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https://issues.apache.org/jira/browse/PROTON-200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13580630#comment-13580630
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Rafael H. Schloming commented on PROTON-200:
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I agree it's a release blocker to fix it in some form. There are actually a
number of areas of work involved in fixing this long-term. As mentioned above
there are two scenarios:
1) The messenger has handed out all of its credit and gets a new link. This is
in some ways easier to address as it simply requires re-balancing the credit,
but in order to do that the engine needs some updates to allow revoking of
credit. This is permitted by the protocol, but not currently fully supported by
the engine. I'm currently working on a patch for engine support.
2) The messenger has more links than it has credit to hand out. Once again
we're missing a little bit of engine support to fix this properly. The protocol
allows a peer with available messages to advertise that fact to its partner
(i.e. request credit) via the available field in the flow control frame, and
the partner can then use this information to allocate credit. There is already
a JIRA for the engine portion of this work (PROTON-39).
Beyond (1) and (2), another more straightforward measure we can take is to
provide an unlimited mode, e.g. in the bindings make the argument to
pn_messenger_recv optional, and for C define pn_messenger_recv(-1) to mean "no
specific limit". This would allow the internals to dynamically determine how
much credit to hand out and would make dealing with these problems relatively
simple, although it wouldn't allow the application to limit its exposure to
incoming messages. My guess is this is the quickest/most complete
fix/workaround for 0.4.
So to summarize I'd say there are probably n separate chunks of work here each
worthy of there own JIRA:
1) allow pn_messenger_recv(-1) to mean no specific limit
2) engine support for revoking of credit
3) engine support for advertising available messages (PROTON-39)
4) messenger support for re-allocating credit (removing from one peer and
giving to another)
> [Proton-c] Credit distribution by messenger is not balanced across all links
> ----------------------------------------------------------------------------
>
> Key: PROTON-200
> URL: https://issues.apache.org/jira/browse/PROTON-200
> Project: Qpid Proton
> Issue Type: Bug
> Components: proton-c
> Affects Versions: 0.3
> Reporter: Ken Giusti
> Assignee: Ken Giusti
> Fix For: 0.4
>
> Attachments: proton-200.patch
>
>
> The method used to distribute credit to receiving links may lead to
> starvation when the number of receiving links is > the available credit.
> The distribution algorithm always starts with the same link - see
> messenger.c::pn_messenger_flow()
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