使主线程等待事件

Question

我正在做大学任务(坦率地说).问题是我应该在任何时候运行4个客户端线程(上升数字n).因此,当任何线程终止时,必须生成一个新线程.

  public static void main(String[] args) throws IOException,InterruptedException

   {
     /* some declarations.. */

     ClientThread client=new ClientThread ();

 Runnable intr =client;

 for(count=1;count<=number;count++)

 {
                 /* If 4 client threads has been spawned, wait until 1 of them exits */
           while(Thread.activeCount()<5) 
            ;
            new Thread(intr).start();
   }


       /* Wait until all other threads exits. */
       while(Thread.activeCount()!=1)
        ;   

 System.out.println("\n The sum of factorials is: "+client.getResult());
   }

我想删除忙碌的等待,因为它违背了我的程序的目的.我怎样才能制作主线程wait？(它显示的wait是非静态方法,不能从静态方法调用.)请帮忙.

Answer 1

java.util.concurrent中.CountDownLatch专为您的情况而设计.

限定 CountDownLatch doneSignal = new CountDownLatch(4);

doneSignal.await()将等到doneSignal.countDown()被召唤四次.所以让ClientThreads doneSignal在run()退出时调用相同的 引用doneSignal.countDown().

class ClientThread implements Runnable {
   private final CountDownLatch doneSignal;
   ClientThread (CountDownLatch doneSignal) {
      this.doneSignal = doneSignal;
   }
   public void run() {
      try {
        //Do something
        doneSignal.countDown();
      } catch (InterruptedException ex) {} 
   }
 }
...
//In main thread
doneSignal.await();

Answer 2

嗯 - 你必须手工做,还是你的老师希望你发现Executors.newFixedThreadPool(4)？

这正是具有四个工作线程的线程池所能完成的:不再有四个客户端并行运行,如果一个终止,则free'd工作线程已准备好"获得新工作".

这很简单:

public void test(int threads, int runnables) {
  ExecutorsService pool = Executors.newFixedThreadPool(threads);
  Runnable r = new Runnable() {
     public void run() {
       // calculate a factorial or do something else
       System.out.println(Thread.currenThread());
     }
  }
  for (int i = 0; i < runnables; i++)
    pool.execute(r);
}

让我们runnables大一点threads,你会从结果中看到最多threads数量的线程被(重新)用于执行runnables.