Transactions do not work properly with JMS producer endpoint when processing
InOut exchanges
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Key: CAMEL-2001
URL: https://issues.apache.org/activemq/browse/CAMEL-2001
Project: Apache Camel
Issue Type: Bug
Components: camel-jms
Affects Versions: 2.0.0
Reporter: Fintan Bolton
Fix For: Future
You cannot really use transactions with a JMS producer endpoint when processing
_InOut_ exchanges. Depending on the scenario, the route either hangs or the
implemented behavior is not very useful.
Here is a summary of the current (not very useful) behavior:
After experimenting with JMS transacted endpoints for a bit and looking at the
source, here is what I found the behavior to be for JMS producer endpoints:
# On the request leg (sending the JMS message), if there is no existing
transaction context, the producer will either create a transaction for sending
the message (if {{transactedInOut=true}} or not (if {{transactedInOut=false).
In any case, since the transaction only lasts as long as it takes to push the
message onto the outoing queue, it is not particularly interesting. Meaningful
transactions are generally used to bracket multiple (i.e. >1) updates of a
persistent resource.
# On the request leg, if there *is* an existing transaction context, the
producer joins the current transaction (irrespective of the value of
{{transactedInOut}}), provisionally writes the message to the outgoing queue,
and then starts waiting for the reply. In this case, the route hangs, because
the send is never committed.
# On the reply leg, the message is received in a separate thread. This step is
transactional, but the transaction ends as soon as the message has been pulled
off the queue, so it is also not very interesting.
Here is what I think would be useful behavior for a JMS producer endpoint:
# On the request leg, if there is an existing transaction context, the producer
joins the current transaction, provisionally writes the message to the outgoing
queue, and then *commits* the current transaction directly afterwards. This
prevents the route from hanging. *Note:* There is some code in the
{{CamelJmsTemplate}} class looks like it was intended to do this, but it
currently does not work. See child issue for more details.
# On the reply leg, create a new transaction in the main thread that includes
the action of pulling the reply off the incoming queue. This would require that
the reply be received in the main thread, not a sub-thread (as currently).
Subsequent nodes in the route could then participate in this transaction.
Admittedly, this would be a tricky feature to implement, because it would
involve making a big change to the producer's threading model.
I'm shortly going to add a couple of child JIRAs here to explain some related
issues.
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