BMT Transactions

[Dan T]

In spec of 17.6.1, it says:

If the client request is not associated with a transaction and the instance is already associated with a transaction T2, the container invokes the instance with the transaction that is associated with the instance (T2). This canse can never happen for a stateless Session Bean or a Message-drive Bean.

Does the following represent the scenerio above?

Client invokes on foo,

foo {
bar()
....
}


bar {
ut.begin()
.....
ut.commit()
}

I dont think it is right. What does transaction associated with instance mean?
Any why only for SB/MDB only?

Thanks.

[Valentin Crettaz]

This case can never happen with stateless session beans (SLSB) and message-driven beans (MDB) because the specification requires those beans to complete any started transaction at the latest when the method invocation returns. Since SLSB and MDB do not maintain any client-specific state, we have no guarantee that the same bean instance will serve two subsequent invocations from the same client. For this reason, transactions cannot span multiple method calls, and it is thus impossible for them to have ongoing transactions (T2) when they receive a new client request. Does this make sense?

[Dan T]

Thank you Valentin.
I understand what you said in the last post, but im still unclear about the terminology.

Im unclear the difference between:
instance transaction
the transaction that the method runs in

Does the instance transaction mean whether the method we are about to run have a ut.begin() in it?

[Billy Tsai]

which does entity bean not support?
CMT or BMT

[Valentin Crettaz]

Does the instance transaction mean whether the method we are about to run have a ut.begin() in it?
Not necessarly... If the bean uses bean-managed transaction demarcation, then yes. But if the bean uses container-managed transaction demarcation, the transaction will be started transparently by the container whenever some method is invoked (as specified in the deployment descriptor).

which does entity bean not support? CMT or BMT
Entity beans MUST NOT use BMT.