主线程等待所有子线程执行完成-优快云博客

本文通过两个示例演示了如何使用CountDownLatch来同步多个线程。第一个示例使用join方法等待每个子线程完成；第二个示例则利用CountDownLatch，使得主线程能够等待所有子线程执行完毕后再继续执行。

使用CountDownLatch使主线程等待所有子线程执行完，再继续执行。

	public static void main(String[] args) throws InterruptedException {
		t1();
		t2();
	}

	private static long getTime() {
		return System.currentTimeMillis();
	}

	public static void t3() {
		long dd1 = System.currentTimeMillis();
		while (getTime() - dd1 <= 100) {

		}
	}

	public static void t2() throws InterruptedException {
		long d1 = System.currentTimeMillis();
		int threadNumber = 10;
		final CountDownLatch countDownLatch = new CountDownLatch(threadNumber);
		for (int i = 0; i < threadNumber; i++) {
			final int threadID = i;
			new Thread() {
				public void run() {
					System.out.println("start" + threadID);
					t3();
					System.out.println("end" + threadID);
					System.out.println(String.format(
							"threadID:[%s] finished!!", threadID));
					countDownLatch.countDown();//该方法必须在run()方法中执行才起作用
				}
			}.start();
		}
		countDownLatch.await();
		System.out.println("main thread finished!!");
		long d2 = System.currentTimeMillis();
		System.out.println("time2:" + (d2 - d1));
	}

	public static void t1() throws InterruptedException {
		long d1 = System.currentTimeMillis();
		int threadNumber = 10;
		for (int i = 0; i < threadNumber; i++) {
			final int threadID = i;
			Thread thread = new Thread() {
				public void run() {
					System.out.println("start" + threadID);
					t3();
					System.out.println("end" + threadID);
					System.out.println(String.format(
							"threadID:[%s] finished!!", threadID));
				}
			};
			thread.start();
			thread.join();//等待该线程执行结束
		}
		System.out.println("main thread finished!!");
		long d2 = System.currentTimeMillis();
		System.out.println("time1:" + (d2 - d1));
	}