CountDownLatch，一個同步輔助類，在完成一組正在其他線程中執行的操作之前，它允許一個或多個線程一直等待。
主要方法
public CountDownLatch(int count);
public void countDown();
public void await() throws InterruptedException
構造方法參數指定了計數的次數
countDown方法，當前線程調用此方法，則計數減一
awaint方法，調用此方法會一直阻塞當前線程，直到計時器的值為0
例子
java代碼
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);//兩個工人的協作 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，計數器減一 } private void doWork(){ try { Thread.sleep(workTime); } catch (InterruptedException e) { e.printStackTrace(); } } } }
輸出：
Worker zhang san do work begin at 2011-04-14 11:05:11Worker li si do work begin at 2011-04-14 11:05:11Worker zhang san do work complete at 2011-04-14 11:05:16Worker li si do work complete at 2011-04-14 11:05:19all work done at 2011-04-14 11:05:19
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