1

我目前有这个运行方法，我希望 3 个单独的线程访问并等待另一个线程通知。

public void run(){
   try {
      System.out.println(this.name + " waits on the table...");
      /// waits for agent to signal that new ingredients have been passed out
      wait();
   } catch(InterruptedException ex) {
      Thread.currentThread().interrupt();
   }
   System.out.println(this.name + " stops waiting and checks the table...");
   checkTable();
}

目前这会抛出一个java.lang.IllegalMonitorStateException可以通过在方法上使用同步来解决的问题。问题是当我使用同步时，第一个线程将等待，而其他两个线程无法执行任何操作，因为第一个线程对该方法具有锁定。所以我的问题是我怎样才能让三个单独的线程可以访问这个方法并同时等待？

4

2 回答 2

3

要使用wait()您必须拥有显示器。 您通过使用获得所有权synchronize。在你的情况下synchronize(this)。

但是要阻止 3 个线程并从第 4 个线程释放它们，您可以使用java.util.concurrent.CyclicBarrier或Perceptionjava.util.concurrent.CountDownLatch提到的

这是一个带有 CyclicBarrier 的版本：

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class RendezVous extends Thread {

   private final CyclicBarrier _barrier;

   RendezVous( String name, CyclicBarrier barrier ) {
      super( name );

      _barrier = barrier;
      setDaemon( true );
      start();
   }

   @Override public void run() {
      System.out.println( getName() + " waits for counterparts..." );
      try { _barrier.await(); }
      catch( InterruptedException | BrokenBarrierException x ) {
         x.printStackTrace(); }
      System.out.println( getName() + " has reached its rendez-vous!");
   }

   public static void main( String[] args ) throws InterruptedException {
      CyclicBarrier barrier = new CyclicBarrier( 4 );
      new RendezVous( "Rdvz 1", barrier ); Thread.sleep(  1000L );
      new RendezVous( "Rdvz 2", barrier ); Thread.sleep(  1000L );
      new RendezVous( "Rdvz 3", barrier ); Thread.sleep(  1000L );
      new RendezVous( "Rdvz 4", barrier ); Thread.sleep( 10000L );
   }
}

输出：

Rdvz 1 waits for counterparts...
Rdvz 2 waits for counterparts...
Rdvz 3 waits for counterparts...
Rdvz 4 waits for counterparts...
Rdvz 4 has reached its rendez-vous!
Rdvz 1 has reached its rendez-vous!
Rdvz 2 has reached its rendez-vous!
Rdvz 3 has reached its rendez-vous!

还有一个带有 CountDownLatch 的版本：

import java.util.concurrent.CountDownLatch;

public class CountDownLatchDemo extends Thread {

   private final CountDownLatch _cdl;

   CountDownLatchDemo( String name, CountDownLatch cdl ) {
      super( name );

      _cdl = cdl;
      setDaemon( true );
      start();
   }

   @Override public void run() {
      System.out.println( getName() + " waits for counterparts..." );
      try {
         _cdl.countDown();
         _cdl.await();
      }
      catch( InterruptedException x ) {
         x.printStackTrace(); }
      System.out.println( getName() + " has reached its rendez-vous!");
   }

   public static void main( String[] args ) throws InterruptedException {
      CountDownLatch cdl = new CountDownLatch( 4 );
      new CountDownLatchDemo( "Rdvz 1", cdl ); Thread.sleep(  1000L );
      new CountDownLatchDemo( "Rdvz 2", cdl ); Thread.sleep(  1000L );
      new CountDownLatchDemo( "Rdvz 3", cdl ); Thread.sleep(  1000L );
      new CountDownLatchDemo( "Rdvz 4", cdl ); Thread.sleep( 10000L );
   }
}

输出：

Rdvz 1 waits for counterparts...
Rdvz 2 waits for counterparts...
Rdvz 3 waits for counterparts...
Rdvz 4 waits for counterparts...
Rdvz 4 has reached its rendez-vous!
Rdvz 1 has reached its rendez-vous!
Rdvz 2 has reached its rendez-vous!
Rdvz 3 has reached its rendez-vous!
于 2013-02-23T08:05:07.217 回答
0

当第一个线程等待时，它会释放锁。所以其他线程可以获取锁

于 2013-02-23T08:08:18.953 回答