CountDownLatch 多线程，等待所有线程结束

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);
构造方法参数指定了计数的次数
public void countDown();
当前线程调用此方法，则计数减一
public void await() throws InterruptedException
调用此方法会一直阻塞当前线程，直到计时器的值为0

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()));
            try {
                Thread.sleep(workTime);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                latch.countDown();
            }
            System.out.println("Worker " + workerName + " do work complete at " + sdf.format(new Date()));
 
        }
 
    }
 
}