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From "Joshua Smith" <j...@rationalpi.com>
Subject JMS Threading Restriction
Date Sat, 14 Jun 2008 00:50:32 GMT
All-

I'm reading a number of references on JMS written some time between 2001 and
now. The challenge that comes with that is knowing which things are still
true today and which things were describing the state of affairs at that
time. I found the following paragraph in the O'reilly Java Message Service
(First Edition) book written in 2001 on p. 32. Can anyone confirm that this
is still an accurate description of JMS?


"The Chat application ((which is what they use for their JMS example in the
book)) uses a separate session for the publisher and subscriber, pubSession
and subSession, respectively. This is due to a threading restriction imposed
by JMS. ***According to the JMS specification, a session may not be operated
on my more than one thread at a time.*** In our example, two threads of
control are active: the default main thread of the Chat application and the
thread that invokes the onMessage() handler. The thread that invokes the
onMessage() handler is owned by the JMS provider. Since the invocation of
the onMessage() handler is asynchronous, it could be called while the main
thread is publishing a message in the writeMessage() method. If both the
publisher and subscriber had been created by the same session, the two
threads could operate on these methods at the same time; in effect, they
could operate on the same TopicSession - a condition that is prohibited."
(emphasis mine)


Thanks,
Joshua Smith

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