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Date: Sun, 18 Mar 2007 11:49:34 -0700 (PDT)
From: "Nathan Mittler (JIRA)" <jira@apache.org>
To: dev@activemq.apache.org
Subject: [jira] Commented: (AMQCPP-90) Openwire Session doesn't run its
 MessageListeners from a single thread
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    [ https://issues.apache.org/activemq/browse/AMQCPP-90?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_38881 ] 

Nathan Mittler commented on AMQCPP-90:
--------------------------------------

If I understand this correctly, you're trying to cause an exception from your MessageListener and have it propagate to your ExceptionListener handler.

It would seem that throwing exceptions would violate the observer pattern.  The ExceptionListener is for exceptions that occur on the connection, itself - not user-generated error conditions.  I would say that what it does now  (absorb the user exception) is the correct behavior.

To achieve the results you're looking for, it would seem that you could have a common exception handler that is shared by both your ExceptionListener and MessageListener objects.  

> Openwire Session doesn't run its MessageListeners from a single thread
> ----------------------------------------------------------------------
>
>                 Key: AMQCPP-90
>                 URL: https://issues.apache.org/activemq/browse/AMQCPP-90
>             Project: ActiveMQ C++ Client
>          Issue Type: Bug
>          Components: Openwire
>    Affects Versions: 2.0
>            Reporter: Albert Strasheim
>         Assigned To: Nathan Mittler
>             Fix For: 2.0
>
>         Attachments: MultipleConsumerTest.cpp, MultipleConsumerTest.java
>
>
> According to the JMS 1.1 specification, section 4.4.14 Serial Execution of Client Code:
> For this reason, JMS does not cause concurrent execution of client code unless
> a client explicitly requests it. One way this is done is to define that a session
> serializes all asynchronous delivery of messages.
> To receive messages asynchronously, a client registers an object that
> implements the JMS MessageListener interface with a MessageConsumer. In effect,
> a Session uses a single thread to run all its MessageListeners. While the thread is
> busy executing one listener, all other messages to be asynchronously delivered
> to the session must wait.
> In the attached code I have 5 consumers created from the same session, all with the same message listener instance that receives a message, prints something and then sleeps for a while. When running the C++ code, one sees that 5 messages (there are 5 consumers) are delivered at approximately the same time. Under Java, one only sees 1 message delivered per interval.
> This seems to indicate that the Openwire Session doesn't run its MessageListeners from a single thread. This can cause problems if the user's MessageListener isn't thread safe.

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