java编程思想-CountDownLatch

最新推荐文章于 2025-08-09 15:58:26 发布

asdfg19

最新推荐文章于 2025-08-09 15:58:26 发布

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文章标签： java

本文链接：https://blog.youkuaiyun.com/asdfg19/article/details/84297515

本文详细解析了CountDownLatch在并发编程中的使用方法，包括其构造、工作原理及在多任务执行中的作用。通过代码示例展示了如何利用CountDownLatch实现任务之间的同步与等待，以确保在某个任务完成之前，所有依赖此任务的任务不会被提前执行。

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thinking in java的代码，关于CountDownLatch的部分。CountDownLatch实例化的时候在构造函数中会填写一个数字SIZE（计数器），通过调用countDown()，每次会将计数器减1，直到等于0，这个时候，才会改变await的阻塞状态。
SIZE等于1，可以模拟开关，等于N可以模拟执行某一个步骤前的N个步骤。
代码1：

package com.cakushin.thread.countdownlatch;

import java.util.Random;
import java.util.concurrent.CountDownLatch;

public class TaskPortion implements Runnable {
	private static int counter = 0;
	private final int id = counter++;
	private static Random rand = new Random(47);
	private final CountDownLatch latch;
	
	public TaskPortion(CountDownLatch latch){
		this.latch = latch;
	}

	@Override
	public void run() {
		try {
			doWork();
			latch.countDown();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

	private void doWork() throws InterruptedException {
		Thread.sleep(rand.nextInt(2000));
		System.out.println(this + " completed!");
	}
	
	public String toString(){
		return String.format("%1$-3d", id);
	}

}

代码2：

package com.cakushin.thread.countdownlatch;

import java.util.concurrent.CountDownLatch;

public class WaitingTask implements Runnable {
	private static int counter = 0;
	private final int id = counter++;
	private final CountDownLatch latch;
	
	public WaitingTask(CountDownLatch latch){
		this.latch = latch;
	}

	@Override
	public void run() {
		try {
			latch.await();
			System.out.println("Latch barrier passed for " + this);
		} catch (InterruptedException e) {
			System.out.println(this + " interrupted");
		}
	}
	
	public String toString(){
		return String.format("WatingTask %1$-3d", id);
	}

}

代码3：

package com.cakushin.thread.countdownlatch;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public final class CountDownLatchDemo {

	static final int SIZE = 100;
	
	/**
	 * @author Administrator
	 * @param args
	 */
	public static void main(String[] args) {
		ExecutorService exec = Executors.newCachedThreadPool();
		CountDownLatch latch = new CountDownLatch(SIZE);
		for(int i = 0; i < 10; i++){
			exec.execute(new WaitingTask(latch));
		}
		for(int i = 0; i < 100; i++){
			exec.execute(new TaskPortion(latch));
		}
		System.out.println("Launched all tasks");
		exec.shutdown();
	}

}