downSingal 的作用是什么 类似一个阻塞锁吗
import java.util.Random;
import java.util.concurrent.CountDownLatch;

class Driver { // ...
  public static void main(String[] argus) throws InterruptedException {
     CountDownLatch startSignal = new CountDownLatch(1);
     CountDownLatch doneSignal = new CountDownLatch(3);

     for (int i = 0; i < 3; ++i) // create and start threads
       new Thread(new Worker2(startSignal, doneSignal)).start();

   System.out.println(Thread.currentThread().getName()+1);            // don't let run yet
     startSignal.countDown();      // let all threads proceed
     Thread.sleep(new Random().nextInt(3000));
  System.out.println(Thread.currentThread().getName()+2);
//  doneSignal.countDown();
//  doneSignal.countDown();
//  doneSignal.countDown();
     doneSignal.await();           // wait for all to finish  在此处堵塞，只有计数器减为零才继续
     System.out.println("over");
   }
}

class Worker2 implements Runnable {
   private final CountDownLatch startSignal;
   private final CountDownLatch doneSignal;
   Worker2(CountDownLatch startSignal, CountDownLatch doneSignal) {
      this.startSignal = startSignal;
      this.doneSignal = doneSignal;
   }
   public void run() {
      try {
        startSignal.await();
        Thread.sleep(new Random().nextInt(3000));
        doWork();
        doneSignal.countDown();
} catch (InterruptedException ex) {} // return;
   }

   void doWork() { System.out.println(Thread.currentThread().getName()+3); }
}

1. import java.util.Random;
   
2. import java.util.concurrent.CountDownLatch;
   
3. 
   
4. class Driver { // ...
   
5.   public static void main(String[] argus) throws InterruptedException {
   
6.      CountDownLatch startSignal = new CountDownLatch(1);
   
7.      CountDownLatch doneSignal = new CountDownLatch(3);
   
8. 
   
9.      for (int i = 0; i < 3; ++i) // create and start threads
   
10.        new Thread(new Worker2(startSignal, doneSignal)).start();
    
11. 
    
12.    System.out.println(Thread.currentThread().getName()+1);            // don't let run yet
    
13.      startSignal.countDown();      // let all threads proceed
    
14.      Thread.sleep(new Random().nextInt(3000));
    
15.   System.out.println(Thread.currentThread().getName()+2);
    
16. //  doneSignal.countDown();
    
17. //  doneSignal.countDown();
    
18. //  doneSignal.countDown();
    
19.      doneSignal.await();           // wait for all to finish  在此处堵塞，只有计数器减为零才继续
    
20.      System.out.println("over");
    
21.    }
    
22. }
    
23. 
    
24. class Worker2 implements Runnable {
    
25.    private final CountDownLatch startSignal;
    
26.    private final CountDownLatch doneSignal;
    
27.    Worker2(CountDownLatch startSignal, CountDownLatch doneSignal) {
    
28.       this.startSignal = startSignal;
    
29.       this.doneSignal = doneSignal;
    
30.    }
    
31.    public void run() {
    
32.       try {
    
33.         startSignal.await();
    
34.         Thread.sleep(new Random().nextInt(3000));
    
35.         doWork();
    
36.         doneSignal.countDown();
    
37. } catch (InterruptedException ex) {} // return;
    
38.    }
    
39. 
    
40.    void doWork() { System.out.println(Thread.currentThread().getName()+3); }
    
41. }
    

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downSingal 还是 doneSignal？没找着downSingal啊，doneSingal是Worker2三个线程干完自己的事通知主线程可以继续向下走了