Java中并发工具库：CountDownLatch和Semaphore应用示例

原创绝地灬酷狼 2024-10-07 05:09 79阅读 0赞

在Java中，CountDownLatch和Semaphore是两个常用的并发控制工具。下面分别给出它们的应用示例。

1. CountDownLatch（倒计时）

CountDownLatch用于协调多个线程的执行顺序。当它的初始值为n（表示等待的线程数量）时，每个线程都会调用await()方法进行等待。

应用示例：

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

public class CountDownLatchExample {
    private final CountDownLatch countDownLatch = new CountDownLatch(3);

public void startThreads() {
        Thread thread1 = new Thread(() -> countDownLatch.countDown()));
        Thread thread2 = new Thread(() -> countDownLatch.countDown()));
        Thread thread3 = new Thread(() -> countDownLatch.countDown()));

thread1.start();
        thread2.start();
        thread3.start(); // 这里会等待所有线程完成
    }

public static void main(String[] args) {
        CountDownLatchExample example = new CountDownLatchExample();
        example.startThreads();
        try {
            if (example.countDownLatch.await(5, TimeUnit.SECONDS))) {
                System.out.println("All threads finished.");
            } else {
                System.out.println("Timeout occurred.");
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
```

2. Semaphore（信号量）

Semaphore是一种线程同步工具，用于控制对共享资源的访问。它的值可以是0表示无资源可用，也可以是非0表示有资源可用。

应用示例：

```java
import java.util.concurrent.Semaphore;

public class SemaphoreExample {
    private final Semaphore semaphore = new Semaphore(2);

public void startThreads() {
        Thread thread1 = new Thread(() -> semaphore.acquire()));
        Thread thread2 = new Thread(() -> semaphore.acquireIfPresent()));

thread1.start();
        thread2.start(); // 这里会等待所有线程完成
    }

public static void main(String[] args) {
        SemaphoreExample example = new SemaphoreExample();
        example.startThreads();
        try {
            if (example.semaphore.tryAcquire(5, TimeUnit.SECONDS)))) {
                System.out.println("All threads finished.");
            } else {
                System.out.println("Timeout occurred.");
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
```

以上就是CountDownLatch和Semaphore在Java中的简单应用示例。