ExecutorService.invokeAny()和ExecutorService.invokeAll()的使用剖析

/**
     * Executes the given tasks, returning the result
     * of one that has completed successfully (i.e., without throwing
     * an exception), if any do. Upon normal or exceptional return,
     * tasks that have not completed are cancelled.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     *
     * @param tasks the collection of tasks
     * @return the result returned by one of the tasks
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks or any of its elements
     *         are <tt>null</tt>
     * @throws IllegalArgumentException if tasks is empty
     * @throws ExecutionException if no task successfully completes
     * @throws RejectedExecutionException if tasks cannot be scheduled
     *         for execution
     */
    <T> T invokeAny(Collection<? extends Callable<T>> tasks)
        throws InterruptedException, ExecutionException;

public static void testInvokeAll() throws Exception
{
	ExecutorService executorService = Executors.newFixedThreadPool(5);

	List<Callable<String>> tasks = new ArrayList<Callable<String>>();
	tasks.add(new SleepSecondsCallable("t1", 2));
	tasks.add(new SleepSecondsCallable("t2", 2));
	tasks.add(new RandomTenCharsTask());
	tasks.add(new ExceptionCallable());

	// 调用该方法的线程会阻塞,直到tasks全部执行完成(正常完成/异常退出)
	List<Future<String>> results = executorService.invokeAll(tasks);

	// 任务列表中所有任务执行完毕,才能执行该语句
	System.out.println("wait for the result." + results.size());

	executorService.shutdown();

	for (Future<String> f : results)
	{
		// isCanceled=false,isDone=true
		System.out.println("isCanceled=" + f.isCancelled() + ",isDone="
				+ f.isDone());

		// ExceptionCallable任务会报ExecutionException
		System.out.println("task result=" + f.get());
	}
}

/**
 * 可以通过Future.isCanceled()判断任务是被取消,还是完成(正常/异常)<br>
 * Future.isDone()总是返回true,对于invokeAll()的调用者来说,没有啥用
 */
public static void testInvokeAllTimeout() throws Exception
{
	ExecutorService executorService = Executors.newFixedThreadPool(5);

	List<Callable<String>> tasks = new ArrayList<Callable<String>>();
	tasks.add(new SleepSecondsCallable("t1", 2));
	tasks.add(new SleepSecondsCallable("t2", 2));
	tasks.add(new SleepSecondsCallable("t3", 3));
	tasks.add(new RandomTenCharsTask());

	List<Future<String>> results = executorService.invokeAll(tasks, 1,
			TimeUnit.SECONDS);

	System.out.println("wait for the result." + results.size());

	for (Future<String> f : results)
	{
		System.out.println("isCanceled=" + f.isCancelled() + ",isDone="
				+ f.isDone());
	}

	executorService.shutdown();

}

执行结果是： 

wait for the result.4
 isCanceled=true,isDone=true
 isCanceled=true,isDone=true
 isCanceled=true,isDone=true
 isCanceled=false,isDone=true

/**
 * 如果线程在等待invokeAll()执行完成的时候,被中断,会抛出InterruptedException<br>
 * 此时线程池会终止没有完成的任务,这主要是为了减少资源的浪费.
 */
public static void testInvokeAllWhenInterrupt() throws Exception
{
	final ExecutorService executorService = Executors.newFixedThreadPool(5);

	// 调用invokeAll的线程
	Thread invokeAllThread = new Thread() {

		@Override
		public void run()
		{
			List<Callable<String>> tasks = new ArrayList<Callable<String>>();
			tasks.add(new SleepSecondsCallable("t1", 2));
			tasks.add(new SleepSecondsCallable("t2", 2));
			tasks.add(new RandomTenCharsTask());

			// 调用线程会阻塞,直到tasks全部执行完成(正常完成/异常退出)
			try
			{
				List<Future<String>> results = executorService
						.invokeAll(tasks);
				System.out.println("wait for the result." + results.size());
			} catch (InterruptedException e)
			{
				System.out
						.println("I was wait,but my thread was interrupted.");
				e.printStackTrace();
			}

		}
	};

	invokeAllThread.start();

	Thread.sleep(200);

	invokeAllThread.interrupt();

	executorService.shutdown();

}