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https://issues.apache.org/jira/browse/QPID-8538?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17360895#comment-17360895
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Robbie Gemmell edited comment on QPID-8538 at 6/10/21, 1:31 PM:
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Going back on my last-reply note, I will add a final note that I wouldn't
really consider the original behaviour to really be a bug from what I
understand of it so far. It may not do what you want, and it could behave
differently like most things usually can, but that doesnt mean it is a bug. Its
possible I may not have fully understood the issue given the various problems
with the description. I do see potential for problems stemming from some of the
changes you had suggested as I noted. If you are happy with your local changes
though then great, I leave you to it.
was (Author: gemmellr):
Going back on my last-reply note, I will add a final note that I wouldn't
really consider the original behaviour to really be a bug from what I
understand of it so far. It may not do what you want, and it could behave
differently like most things usually can, but that doesnt mean it is a bug. Its
possible may not have fully understood the issue given the various problems
with the description. I do see potential for problems stemming from some of the
changes you had suggested as I noted. If you are happy with your local changes
though then great, I leave you to it.
> Receiver fetch method depletes credit and slows down receiver
> -------------------------------------------------------------
>
> Key: QPID-8538
> URL: https://issues.apache.org/jira/browse/QPID-8538
> Project: Qpid
> Issue Type: Bug
> Components: C++ Client
> Affects Versions: qpid-cpp-1.39.0
> Reporter: Peter Moran
> Priority: Major
>
> As remote broker java broker is used.
> e.g
> capacity of link is 10
> credit is 10
> When calling Method ConnectionContext::fetch and there are no data available
> inside receiver (get returns false) it
> # Enables drain mode pn_link_drain(lnk->receiver, 0);
> # Tries to process all queued messages (while
> (pn_link_draining(lnk->receiver) && !pn_link_queued(lnk->receiver)))
> # Credit is being drained by broker pn_do_flow in proton ( pn_sequence_t
> delta = delivery_count - link->state.delivery_count;) -> delta is 10 and
> credit is cleared to 0, yet no messages arrived from broker at all
> if there are queued messages and credit is 0 then pn_link_draining returns
> false and while stops
> # however if (lnk->capacity && pn_link_queued(lnk->receiver) == 0) replenish
> credit only if there are no outstanding queued messages to the maximum
> capacity, this should be rather capacity - credit, but also the condition
> seems to be wrong, it should not check the queued messages.
> the code should look like this
> {code:java}
> if (lnk->capacity) {
> pn_link_flow(lnk->receiver, lnk->capacity -
> pn_link_credit(lnk->receiver));
> }
> or
> if (lnk->capacity) {
> pn_link_flow(lnk->receiver, pn_link_drained(lnk->receiver));
> }{code}
> this would much more look like what is inside proton c++ api
> {code:java}
> void credit_topup(pn_link_t *link) {
> assert(pn_link_is_receiver(link));
> int window = link_context::get(link).credit_window;
> if (window) {
> int delta = window - pn_link_credit(link);
> pn_link_flow(link, delta);
> }
> }
> // receiver
> if (!pn_link_credit(lnk) && lctx.draining) {
> lctx.draining = false;
> pn_link_set_drain(lnk, false);
> receiver r(make_wrapper<receiver>(lnk));
> handler.on_receiver_drain_finish(r);
> }
> credit_topup(lnk);
> {code}
> there is no condition about queued and also the resulting credit is set to
> the link capacity
> (e.g 10 - delta) delta is delivery count reduced from by pn_do_flow,
> However this to me looks like some incompatibility between client and broker,
> as one would not expect that delta is 10 if no messages are received from
> broker. is this some kind of message sequencing problem?
>
> fyi pn_link_queued messages does not mean they they are locally available
> they might be still on broker and also getAvaialable implementation is wrong.
>
>
>
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