CountDownLatch用于阻塞一个线程，等待其它线程先后到达某个条件的时候，再执行这个线程的后续操作。
public class CountDownLatchTest {
public static void main(String[] args) throws InterruptedException {
new CountDownLatchTest().go();
}
private void go() throws InterruptedException {
CountDownLatch countDownLatch = new CountDownLatch(3);
// 依次创建3个线程,并启动
new Thread(new Task(countDownLatch), "Thread1").start();
Thread.sleep(1000);
new Thread(new Task(countDownLatch), "Thread2").start();
Thread.sleep(1000);
new Thread(new Task(countDownLatch), "Thread3").start();
countDownLatch.await();
System.out.println("所有线程已到达,主线程开始执行" + System.currentTimeMillis());
}
class Task implements Runnable {
private CountDownLatch countDownLatch;
public Task(CountDownLatch countDownLatch) {
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
System.out.println("线程" + Thread.currentThread().getName() + "已经到达" + System.currentTimeMillis());
countDownLatch.countDown();
}
}
}
运行结果：
线程Thread1已经到达1488870269086
线程Thread2已经到达1488870270091
线程Thread3已经到达1488870271092
所有线程已到达,主线程开始执行1488870271093
可见，当Thread3到达以后，被阻塞的主线程立即开始执行，时间戳的微小差异，在于线程的调度的时间消耗。
