Java-CountDownLatch的小例子

内容：CountDownLatch允许一个或多个线程等待其他线程完成操作。CountDownLatch的构造函数接收一个int类型的参数作为计数器，如果你想等待N个线程或者说等待N个执行步骤，那么可以将N作为参数传入。当我们调用一次CountDownLatch的countDown方法时，N就会减1，CountDownLatch的await会阻塞当前线程直到N为0。用于多个线程时，你只需要将这个CountDownLatch的引用传递到线程里。

public class CountDownLatchTest {

	static class Worker implements Runnable {
		private final CountDownLatch doneSignal;
		private final int i;

		public Worker(CountDownLatch doneSignal, int i) {
			this.doneSignal = doneSignal;
			this.i = i;
		}

		@Override
		public void run() {
			System.out.println("now is " + i);
			doneSignal.countDown();
		}

	}

	public static void main(String[] args) throws InterruptedException {
		int N = 10;
		CountDownLatch countDownLatch = new CountDownLatch(N);
		ExecutorService executor = Executors.newFixedThreadPool(N);
		for (int i = 0; i < N; i++)
			executor.execute(new Worker(countDownLatch, i));

		countDownLatch.await();
		System.out.println("over");
	}
}