为什么我的线程没有完成(Why my threads are not completing)

 我想了解countDownLatch，我有这个程序，但我不知道为什么我的程序没有返回而没有完成。 
 
package countDownLatches;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class Processor implements Runnable {

    CountDownLatch latch;

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

    public void run() {
        System.out.println("thread started: ");
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        latch.countDown();
    }

}

public class App {
    public static void main(String args[]) {
        CountDownLatch latch = new CountDownLatch(3);
        ExecutorService executorService = Executors.newFixedThreadPool(3);
        for (int i = 0; i < 3; i++) {
            executorService.submit(new Processor(latch));
        }
        try {
            latch.await();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("task completed");
    }
}

I am trying to understand countDownLatch and I have this program but I do not know why my program is not returning and not finishing. 
 
package countDownLatches;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class Processor implements Runnable {

    CountDownLatch latch;

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

    public void run() {
        System.out.println("thread started: ");
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        latch.countDown();
    }

}

public class App {
    public static void main(String args[]) {
        CountDownLatch latch = new CountDownLatch(3);
        ExecutorService executorService = Executors.newFixedThreadPool(3);
        for (int i = 0; i < 3; i++) {
            executorService.submit(new Processor(latch));
        }
        try {
            latch.await();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("task completed");
    }
}

原文：https://stackoverflow.com/questions/22439547