CountDownLatch用法

CountDownLatch是Java中提供的一个同步工具类，它可以用来控制一个或多个线程等待多个线程的操作完成。

CountDownLatch的用法如下：

1. 创建一个CountDownLatch对象，指定需要等待的线程数。

CountDownLatch latch = new CountDownLatch(5);

2. 每个需要等待的线程执行完后调用CountDownLatch的countDown方法减少计数器。

latch.countDown();

3. 等待所有线程执行完毕后，调用CountDownLatch的await方法进行等待。

latch.await();

4. 在所有线程执行完毕后，主线程或其他线程可以继续执行自己的操作。

示例代码：

import java.util.concurrent.CountDownLatch;

public class CountDownLatchDemo {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(5);

        for (int i = 0; i < 5; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + " is working...");
                try {
                    // 模拟线程执行时间
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " done");
                latch.countDown();
            }).start();
        }

        System.out.println("Waiting for all threads to finish...");
        latch.await();
        System.out.println("All threads have finished, continue to execute the main thread.");
    }
}

运行结果：

Waiting for all threads to finish...
Thread-0 is working...
Thread-2 is working...
Thread-1 is working...
Thread-3 is working...
Thread-4 is working...
Thread-1 done
Thread-3 done
Thread-0 done
Thread-2 done
Thread-4 done
All threads have finished, continue to execute the main thread.