CountDownLatch

一个或多个线程等待其他线程完成操作后在在执行

CountDownLatch通过一个计数器来实现，await方法阻塞直到 countDown() 调用计数器归零之后释放所有等待的线程，并且任何后续的await调用立即返回。这是一次性现象 - 计数无法重置。如果您需要重置计数的版本，请考虑使用CyclicBarrier。

public class WorkerRunnable implements Runnable {

    private CountDownLatch countDownLatch;

    private int i;

    public WorkerRunnable(CountDownLatch latch, int i) {

        this.countDownLatch = latch;

        this.i = i;

    }

    @Override

    public void run() {

        doWork();

        this.countDownLatch.countDown();

    }

    private void doWork() {

        System.out.println("当前的线程: " + i);

    }

}

public class Client {

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

        final int n = 10;

        CountDownLatch doneSignal = new CountDownLatch(n);

        ExecutorService executor = Executors.newFixedThreadPool(10);

        for (int i = 0; i < n; i++) {

            executor.execute(new WorkerRunnable(doneSignal, i));

        }

        doneSignal.await();

        System.out.println("结束");

    }

}

out

当前的线程: 7

当前的线程: 6

当前的线程: 2

当前的线程: 1

当前的线程: 9

当前的线程: 0

当前的线程: 5

当前的线程: 4

当前的线程: 8

当前的线程: 3

结束