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https://issues.apache.org/jira/browse/QPID-3079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13047244#comment-13047244
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[email protected] commented on QPID-3079:
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/branches/qpid-3079/qpid/cpp/src/qpid/broker/PersistableQueue.h
<https://reviews.apache.org/r/860/#comment1747>
Ok, discussed this with Kim - his understanding of this pointer is that it
is owned by the persistent queue, and the queue should be responsible for
calling delete on it. If that is the case, then there is a bug in that the
store is referencing this context after the queue is destroyed.
I will work with Kim on this to better understand the root cause and fix it
properly.
/branches/qpid-3079/qpid/cpp/src/qpid/broker/Queue.cpp
<https://reviews.apache.org/r/860/#comment1749>
"All you need to know is when they all complete" - not true: we need to
know when _each_ dequeue completes. This is not like the enqueue case - we
need to known when each dequeue is complete as the Message.Accept may be only
interested in that one particular dequeue event.
Which is what QPID-3079 is specifically trying to solve.
/branches/qpid-3079/qpid/cpp/src/qpid/broker/SemanticState.cpp
<https://reviews.apache.org/r/860/#comment1748>
Because of this: https://bugzilla.redhat.com/show_bug.cgi?id=698721
Store will not complete the dequeue for up to one second *if* it doesn't
have enough work to perform immediately.
Broker needs to force fast completion on Execution.Sync - it does this by
issuing a flush() on the command.
And that's why a simple counter won't work here - we need to track the
queues that are in the process of dequeuing specifically in case a flush is
called.
/branches/qpid-3079/qpid/cpp/src/qpid/broker/SemanticState.cpp
<https://reviews.apache.org/r/860/#comment1750>
Which is what I'm trying to do - at least at the SemanticState level (with
the message accept context). Its just that the message.accept context has to
be able to track N outstanding dequeues in order to know when it is complete
(could be a counter), or if the SessionState flushes the command (counter not
sufficient - it needs list of messages or queues to flush).
Let me step back a bit - there are three layers of abstraction introduced
by this patch:
1) SessionState/SessionContext needs to allow for async commands with an
abstract api (i.e. - SessionState doesn't care about the command specifics, it
just needs to know when it is complete, and be able to flush the command if
needed) See changes in SessionContext.
2) SemanticState uses one of these abstract "async command contexts" for
the Message.Accept command. This context must monitor a _set_ of outstanding
dequeues in order to 1) know when the command is complete, and 2) which
queues/messages need flushing should SessionState requires a flush.
3) The Queue needs to provide a callback when a particular message is
dequeued (not when all dequeues complete for a given message). The callback
needs to identify the queue and the particular message that has completed
dequeue.
#3 could be tracked by the message instead, but we still need to know when
-each- dequeue completes, so then the message would have to track each of its
concurrent dequeue's state (and target queue). I think that's exactly what
I've got Queue doing now anyways, and I think representing that in the Queue is
more "natural" - but that's more my artistic opinion :)
- Kenneth
On 2011-06-08 20:31:05, Kenneth Giusti wrote:
bq.
bq. -----------------------------------------------------------
bq. This is an automatically generated e-mail. To reply, visit:
bq. https://reviews.apache.org/r/860/
bq. -----------------------------------------------------------
bq.
bq. (Updated 2011-06-08 20:31:05)
bq.
bq.
bq. Review request for qpid, Alan Conway, Gordon Sim, and Kim van der Riet.
bq.
bq.
bq. Summary
bq. -------
bq.
bq. Modifies the broker's handling of Message.Accept to hold off the
completion of the command until all messages related to the accept have
completed dequeue. This particularly applies to persistent messages, as the
store::dequeue() operation must complete before the message is considered fully
dequeued.
bq.
bq. Note this bugfix requires some changes to the broker's store module
interface: previously, the store only identified the message when a dequeue
was completed. This is not enough information - the queue from which is was
removed must also be identified (the message may be in the process of being
dequeued on several queues at once).
bq.
bq.
bq. This addresses bug qpid-3079.
bq. https://issues.apache.org/jira/browse/qpid-3079
bq.
bq.
bq. Diffs
bq. -----
bq.
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/AsyncCompletion.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/DeliveryRecord.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/DeliveryRecord.cpp 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/Message.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/Message.cpp 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/MessageStore.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/MessageStoreModule.h
1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/MessageStoreModule.cpp
1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/NullMessageStore.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/NullMessageStore.cpp
1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/PersistableMessage.h
1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/PersistableMessage.cpp
1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/PersistableQueue.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/Queue.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/Queue.cpp 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/RecoverableQueue.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/RecoveryManagerImpl.cpp
1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/SemanticState.cpp 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/SessionContext.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/SessionState.h 1124895
bq. /branches/qpid-3079/qpid/cpp/src/qpid/broker/SessionState.cpp 1124895
bq. /branches/qpid-3079/qpid/cpp/src/tests/AsyncCompletion.cpp 1124895
bq. /branches/qpid-3079/qpid/cpp/src/tests/QueueTest.cpp 1124895
bq. /branches/qpid-3079/qpid/cpp/src/tests/TestMessageStore.h 1124895
bq.
bq. Diff: https://reviews.apache.org/r/860/diff
bq.
bq.
bq. Testing
bq. -------
bq.
bq. broker unit tests, store unit tests (modified jboss store). Still needs
to be vetted on non-linux, and have latest trunk merged in.
bq.
bq.
bq. Thanks,
bq.
bq. Kenneth
bq.
bq.
> message.accept command should be completed on a per-dequeue basis
> -----------------------------------------------------------------
>
> Key: QPID-3079
> URL: https://issues.apache.org/jira/browse/QPID-3079
> Project: Qpid
> Issue Type: Bug
> Components: C++ Broker
> Affects Versions: 0.8, 0.9
> Reporter: Ken Giusti
> Assignee: Ken Giusti
> Fix For: 0.11
>
> Attachments: proposal.txt
>
>
> ** Overview
> Asynchronous completion means that command execution is initiated in one
> thread
> (a client connection thread) and completed in a different thread.
> When the async store is loaded, message.transfer commands are
> completed by a store thread that does the async write.
> ** Issues with asynchronous completion code as of revision r1029686
> *** Not really asynchronous
> IncompleteMessageList::process blocks the connection thread till all
> outstanding async commands (messages) for the session are complete.
> With the new cluster, this could deadlock since it is blocking a Poller
> thread.
> *** Race condition for message.transfer
>
> Sketch of the current code:
> // Called in connection thread
> PersistableMessage::enqueueAsync { ++counter; }
> // Called in store thread once message is written.
> PersistableMessage::enqueueComplete { if (--counter == 0) notifyCompleted(); }
> The intent is that notify be called once per message, after the
> message has been written to each queue it was routed to.
> However of a message is routed to N queues, it's possible for
> notifyCompleted to be called up to N times. The store thread could
> call notifyCompleted for the first queue before the connection thread
> has called enqueueAsync for the second queue, and so on.
> *** No asynchronous completion for message.accept
> We do not currently delay completion of message.accept until the
> message is deleted from the async store. This could cause duplicate
> delivery if the broker crashes after completing the message but
> before it is removed from store.
> There is code in PersistableMessage to maintain a counter for dequeues
> analogous to to the async enqueue code but this is incorrect.
> Completion of transfer is triggered when all enqueues for a message are
> complete.
> Completion of accept is triggered for *each* dequeue from a queue
> independently.
> Furthermore a single accept can reference many messages, so it can't be
> associated with a message.
> ** New requirements
> The new cluster design will need to participate in async completion, e.g.
> an accept cannot be comlpeted until the message is
> - removed from store (if present) AND
> - replicated to the cluster (if present) as dequeued
> The new cluster also needs to asynchronously complete binding commands
> (declare, bind, delete) when they are replicated to the cluster.
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