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From "Arthur Naseef (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AMQ-4196) Race condition between removal of subscriptions and removal of destinations in a network of brokers
Date Mon, 10 Dec 2012 18:49:21 GMT

    [ https://issues.apache.org/jira/browse/AMQ-4196?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13528165#comment-13528165
] 

Arthur Naseef commented on AMQ-4196:
------------------------------------

I ran tests with a broker filter designed to detect out-of-order operations on temporary destinations.
 It ran into a problem in which one broker in the network saw a "DELETE DESTINATION" first
rather than the "CREATE DESTINATION".

Digging into that problem resulted in finding a problem resolved as a part of the changes
in AMQ-3253 (copying the DestinationInfo before sending in an advisory).

After applying that fix, I'm not seeing out-of-order operations, with the exception of occassional
"destination ... does not exist" errors when using a temporary destination as the JMSReplyTo
address due to a race between the request message and the temp advisories.

Note that this thread has been very illuminating.  PFC doesn't really handle all of the cases
I thought it would handle, and that needs careful consideration.

Lists of "what does ActiveMQ guarantee" (with a broker network and without), and "what ActiveMQ
does not guarantee" would be extremely useful.
                
> 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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