JUC-CountDownLatch笔记

1.CountDownLatch简介
CountDownLatch是一个同步辅助类，完成指定线程数量之前，同步等待其他线程完成，个人感觉和计数器差不多。

2.CountDownLatch示例

import java.util.concurrent.CountDownLatch;

/**
 * Created by wuhao on 15-12-23.
 */
public class CountDownLatchDemo {
    public static void main(String[] args) {
        //计数器数值为3,工作线程数
        CountDownLatch countDownLatch=new CountDownLatch(3);
        WorkThread workThread1 = new WorkThread(1, 10, "张三", countDownLatch);
        WorkThread workThread2 = new WorkThread(2, 1, "李四", countDownLatch);
        WorkThread workThread3 = new WorkThread(3, 4, "王五", countDownLatch);
        workThread1.start();
        workThread2.start();
        workThread3.start();
        try {
            countDownLatch.await();
            System.out.println("All Thread Complete: ");
        } catch (InterruptedException e) {
            System.out.println("countDownLatch.await() Error");
        }
    }
}
class WorkThread extends Thread{
    private int index;
    private int time;
    private String name;
    private CountDownLatch countDownLatch;

    public WorkThread(int index, int time , String name, CountDownLatch countDownLatch) {
        this.index = index;
        this.time = time;
        this.name = name;
        this.countDownLatch = countDownLatch;
    }

    @Override
    public void run() {
        System.out.println("Thread Index: " + index + ", Name: " + name + " Start");
        try {
            Thread.sleep(time * 1000);
        } catch (InterruptedException e) {
            System.out.println("Thread.sleep(2000) Error");
        }
        System.out.println("Thread Index: " + index + ", Name: " + name + " End");
        countDownLatch.countDown(); //计数器-1
    }
}

输出结果:
1.计数器数值为3

Thread Index: 1, Name: 张三 Start
Thread Index: 2, Name: 李四 Start
Thread Index: 3, Name: 王五 Start
Thread Index: 2, Name: 李四 End
Thread Index: 3, Name: 王五 End
Thread Index: 1, Name: 张三 End
All Thread Complete: 
三个工作线程结束后触发

2.计数器数值为2

Thread Index: 1, Name: 张三 Start
Thread Index: 2, Name: 李四 Start
Thread Index: 3, Name: 王五 Start
Thread Index: 2, Name: 李四 End
Thread Index: 3, Name: 王五 End
All Thread Complete: 
Thread Index: 1, Name: 张三 End
两个工作线程结束后触发

3.计数器数值为4

Thread Index: 1, Name: 张三 Start
Thread Index: 2, Name: 李四 Start
Thread Index: 3, Name: 王五 Start
Thread Index: 2, Name: 李四 End
Thread Index: 3, Name: 王五 End
Thread Index: 1, Name: 张三 End
一直未触发