Java多线程同步工具：Semaphore与CountDownLatch实践示例-蒲公英云

Java多线程同步工具：Semaphore与CountDownLatch实践示例

Semaphore和CountDownLatch是Java中常用的多线程同步工具。它们主要用来控制同时访问资源的线程数量。

Semaphore（信号量）

Semaphore是一种二值信号机制，它维护一个当前值。当一个工作者试图获取信号量时，如果当前值大于0，那么就减少1，工作者获得信号；否则工作者等待，直到信号量释放。

示例代码：

import java.util.concurrent.Semaphore;
public class SemaphoreExample {
    private Semaphore semaphore = new Semaphore(2); // 初始化信号量为2
    public void workerThread() throws InterruptedException {
        try {
            semaphore.acquire(); // 获取信号
            System.out.println("Worker " + (threadId++) + " is running ...");
            // 工作逻辑
            Thread.sleep(3000);
            System.out.println("Worker " + (threadId++) + " finished its task ...");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            semaphore.release(); // 释放信号量
        }
    }
    public static void main(String[] args) throws InterruptedException {
        SemaphoreExample example = new SemaphoreExample();
        for (int i = 0; i < 4; i++) { // 创建4个线程实例
            Thread workerThread = new Thread(example::workerThread, "Worker " + (i+1))));
            workerThread.start(); // 启动线程
        }
    }
}

CountDownLatch（计数器）

CountDownLatch是一个特殊的共享变量，它可以被初始化为一个给定的值。当一个工作者需要等待其他工作者完成特定操作后才能开始执行时，可以使用CountDownLatch。

示例代码：

import java.util.concurrent.CountDownLatch;
public class CountDownLatchExample {
    private CountDownLatch countDownLatch = new CountDownLatch(2); // 初始化计数器为2
    public void workerThread() throws InterruptedException {
        try {
            countDownLatch.await(); // 等待计数器减少到0
            System.out.println("Worker " + (threadId++) + " is running ...");
            // 工作逻辑
            Thread.sleep(3000);
            System.out.println("Worker " + (threadId++) + " finished its task ...");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws InterruptedException {
        CountDownLatchExample example = new CountDownLatchExample();
        for (int i = 0; i < 4; i++) { // 创建4个线程实例
            Thread workerThread = new Thread(example::workerThread, "Worker " + (i+1))));
            workerThread.start(); // 启动线程
        }
        countDownLatch.countDown(); // 计数器减少到0，表示所有工作已完成
    }
}