CountDownLatch中await（）的用途是什么？(What is the purpose of await() in CountDownLatch?)

 我有下面的程序，我使用java.util.concurrent.CountDownLatch，而不使用await（）方法它的工作正常。 我是并发新手，想知道await（）的用途。 在“CyclicBarrier”中我能理解为什么await（）是需要的，但为什么在“CountDownLatch”中呢？ 
 
 程序， 
 
 类CountDownLatchSimple 
 
public static void main(String args[]) {
  CountDownLatch latch = new CountDownLatch(3);
  Thread one = new Thread(new Runner(latch),"one");
  Thread two = new Thread(new Runner(latch), "two");
  Thread three = new Thread(new Runner(latch), "three");

  // Starting all the threads
  one.start(); two.start(); three.start();

}
 
 类Runner实现Runnable 
 
CountDownLatch latch;

public Runner(CountDownLatch latch) {
    this.latch = latch;
}

@Override
public void run() {
    System.out.println(Thread.currentThread().getName()+" is Waiting.");
    try {
        Thread.sleep(2000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    latch.countDown();
    System.out.println(Thread.currentThread().getName()+" is Completed.");
}
 
 输出二是等待。 三是等待。 一个是等待。 一个是已完成。 两个已完成。 三是完成。 

I have the following program, where I am using java.util.concurrent.CountDownLatch and without using await() method its working fine. I am new to concurrency and want to know the purpose of await(). In "CyclicBarrier" I can understand why await() is needed but why in "CountDownLatch"?
 
Program,
 
class CountDownLatchSimple 
 
public static void main(String args[]) {
  CountDownLatch latch = new CountDownLatch(3);
  Thread one = new Thread(new Runner(latch),"one");
  Thread two = new Thread(new Runner(latch), "two");
  Thread three = new Thread(new Runner(latch), "three");

  // Starting all the threads
  one.start(); two.start(); three.start();

}
 
class Runner implements Runnable
 
CountDownLatch latch;

public Runner(CountDownLatch latch) {
    this.latch = latch;
}

@Override
public void run() {
    System.out.println(Thread.currentThread().getName()+" is Waiting.");
    try {
        Thread.sleep(2000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    latch.countDown();
    System.out.println(Thread.currentThread().getName()+" is Completed.");
}
 
OUTPUT two is Waiting. three is Waiting. one is Waiting. one is Completed. two is Completed. three is Completed.

原文：https://stackoverflow.com/questions/41866691