countDownLatch.await(10, TimeUnit.SECONDS);使用案例

CountDownLatch.await(long timeout, TimeUnit unit) 方法可以让等待线程在指定的时间内等待其他线程完成任务，如果等待时间超过了指定时间，等待线程将会继续执行。这个方法比 CountDownLatch.await() 更加灵活，可以避免在某些情况下出现线程一直等待的情况。

以下是一个使用 CountDownLatch.await(long timeout, TimeUnit unit) 的案例：

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class CountDownLatchExample {
    public static void main(String[] args) throws InterruptedException {
        int taskCount = 3;
        CountDownLatch latch = new CountDownLatch(taskCount);

        Thread t1 = new Thread(new Task(latch, 5000));
        Thread t2 = new Thread(new Task(latch, 10000));
        Thread t3 = new Thread(new Task(latch, 15000));

        t1.start();
        t2.start();
        t3.start();

        boolean allTasksFinished = latch.await(10, TimeUnit.SECONDS);

        if (allTasksFinished) {
            System.out.println("All tasks have finished, now executing main task.");
        } else {
            System.out.println("Some tasks have not finished within the timeout period, now executing main task.");
        }
    }

    static class Task implements Runnable {
        private CountDownLatch latch;
        private long sleepTime;

        public Task(CountDownLatch latch, long sleepTime) {
            this.latch = latch;
            this.sleepTime = sleepTime;
        }

        @Override
        public void run() {
            try {
                System.out.println("Task started: " + Thread.currentThread().getName());
                Thread.sleep(sleepTime);
                System.out.println("Task finished: " + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                latch.countDown();
            }
        }
    }
}

在上面的例子中，我们创建了一个 CountDownLatch 对象并设置了计数器的初始值为 3。然后创建了 3 个线程分别执行不同时间的任务。在等待其他线程完成任务时，我们使用了 CountDownLatch.await(10, TimeUnit.SECONDS) 方法，表示等待 10 秒钟，如果其他线程在这个时间内没有完成任务，等待线程将会继续执行。当所有任务都执行完毕时，主任务将会开始执行。