Java并发编程：CountDownLatch和CyclicBarrier实例

原创心已赠人 2024-10-09 08:06 47阅读 0赞

在Java的并发编程中，CountDownLatch和CyclicBarrier是两种常见的同步工具。它们用于协调多个线程的执行顺序。

1. CountDownLatch

CountDownLatch最初是用来在一个或多个线程等待一组相关操作完成的。当一个计数器下降到0时，所有等待它的线程都将被唤醒。

示例：

```java
import java.util.concurrent.CountDownLatch;

public class CountDownLatchExample {
    public static void main(String[] args) throws InterruptedException {
        // 创建CountDownLatch实例，初始值为3
        CountDownLatch countDownLatch = new CountDownLatch(3);

// 定义三个线程，每个线程调用countDown方法减小计数器的值
        Thread thread1 = new Thread(() -> countDownLatch.countDown()));
        Thread thread2 = new Thread(() -> countDownLatch.countDown()));
        Thread thread3 = new Thread(() -> countDownLatch.countDown()));

// 启动所有线程
        thread1.start();
        thread2.start();
        thread3.start();

// 等待所有计数器都降为0，表明所有线程已完成任务
        countDownLatch.await();
        
        System.out.println("All threads have completed their tasks.");
    }
}
```

2. CyclicBarrier

CyclicBarrier用于协调一组等待其关闭的线程。当一个屏障打开时，所有等待它的线程都将获得一个机会来执行代码。

示例：

```java
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierExample {
    public static void main(String[] args) throws InterruptedException {
        // 创建CyclicBarrier实例，初始值为2
        CyclicBarrier cyclicBarrier = new CyclicBarrier(2);

// 定义两个线程，每个线程调用await方法等待屏障打开
        Thread thread1 = new Thread(() -> {
            try {
                cyclicBarrier.await();
                System.out.println("Thread 1 reached the barrier.");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }});

Thread thread2 = new Thread(() -> {
            try {
                cyclicBarrier.await();
                System.out.println("Thread 2 reached the barrier.");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }});

// 启动所有线程
        thread1.start();
        thread2.start();

// 等待屏障关闭，所有等待它的线程都将执行完代码
        cyclicBarrier.await();

System.out.println("All threads have completed their tasks.");
    }
}
```

这两个工具在Java并发编程中常常被用来控制线程的执行顺序。