断
线程没有被中断
线程被中断了
线程中断了，程序到这里了