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()));

}

}

}