On 01/15/2015 09:16 PM, artnaseef wrote:
How about the following instead? As Tim pointed out, the consumer close
won't return until no more calls to onMessage are guaranteed. I believe
that also means it won't return while onMessage() is actively being called.
@Tim - can you confirm?
It should be the case that onMessage must always complete prior to
close() returning, unless you do something silly like call close from
onMessage. There are two locks at play here that prevent things from
going wrong, one on the listener and one on the dispatch queue. This is
why it is also safe to just call setMessageListener(null) on the
consumer as it will also not return until no onMessage calls are in
progress. During the time there is no set message listener the messages
will pile up in the prefetch queue and dispatch would start again once a
new listener is added.
If that's correct, the following should do the job effectively:
ON MESSAGE
LOCK semaphore
IF shutdown started
THEN
ABORT
END IF
SET processing active
UNLOCK semaphore
DO process message
LOCK semaphore
SET processing NOT active
UNLOCK semaphore
ON LISTENER SHUTDOWN
LOCK semaphore
SET shutdown started
UNLOCK semaphore
DO close consumer
SET not done
WHILE not done
LOCK semaphore
IF processing NOT active
THEN
SET done
END IF
UNLOCK semaphore
IF NOT done
THEN
DELAY // short sleep; note there are methods to eliminate the sleep
and use a notification; I don't recall them for C++ right now
END IF
END WHILE
DO delete message listener
That last part about the delay can be solved with another semaphore as well.
Also, if the part up to "ABORT" in the listener can be done safely even
after the listener is deleted, then this works even if the consumer close
can return while the call to onMessage() is still active.
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Tim Bish
Sr Software Engineer | RedHat Inc.
tim.b...@redhat.com | www.redhat.com
skype: tabish121 | twitter: @tabish121
blog: http://timbish.blogspot.com/
