CountDownLatch的使用

CountDownLatch，一个同步辅助类，在完成一组正在其他线程中执行的操作之前，它允许一个或多个线程一直等待。
主要方法
public CountDownLatch(int count);
public void countDown();
public void await() throws InterruptedException

public CountDownLatch(int count);在构造器中传入count值，表示需要等待被执行完成的线程/任务数目。
countDown() 当某一个线程执行完相应的操作后，调用countDown()标示这个操作已经完成。
await() ,通过调用await()声明当线程需要等待其他任务执行完成后才可以进行后续操作。

public class CountDownLatchDemo {

    final static SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    public static void main(String[] args) throws InterruptedException {

        CountDownLatch latch=new CountDownLatch(2);//两个工人的协作

        Worker worker1=new Worker("zhang san", 5000, latch);

        Worker worker2=new Worker("li si", 8000, latch);

        worker1.start();//

        worker2.start();//

        latch.await();//等待所有工人完成工作

        System.out.println("all work done at "+sdf.format(new Date()));

    }

    

    

    static class Worker extends Thread{

        String workerName; 

        int workTime;

        CountDownLatch latch;

        public Worker(String workerName ,int workTime ,CountDownLatch latch){

             this.workerName=workerName;

             this.workTime=workTime;

             this.latch=latch;

        }

        public void run(){

            System.out.println("Worker "+workerName+" do work begin at "+sdf.format(new Date()));

            doWork();//工作了

            System.out.println("Worker "+workerName+" do work complete at "+sdf.format(new Date()));

            latch.countDown();//工人完成工作，计数器减一

        }

        

        private void doWork(){

            try {

                Thread.sleep(workTime);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

        }

    }

    

     

}