为什么java中的Countdownlatch不能停止在给定的锁存计数？(why can't Countdownlatch in java stops at given latch count?)

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

class Processor implements Runnable {
    private CountDownLatch latch;

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

    public void run() {
        System.out.println("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(5); // coundown from 5 to 0

        ExecutorService executor = Executors.newFixedThreadPool(2); // 2 Threads in pool

        for(int i=0; i < 10; i++) {
            executor.submit(new Processor(latch)); // ref to latch. each time call new Processes latch will count down by 1
        }

        try {
            latch.await();  // wait until latch counted down to 0
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("Completed.");
    }

}
 
 输出： 
 
 入门入门入门入门入门入门已完成入门入门入门 
 
 在上面的代码中，当“闩锁计数下降到5-0”时，“已完成”应该打印6次，为什么总是第7次或第8次？ 我理解错了吗？ 

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

class Processor implements Runnable {
    private CountDownLatch latch;

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

    public void run() {
        System.out.println("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(5); // coundown from 5 to 0

        ExecutorService executor = Executors.newFixedThreadPool(2); // 2 Threads in pool

        for(int i=0; i < 10; i++) {
            executor.submit(new Processor(latch)); // ref to latch. each time call new Processes latch will count down by 1
        }

        try {
            latch.await();  // wait until latch counted down to 0
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("Completed.");
    }

}
 
Output: 
 
Started Started Started Started Started Started Started Completed` Started Started Started
 
In the above code "Completed" should be printed after 6 times "Started" as latch count downs to 5 - 0, why it is always 7th or 8th time? Have i understood wrong?

原文：https://stackoverflow.com/questions/50628056