QueueBrowser and unacked received messages

Greetings!
I was wondering if someone could explain or suggest a solution to the  
behavior I'm seeing?

using openjms-0.7.6.1, and a queue.
I'm trying to avoid having functionally equivalent jms messages on  
the queue at the same time.

I thought I could determine this by using a QueueBrowser and a  
message selector but apparently queued messages that are received but  
not ack'd (and take quite awhile to process) are skipped by the  
selector - at least they aren't returned in the browsers enumeration.

Is there a way to detect messages in this condition?
In my scenario the jms messages represent a request for a service and  
it doesn't make sense to have multiple copies of the same request on  
the queue at the same time.

Thanks.




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