CountDownLatch浅析

CountDownLatch类是一个同步计数器,构造时传入int参数,该参数就是计数器的初始值，每调用一次countDown()方法，计数器减1,计数器大于0 时，await()方法会阻塞程序继续执行。

CountDownLatch可以看作是一个倒计数的锁存器，当计数减至0时触发特定的事件。利用这种特性，可以让主线程等待子线程的结束

使用场景：有一个任务想要往下执行，但必须要等到其他的任务执行完毕后才可以继续往下执行。

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);
        Worker worker1=new Worker("zhang san", 5000, latch);
        Worker worker2=new Worker("li si", 8000, latch);
        worker1.start();
        worker2.start();
        latch.await();
        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();
            System.out.println("Worker "+workerName+" do work complete at "+sdf.format(new Date()));

        }
        
        private void doWork(){
            try {
                Thread.sleep(workTime);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                latch.countDown();
            }
        }
    }
    
}
                                

 

参考：

      http://www.iteye.com/topic/1002652

      http://www.cnblogs.com/whgw/archive/2011/09/29/2195827.html