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From Donald Whytock <>
Subject Re: Cannot reply to a message routed by camel
Date Mon, 08 Nov 2010 04:02:44 GMT
Why not give each user its own SEDA queue and have the listener on the
main queue route messages among the user queues?  Each user would
still be single-threaded, but at least the listener wouldn't be
blocked and resubmits and delays wouldn't be necessary.


On Sun, Nov 7, 2010 at 8:00 PM, Krystian <> wrote:
> Hi,
> I know the way I am doing it might be a bit off from what is considered
> normal, however I couldn't do it any other way.
> I have a queue of user actions to be executed on the system.
> There are several concurrent listeners listening for the actions, and they
> take them off the queue and 'execute' them.
> If an action is executed for a user and another comes in for the same user
> it cannot be executed and has to wait for the first one to be completed.
> I would normally use ActiveMQ redelivery policy and have it done in a sec,
> however with redelivery policy delay the listener is blocked. I cannot have
> that. When one action is waiting same listener can execute few other actions
> and just increasing the number of concurrent listeners is not the way to go
> for me.
> To add some complexity to the process, after the action is finished I am
> sending a response back to thread which created the first message. I am
> using Spring and MessageListenerAdapter so it's pretty straight forward to
> do it.
> Now. In order to get around the delay I decided to use Camel delay pattern.
> I execute my custom bean to calculate the delay and thanks to the fact that
> all messages are delayed by the same amount of time messages are always
> delayed the way I want. To achieve that I had to resign from redelivery
> handling in ActiveMQ and I have it set to maximumRedeliveries = - and
> initialRedeliveryDelay = 0. Camel listens on ActiveMQ.DLQ queue and resends
> the messages to the original queue.
> Here's how it works:
> Start -> message sent to ActionQueue -> check if action can be executed:
> Yes -> action is executed -> response sent back      <- this works fine
> No -> transaction is rolled back -> ActiveMQ redelivery kicks in and sends
> message to ActiveMQ.DLQ -> camel picks up the message -> message delayed ->
> message sent to ActionQueue
> Unfortunately, after the message is sent to ActionQueue and is picked up by
> the listener, the response to this message never reaches the caller.
> I ran my app with debug logging and can see that when message is rerouted
> the reply-to queue changes.
> Is there any way I could get this to work?
> Thanks,
> Krystian
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