【高并发系列】13、倒计数器 CountDownLatch

java.util.concurrent.CountDownLatch用来控制线程等待，让指定线程等待直到计数结束再开始执行；

火箭发射前倒计时，main方法等待10个检查线程都检查完毕后，再执行发射；

public class CountDownLatchDemo implements Runnable {
	private static final CountDownLatch COUNT_DOWN_LATCH = new CountDownLatch(10);
	private static final CountDownLatchDemo DEMO = new CountDownLatchDemo();
	@Override
	public void run() {
		try {
			TimeUnit.SECONDS.sleep(new Random().nextInt(10));
			System.out.println(Thread.currentThread().getName() + " check complete.");
			COUNT_DOWN_LATCH.countDown();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	public static void main(String[] args) throws InterruptedException {
		ExecutorService exec = Executors.newFixedThreadPool(10);
		for(int i = 0; i < 10; i++) {
			exec.submit(DEMO);
		}
		COUNT_DOWN_LATCH.await();
		System.out.println("Fire!");
		exec.shutdown();
	}
}