ExecutorService，避免任务队列太满的标准方法

我在用ExecutorService为了方便并发多线程程序。采取以下代码：

while(xxx) {
    ExecutorService exService = Executors.newFixedThreadPool(NUMBER_THREADS);
    ...  
    Future<..> ... = exService.submit(..);
    ...
}

就我而言，问题是submit()如果全部都没有阻塞NUMBER_THREADS被占用。结果是任务队列被许多任务淹没。这样做的结果是，关闭执行服务ExecutorService.shutdown()需要很长时间（ExecutorService.isTerminated()长时间内将是错误的）。原因是任务队列仍然很满。

现在我的解决方法是使用信号量来禁止任务队列中有太多条目ExecutorService:

...
Semaphore semaphore=new Semaphore(NUMBER_THREADS);

while(xxx) {
    ExecutorService exService = Executors.newFixedThreadPool(NUMBER_THREADS); 
    ...
    semaphore.aquire();  
    // internally the task calls a finish callback, which invokes semaphore.release()
    // -> now another task is added to queue
    Future<..> ... = exService.submit(..); 
    ...
}

我确信有更好的封装解决方案吗？

诀窍是使用固定的队列大小并且：

new ThreadPoolExecutor.CallerRunsPolicy()

我还推荐使用番石榴监听执行服务 https://github.com/google/guava/wiki/ListenableFutureExplained。 这是消费者/生产者队列的示例。

private ListeningExecutorService producerExecutorService = MoreExecutors.listeningDecorator(newFixedThreadPoolWithQueueSize(5, 20));
private ListeningExecutorService consumerExecutorService = MoreExecutors.listeningDecorator(newFixedThreadPoolWithQueueSize(5, 20));

private static ExecutorService newFixedThreadPoolWithQueueSize(int nThreads, int queueSize) {
    return new ThreadPoolExecutor(nThreads, nThreads,
                                  5000L, TimeUnit.MILLISECONDS,
                                  new ArrayBlockingQueue<Runnable>(queueSize, true), new ThreadPoolExecutor.CallerRunsPolicy());
}

如果有更好的，您可能需要考虑像 RabbitMQ 或 ActiveMQ 这样的 MQ，因为它们具有 QoS 技术。