java并发性-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，但当我运行代码时，main方法永远不会返回。我知道alphonseThread和gastonThread都被以太锁住了，但是为什么不能从主线程中断它们？

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

但是为什么不能从主线程中断它们呢？

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

问题是，interrupt不会解除试图获取Java原语锁/互斥锁的线程的阻塞。事实上，我不认为有任何东西可以安全地解锁在原语锁上的线程。

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，而Lock.lockInterruptibly()方法...它将在线程被中断时解除阻塞。