java 并发 - 中断 DeadLook 线程

Question

我正在尝试学习 java 并发的基础知识，我从 oracle java 教程开始直到 http://docs.oracle.com/javase/tutorial/essential/concurrency/deadlock.html ，我只是在代码示例中添加了一些行，但是当我运行代码时，main 方法永远不会返回。 我知道 alphonseThread 和 gastonThread 都被 ether 死锁了，但是为什么不能从主线程中中断它们呢？

public class DeadLock {

     static class Freind {

          private final String name;
          public Freind(String name_) {
               this.name = name_;
          }

          public String getName() {
               return this.name;
          }

          public synchronized void bow(Freind bower) throws InterruptedException {
                System.out.format("%s : %s " + "has bowed to me!%n",
                      this.name, bower.getName());
                Thread.sleep(2000);
                bower.bowBack(this);

         }

         public synchronized void bowBack(Freind bower) {
               System.out.format("%s : %s " + "has bowed back to me!%n",
                this.name, bower.getName());
         }
     }

    @SuppressWarnings("SleepWhileInLoop")
    public static void main(String[] args) throws InterruptedException {
        // wait for 4 seconds before send a interuption signal
        int patient = 4000;
        int waitingUnit = 1000;
        long start;
        final Freind alphonse = new Freind("Alphonse");
        final Freind gaston = new Freind("Gaston");
        // the first thread 
        Thread alphonseThread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    alphonse.bow(gaston);
                } catch (InterruptedException ex) {
                    System.out.println("Alphnso have been killed");
                }
             }
        });
        // the second thread
        Thread gastonThread = new Thread(new Runnable() {
            @Override
            public void run() {
                 try {
                     gaston.bow(alphonse);
                 } catch (InterruptedException ex) {
                     System.out.println("Gaston have been killed ");
                 }
             }
         });
         // start the tow threads                
         start = System.currentTimeMillis();
         alphonseThread.start();
         gastonThread.start();
         while (alphonseThread.isAlive() || gastonThread.isAlive()) {
             if (((System.currentTimeMillis() - start) < patient)
                     && (alphonseThread.isAlive() || gastonThread.isAlive())) {
                 System.out.println(System.currentTimeMillis() - start);
                 System.out.println("still waiting !!");
                 Thread.sleep(waitingUnit);
              } else {
                 if (alphonseThread.isAlive()) {
                     alphonseThread.interrupt();
                     alphonseThread.join();
                 }
                 if (gastonThread.isAlive()) {
                     gastonThread.interrupt();
                     gastonThread.join();
                }                     
             }
         }
         System.out.println("finnaly I kill all of them");
     }
 }

Answer 1

but why can't interrupt them from the main Thread?

您可以从主线程(或任何地方)中断。只需在要中断的线程上调用 Thread.interrupt()。

问题是 interrupt 不会解除阻塞试图获取 Java 原始锁/互斥锁的线程。事实上，我认为没有任何东西可以安全地解除阻塞在原始​​锁上死锁的线程。

如果您希望您的应用程序能够从涉及对象锁的死锁中恢复，那么您可能应该使用Lock 对象，并且 Lock.lockInterruptibly()方法 ... 当线程被中断时，它将解除阻塞。