Java并发工具类：CountDownLatch与Semaphore实例

原创男娘i 2024-10-15 02:42 43阅读 0赞

在Java编程中，CountDownLatch和Semaphore是两种常用的并发控制工具。下面分别给出这两个工具的实例：

1. CountDownLatch

CountDownLatch用于协调多个线程的执行顺序。当它的计数器初始值大于0时，线程会一直等待，直到计数器归零。

实例：

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

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

public void workerThread(int index) {
        try {
            System.out.println("Worker " + index + " starting...");
            Thread.sleep(index * 100); // simulate work
            System.out.println("Worker " + index + " finished.");
            countDownLatch.countDown(); // signal completion
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

public static void main(String[] args) throws InterruptedException {
        CounterExample counterExample = new CounterExample();

// 创建3个线程
        for (int i = 0; i < 3; i++) {
            Thread workerThread = new Thread(counterExample::workerThread, "Worker " + i));
            workerThread.start();
        }

// 等待所有任务完成
        countDownLatch.await(); // wait until all workers have finished

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

2. Semaphore

Semaphore是一种多路共享资源的机制，它用于控制同时访问某个资源的线程数量。当信号量的值大于0时，允许新的请求进入；当值等于0时，阻止新的请求进入。

实例：

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

public class SemaphoreExample {
    private final Semaphore semaphore = new Semaphore(2); // allow 2 threads to access the resource

public void workerThread() throws InterruptedException {
        System.out.println("Worker starting...");
        semaphore.acquire(); // wait for permission to access the resource
        try {
            // Access shared resource here...
            Thread.sleep(500); // simulate work
        } finally {
            semaphore.release(); // signal completion and release permission
            System.out.println("Worker finished.");
        }
    }

public static void main(String[] args) throws InterruptedException {
        SemaphoreExample semaphoreExample = new SemaphoreExample();

// 创建1个线程
        Thread workerThread = new Thread(semaphoreExample::workerThread));
        workerThread.start();
    }
}
```

总结，CountDownLatch和Semaphore都是Java并发工具类的一部分，它们在多线程环境下管理资源的访问，确保线程的同步与协调。