等待多线程完成

CountDownLatch

private static void countDownLatch() throws InterruptedException {
        int length = 100;
        CountDownLatch latch = new CountDownLatch(length);

        Long t1 = System.nanoTime();
        List<Integer> results = new ArrayList<>();
        for (int index = 0; index < length; index++) {
            final int threadIndex = index;
            Thread thread = new Thread(() -> {
                System.out.println("start thread - " + threadIndex);
                Double random = -1.0;
                try {
                    Thread.sleep(1 * 1000);
                    random = (100 * Math.random());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("stop thread - " + threadIndex + " random = " + random.intValue());
                results.add(random.intValue());
                latch.countDown();

            });
            thread.start();
        }

        // 注意：CountDownLatch要加上这段才生效，原因见下面文字描述
        latch.await();

        System.out.println("跑完了...");
        Long t2 = System.nanoTime();
        System.out.println(results);
        System.out.println("time = " + (t2 - t1));
    }

CountDownLatch的构造函数接受一个int类型的参数作为计数器，如果你想等待N个节点（N个Thread 如上述示例 ），这里就传入N

CountDownLatch.countDown()

调用CountDownLatch.countDown() ，N就会减1

CountDownLatch.wait()

CountDownLatch.wait()会阻塞当前线程，直到N变成零

当某个线程处理的特别慢时，如果不需要主线程一直等待下去，可以使用另外一个重载的wait(long time,TimeUnit unit),这个方法等待指定时间后就不再阻塞线程了

链接：https://www.jianshu.com/p/00d0fcdeb7df

来源：oschina

链接：https://my.oschina.net/u/937111/blog/4728914