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https://issues.apache.org/jira/browse/AMQ-4196?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13509315#comment-13509315
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Christian Posta commented on AMQ-4196:
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Art,
for (b), remove consumer (for a temp) and remove destination (for a temp) can
only come from one place (the connection it originated from), ie, another
connection cannot remove the temp or the consumer to the temp. When that
connection makes a call to remove the consumer for the temp, the thread that
handles it for that connection handles the remove in the broker and sends to
the advisory topic as well as sends to the subscription for the advisory topic.
Topics don't have a separate "dispatch thread" like queues do, so the ordering
for this case cannot race. The same thread that handled the connection is also
used in the TopicSubscription. If there were two separate connections involved
with sending the remove info and remove destination, then there could be a
race.
The only other thread involved is the thread for the consumer's connection.
When a topic sub dispatches to the consumer's connection it will do this by
default async. So it will be put into a "worker queue" for the connection
thread to finally send it over the wire. but the messages are put there by the
same thread and in order for this async dispatch.
If i've mispoken, I'm open to corrections :)
> Race condition between removal of subscriptions and removal of destinations
> in a network of brokers
> ---------------------------------------------------------------------------------------------------
>
> Key: AMQ-4196
> URL: https://issues.apache.org/jira/browse/AMQ-4196
> Project: ActiveMQ
> Issue Type: Bug
> Components: Broker, Connector
> Affects Versions: 5.6.0, 5.7.0
> Reporter: Gary Tully
> Assignee: Gary Tully
> Labels: Temp, networkBridge
> Fix For: 5.8.0
>
>
> n a broker network like this: A <--> B <---> C
> Scenario:
> A producer to BrokerA creates a message, sets its replyTo header to a temp
> destination that it creates and listens on, then sends the message off to
> broker A. The message is demand forwarded to BrokerC because there is a
> consumer there that consumes the message and replies to the temp dest in the
> replyTo header.
> As the number of concurrent producers on BrokerA sending these messages
> increases, the subscription to the temp destination that was demand forwarded
> will not be cleaned up properly on BrokerC. The reason for this is the
> DemandForwardingBridge runs the remove consumer code in a separate thread.
> But if a "remove destination" advisory messages comes in, it will remove the
> destination from the AdvisoryBroker's destination map. So if this happens
> before the code for removeConsumer runs (in AdvisoryBroker), then the
> destination will not be in the destination map and the advisory for
> removeConsumer will not fire.
> The net result is a subscription leak in the network bridge on B & C
> The junit test shows two issues:
> 1) the subscriptions leaked when concurrent producers using request/reply and
> correctly closing the consumer and connection
> 2) all subscriptions leaked when using a single producer with request/reply
> and closing only the connection, and not the consumer explicitly
> Issue 2 is related to temp destinations only and is compounded by
> https://issues.apache.org/jira/browse/AMQ-3879
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