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From "Emmanuel Lecharny (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DIRMINA-738) Using IoEventQueueThrottler with a WriteRequestFilter can lead to hangs
Date Tue, 06 Nov 2012 03:52:14 GMT

    [ https://issues.apache.org/jira/browse/DIRMINA-738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13491191#comment-13491191

Emmanuel Lecharny commented on DIRMINA-738:

I'm looking at the IoEventQueueThrottle class, and there is something embarrassing about it
: the polled() and offered() method are incrementing and decrementing the counter using an
unreliable method : estimateSize().

The estimateSize() method tries to compute the size of the message using reflection, but there
is no guarantee whatsoever that the computed size reflects the actual message size. This seems
a very brittle implementation, assuming that we could block the whole system if the threshold
is reached.

The problem is that the IoEventQueueThrottle is always used after the codec filter (there
is no way we can efficiently use an Executor filter before the codec filter : we might not
be able to correctly decode messages otherwise if the PDU is fragmented) so we never work
on a IoBuffer...

What you propose (ie matching the polled estimated size with the polled estimated size seems
a better approach : at least, the size would be equals...

I also do think that the notify() call could be replaced by a notifyAll() call, giving some
room for more than a thread to be processed if a big chunk of memory has been released, when
a call to notify() will only allow one single thread to proceed.

I can apply the suggested modifications, but I don't have a test to reproduce the environment...
> Using IoEventQueueThrottler  with a WriteRequestFilter can lead to hangs
> ------------------------------------------------------------------------
>                 Key: DIRMINA-738
>                 URL: https://issues.apache.org/jira/browse/DIRMINA-738
>             Project: MINA
>          Issue Type: Bug
>          Components: Filter
>    Affects Versions: 2.0.0-M6
>            Reporter: Daniel John Debrunner
> The javadoc for WriteRequestFilter  shows an example using IoEventQueueThrottler  to
throttle writes. First issue is that IoEventQueueThrottler  is not well documented, I'd assumed
it was throttling number of messages, instead its threshold is number of bytes. Second issue
is that if a message estimated length is less than the threshold then the write hangs, even
with an async executor in the chain.
> Emmanuel L├ęcharny  also wrote:
>   FYI, the counter (threshold) is *never* decreased.
> To be frank, this is not a piece of code I know, but from what I see, it's *extremely*
dubious that it does something useful, and most likely to block forever.
> I would suggest not to use this

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