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Re: To BlockingQueue or not to BlockingQueue?

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On 11/14/2015 5:24 PM, Eric Sosman wrote:
> On 11/13/2015 9:40 PM, Arne Vajhøj wrote:
>> public class ErSoQueueDQImpl implements ErSoQueue {
>>      private static class Token {
>>      }
>>      private static class InterruptedResult extends Result {
>>          public InterruptedResult() {
>>              super(false);
>>          }
>>      }
>>      private static class ErSoExceptionNothing extends ErSoException {
>>          private static final long serialVersionUID = 1L;
>>          public ErSoExceptionNothing() {
>>              super("Nothing to wait for");
>>          }
>>      }
>>      private ExecutorService es;
>>      private BlockingQueue<Result> results;
>>      private ConcurrentLinkedQueue<Token> tokens;
>>      public ErSoQueueDQImpl(int noworkers, int maxpending) {
>>          es = Executors.newFixedThreadPool(noworkers);
>>          results = new LinkedBlockingQueue<Result>(maxpending);
>>          tokens = new ConcurrentLinkedQueue<Token>();
>>      }
>>      @Override
>>      public void submitWork(final Work w) {
>>          tokens.add(new Token());
>>          es.submit(new Runnable() {
>>              @Override
>>              public void run() {
>>                  try {
>>                      results.put(w.call());
>>                  } catch (InterruptedException e) {
>>                      // this is expected in case of stop(false)
>>                      results.add(new InterruptedResult());
>>                  } catch (Exception e) {
>>                      // not specified what action should be done here
>>                      e.printStackTrace();
>>                  }
>>              }
>>          });
>>      }
>>      @Override
>>      public Result getResult() throws ErSoException {
>>          try {
>>              if(tokens.poll() != null) {
>>                  return results.take();
>>              } else {
>>                  throw new ErSoExceptionNothing();
>>              }
>>          } catch (InterruptedException e) {
>>              throw new ErSoException(e);
>>          }
>>      }
>>      @Override
>>      public void stop(boolean wait) {
>>          if(wait) {
>>              es.shutdown();
>>          } else {
>>              for(@SuppressWarnings("unused") Runnable r :
>> es.shutdownNow()) {
>>                  results.add(new InterruptedResult());
>>              }
>>          }
>>      }
>> }
>
>      Thank you, Arne.  I may have misunderstood your sketch, but
> something seems amiss inside the Runnable in submitWork().  If
> results.put() throws InterruptedException while waiting for the
> results queue to become non-full, the following results.add() probably
> won't have any better luck and will throw IllegalStateException.

Oops. That should be a blocking put.

I am assuming that it is a requirement to identify not completed tasks.

> That's all right from the perspective of the submitWork() caller,
> but look: The results queue is now out of step with the tokens queue.
> I don't think this can be fixed by plucking the extra token out of
> its queue again in the catch block, because some other thread may
> already have removed it with a call to getResult() ...

There were submitted a token back when the task was submitted.

Due to interrupt the real response will not show up, so
we send am interrupted result.

But there should still be a 1:1 correlation between tokens
and responses.

Unless I have missed something. Which could obvious be
the case.

>      By the way, couldn't the queue of Tokens just be a Semaphore?

Probably yes.

Arne

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Thread

To BlockingQueue or not to BlockingQueue? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-13 09:13 -0500
  Re: To BlockingQueue or not to BlockingQueue? Eric Douglas <e.d.programmer@gmail.com> - 2015-11-13 07:29 -0800
    Re: To BlockingQueue or not to BlockingQueue? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-13 10:41 -0500
      Re: To BlockingQueue or not to BlockingQueue? Eric Douglas <e.d.programmer@gmail.com> - 2015-11-13 07:57 -0800
  Re: To BlockingQueue or not to BlockingQueue? Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2015-11-13 16:56 -0800
    Re: To BlockingQueue or not to BlockingQueue? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-14 17:08 -0500
  Re: To BlockingQueue or not to BlockingQueue? Arne Vajhøj <arne@vajhoej.dk> - 2015-11-13 21:40 -0500
    Re: To BlockingQueue or not to BlockingQueue? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-14 17:24 -0500
      Re: To BlockingQueue or not to BlockingQueue? Arne Vajhøj <arne@vajhoej.dk> - 2015-11-14 19:13 -0500
  Re: To BlockingQueue or not to BlockingQueue? Steven Simpson <ss@my.domain.invalid> - 2015-11-15 10:37 +0000
  Re: To BlockingQueue or not to BlockingQueue? Sebastian <news@seyweiler.dyndns.org> - 2015-11-16 01:00 +0100

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