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MQSeries.net Forum Index » IBM MQ Java / JMS » Multiple JMS clients prevent shared access to queue manager

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Multiple JMS clients prevent shared access to queue manager

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vennela

Posted: Sat Jun 26, 2004 3:47 pm Post subject:

Jedi Knight

Joined: 11 Aug 2002
Posts: 4055
Location: Hyderabad, India

From JustinM's original post:

Quote:

The problem that I am having is that when I start up more than a single client (in separate java vms)

from fjb_saper's last post

Quote:

I guess translating that into JMS, it means that each thread needs to use its own QueueConnection instance.

I don't think JustinM is using a single multi threaded app.

JustinM

Posted: Sun Jun 27, 2004 10:36 pm Post subject:

Novice

Joined: 10 Apr 2002
Posts: 13

Quote:

I don't think JustinM is using a single multi threaded app.

Correct - I could duplicate the problem using 2 single threaded clients in separate VMs.

A colleague of mine just passed on an article published by Sun (Enterprise Java Technologies Tech Tips for June 25, 2004) (http://enews.sun.com/CTServlet?id=62887183-1724121837:1088182019270) in which I found a peculiar statement:

Under the

Quote:

A Queue ensures that each message is delivered exactly once (or zero times, if it expires) to only one receiver. Only one receiver can connect to a Queue at any one time. The JMS provider (the server that implements the JMS interfaces) blocks attempts by receivers to connect to a busy Queue.

Now the first part of the statement makes sense to me (this is a fundamental of p-to-p messaging). The second statement is what caught my attention.
If only one receiver can connect to a queue at any one time, that would explain my problem. But (as many of us have seen) the POC(s) that we have run have enabled us to have multiple clients connecting to a single queue at the same time.

Now I'm not sure if I am taking this quote out of context or if IBM notion of a connection to a queue is different to a QueueConnection. what I mean is that they may have implemented the following:

- Connect to queue manager (QueueConnection)
- Create QueueReceiver

- Receive message (1)
- Acknowledge (2)

(repeat 1 and 2 multiple time)

- Disconnect from queue manager

IBM may interpret the statement above to mean that only a single receiver may receive a message at any one time (i.e. receives are synchronised between all receivers) but that multiple receivers may be 'listening' for messages at a given time. i.e

- Connect to queue manager (QueueConnection)
- Create QueueReceiver

- 'Connnect'
- Receive message (1)
- Acknowledge (2)
- 'Disconnect'

(repeat 1 and 2 multiple time)

- Disconnect from queue manager

I'm no closer to the explanation on this side and am only speculating. Unfortunately as I have mentioned previously I don't have access to either the machine that the queue manager is running on so can't go digging around in log files etc.

Justin

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