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From "bob.deremer" <bob.dere...@burningskysoftware.com>
Subject Re: Is it possible to have 1 MessageListener POJO handle multiple queues?
Date Thu, 04 Feb 2010 17:34:27 GMT

While this is possible, it's not desirable because of the dynamic nature of
my pub/sub.  I was planning to use the VirtualTopic [queue-backed] approach
for the dynamic event subscribing side of things because of the performance
it claims and the fact that each consumer/destination pair is run on it's
own thread from ActiveMQ's threadpool.  

So, for example, if I have P1 and P2 as the event publishers and C1 as the
subscriber [to both publisher's events], I would have the following
destinations:

P1 = VirtualTopic.P1
P2 = VirtualTopic.P2
C1 = Consumer.C1.VirtualTopic.P1
C1 = Consumer.C1.VirtualTopic.P2

As you can see from the VirtualTopic approach - the number of destinations
is really dynamic.  As C1 subscribes/unsubscribes to P# publishers - the
consumer/destination(s) will change.  I want to avoid having to do thread
management for all of this - since it appears that ActiveMQ should fit the
bill.

I'm working on the implementation now where I keep a
ConcurrentHashMap<String, MessageConsumer> collection.  When a new
subscription is added, I just create the consumer on the fly and wire it to
my existing OnMessage handler.  I'll see how this works.  It VirtualTopics
aren't designed for scenarios where there will be lots of subscribers and
the list changes dynamically at runtime - please let me know. 

Thanks,
Bob


Joe Fernandez wrote:
> 
> Can you have two instances of the same POJO? If so, create two separate
> threads with their own sessions to the appropriate destination and give
> each thread an instance of the POJO. 
> 
> What about spawning multiple threads, each having their own Session,
> instance of the message listener POJO, and pointed to a particular
> destination? 
> 
> Joe
> http://www.ttmsolutions.com
> 
> 
> bob.deremer wrote:
>> 
>> Hi ActiveMQ experts,
>> 
>> I have a scenario where I'd like to create a single MessageListener POJO,
>> but it needs to be a listener on multiple queues.  The reason is that I'm
>> trying to support the following 2 cases:
>> 
>> 1) a pub/sub event model using Virtual Topics.  As a result, each
>> subscriber (i.e. MessageListener) must be a separate Queue following the
>> VirtualTopic naming convention.  This means that there could be 0 - many
>> queues this single POJO may be receiving messages from - based on what
>> events the POJO is subscribed.  In addition, these subscriber queues will
>> be added/removed dynamically
>> 2) a request/reply model with the same POJO.  This one is easy, as I'll
>> create a single Queue/POJO to handle incoming request messages.
>> 
>> So, is this possible?  And - even if it's possible, [IS IT A GOOD IDEA?] 
>> While something may be possible, it might not be a design.  I cannot
>> create a single POJO per destination and to support both request/response
>> + event subscription - i will still need a minimum of 1 Topic + 1 Queue =
>> 2 destinations going to the same POJO.
>> 
>> Thanks in advance for any suggestions and please let me know if you need
>> any further details,
>> Bob DeRemer
>> 
> 
> 

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