[jBoss-Dev] Threads, transactions and XAResources

[Carlos Pita]

Hi!     I have the foolowing question:       Supose I have, for example, 2 bean-managed persistence entity bean instances in a pool. A client create a new entity and one of them is used. While it is being created, the bean instance gets a data source and opens a connection. In some way (perhaps storing it in another bean) the entity saves the connection. Then the second bean instance in the pool is activated; before creating a new connection it checks to see if there is a saved connection (in the place where the other instance saved it). The connection is already there, so the second bean uses it. Supose then that both instances where used in different transactional contexts. When the first got the connection the corresponding XAResource was enlisted with the first transaction. When the second reused the connection it was already enlisted with the first transaction (I can't see a place where a hook to stop/start the XAResource could be). The JTA specification says:       "Different Java threads may be using the same connection resource to access the resource manager if the connection spans multiple method invocation [...] it's possible for different threads to be invoking the XAResource start and end methods [...] If the applcation server allows multiple threads to use a singe XAResource object and the associated connection to the resource manager, it is the responsability of the application server to ensure that there is only one transaction context asociated with the resource at any point of time"       The EJB specification says:       "Because this resource factories allow the Container to affect resource management, the connections acquired through the resource manager connection factory are called managed resources (these resource factories allow the Container to implement connection pooing and !!!automatic enlistment of the connection with a transaction!!!)."       From this I couldn't not conclude that providing a special factory is the only way for a Container to asociate a XAResource with a transaction. But it says almost that, doesn't it?. So:   1) The scenario I described above is wrong -I mean, something in it is not possible- (I'm new with EJB). 2) EJB does't support "multiple threads to use a singe XAResource" so I should avoid the scenario. 3) The scenario is possible and EJB implementations have more tricks than those resource factories to reasociate (stop/start) XAResource with transactions.       (I could be a little off-topic because the question doesn't directly refer to jBoss. Sorry if this is the case: don't answer me. Or answer me if jBoss supports multiple threads with... :) )   Thank you in advance, Carlos.