JAVA 多线程编程之CountDownLatch使用详解

CountDownLatch latch = new CountDownLatch(3); // 初始计数值为 3

Runnable task = new Runnable() {
    @Override
    public void run() {
        // 线程任务逻辑
        // ...
        latch.countDown(); // 完成任务后调用 countDown()
    }
};

try {
    latch.await(); // 等待计数器的值变成 0
    // 继续执行需要等待的线程后续逻辑
} catch (InterruptedException e) {
    // 处理中断异常
    e.printStackTrace();
}

import java.util.concurrent.CountDownLatch;

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

        // 创建并启动三个工人线程
        for (int i = 0; i < workerCount; i++) {
            Worker worker = new Worker(latch, "Worker " + (i + 1));
            new Thread(worker).start();
        }

        try {
            System.out.println("Main thread is waiting for workers to finish...");
            latch.await(); // 主线程等待三个工人线程完成任务
            System.out.println("All workers have finished, main thread continues...");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    static class Worker implements Runnable {
        private final CountDownLatch latch;
        private final String name;

        public Worker(CountDownLatch latch, String name) {
            this.latch = latch;
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + " starts working...");
            // 模拟工作耗时
            try {
                Thread.sleep((long) (Math.random() * 10000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(name + " finishes working.");
            latch.countDown(); // 工人完成任务后调用 countDown()
        }
    }
}

public static void main(String[] args) throws InterruptedException {
    final int workerCount = 3;
    final CountDownLatch latch = new CountDownLatch(workerCount);
    System.out.println("Main thread is waiting for workers to finish...");
    // 创建并启动三个工人线程
    for (int i = 0; i < workerCount; i++) {
        Worker worker = new Worker(latch, "Worker " + (i + 1));
        Thread t = new Thread(worker);
        t.start();
        t.join(); // 等待上一个线程执行完成
    }
    try {
        latch.await(); // 主线程等待三个工人线程完成任务
        System.out.println("All workers have finished, main thread continues...");
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}