并发编程：线程同步结束的两种方法-优快云博客

本文探讨了并发编程中线程同步结束的两种实现方式：使用Callable接口和Future集合，以及通过CountDownLatch或CyclicBarrier来协调线程执行顺序。详细解释了每个方法的工作原理及代码实现。

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随手记两个线程同步结束的例子

1.用Callable<V>

public class CallableThread implements Callable<Integer> {
	@Override
	public Integer call() throws Exception {
		DateTime dt1 = DateTime.now();
		String name = Thread.currentThread().getName();
		System.out.println(name + " start on " + dt1) ;
		Thread.sleep(new Random().nextInt(10) * 1000);
		DateTime dt2 = DateTime.now();
		Integer cost =  (int) ((dt2.getMillis() - dt1.getMillis()) / 1000);
		System.out.println(name + " end on " + dt2 + " cost time : "  + cost);
		return cost;
	}


	public static void main(String[] args) {
		List<Future<Integer>> count = Lists.newArrayList();
		ExecutorCompletionService<Integer> service = new ExecutorCompletionService<Integer>(Executors.newFixedThreadPool(5));  
		for(int i=0; i< 5; i++) {
			count.add(service.submit(new CallableThread()));
		}
		Integer total = 0;
		try {
			for(int i=0; i<count.size(); i++) {
				Future<Integer> f;
				f = service.take();
				total += f.get();
			}
		} catch (InterruptedException | ExecutionException e) {
			e.printStackTrace();
		}
		System.out.println("total cost:" + total + " aver cost " + total/count.size());
	}
}

2.用CountDownLatch（CyclicBarrier也可以达成一样的效果，写法大同小异）

public class CountDownLatchDemo implements Runnable {
	CountDownLatch latch;
	static final Map<String,Long> count = Maps.newConcurrentMap();
	ThreadDemo(CountDownLatch latch ){
		this.latch = latch;
	}

	public void run() {
		DateTime dt1 = DateTime.now();
		String name = Thread.currentThread().getName();
		System.out.println(name + " start on " + dt1);
		try {
			Thread.sleep(new Random().nextInt(10) * 1000);
		} catch (InterruptedException e1) {
			e1.printStackTrace();
		}

		DateTime dt2 = DateTime.now();
		Long cost = dt2.getMillis() - dt1.getMillis();
		System.out.println(name + " end on " + dt2 + " cost time : "  + cost);
		count.put(name, cost);
		latch.countDown();
	}

	public static void main(String args[]) throws Exception {
		CountDownLatch latch = new CountDownLatch(5);
		ExecutorService service = Executors.newFixedThreadPool(5);  
		for (int i = 0; i < 5; i++) {
			service.execute(new ThreadDemo(latch));
		}
		latch.await();
		Long total = 0L;
		System.out.println(count);
		for(Map.Entry<String, Long> s: count.entrySet()){
			total += s.getValue();
		}
		System.out.println("all threads ended, " + " average cost is " + total
				/ count.size());
	}
}