[hibernate-dev] JTA synchronizations on WildFly

[Scott Marlow]

Hi Gunnar,

Yes, this behaviour is expected since you registered an non-interposed 
synchronization.  For what purpose are you registering the transaction 
synchronization?  I would like to be aware of the synchronizations that 
we register in WildFly.

The non-interposed sync beforeCompletion callback are invoked first, 
then the interposed sync beforeCompletion calls, then the interposed 
afterCompletion(int status) calls and finally, the non-interposed 
afterCompletion(int status) calls.

The Synchronizations that are registered via the 
javax.transaction.TransactionSynchronizationRegistry.registerInterposedSynchronization(Synchronization) 
[2] are interposed.

Synchronizations that are registered via the 
javax.transaction.Transaction.registerSynchronization(Synchronization) 
[3] are non-interposed.

In WildFly, the transaction manager uses the registration order within 
the interposed/non-interposed group.  Before completion syncs (within 
their respective group), are run in registration order.  After 
completion syncs (within their respective group), are run in reverse 
registration order.

I believe that your workaround, mentioned below, of using 
JtaPlatform#registerSynchronization() on WildFly, is registering your 
synchronization as interposed via the TransactionSynchronizationRegistry 
[2]. There might be a way to register a sync callback at the Hibernate 
session level (which would also run as interposed sync on WildFly).

Not sure if you saw my email yesterday to Hibernate-dev ml.  You should 
be aware that the afterCompletion(int status) callback, may be called 
from a non-application thread when the WildFly tm reaper handles tx 
timeout (this can happen while the application thread is still invoking 
calls on the Hibernate session).  Because the Hibernate session is not 
thread safe, we need to ensure that the Hibernate session 
afterCompletion(int status) callback does not mutate the Hibernate 
session (e.g. calling session.clear() what status == rolled back).

Scott

[2] 
http://docs.oracle.com/javaee/5/api/javax/transaction/TransactionSynchronizationRegistry.html#registerInterposedSynchronization%28javax.transaction.Synchronization%29

[3] 
http://docs.oracle.com/javaee/5/api/javax/transaction/Transaction.html#registerSynchronization%28javax.transaction.Synchronization%29

On 03/10/2015 09:03 AM, Gunnar Morling wrote:
> Hi,
>
> I'm trying to perform a specific action upon transaction rollback.
>
> Assuming this could be done using a custom
> javax.transaction.Synchronization, I tried to register a synchronization as
> follows:
>
>      TransactionImplementor transaction = ...; // e.g. a CMTTransaction
>      transaction.registerSynchronization( new MySync() );
>
> And indeed beforeCompletion() is invoked as expected. But afterCompletion()
> never is. I debugged this a bit on WildFly and observed the following:
>
> * Hibernate ORM registers RegisteredSynchronization with JTA.
> RegisteredSynchronization manages (indirectly, through
> TransactionCoordinator, SynchronizationRegistry etc.) those
> synchronizations added through o.h.t.Transaction.registerSynchronization()
> * WildFly (specifically, TransactionUtil [1]) registers its own
> SessionSynchronization
> for closing the entity manager/session
>
> Now that second synchronization is called first, closing the session. Upon
> SessionImpl#close(), the SynchronizationRegistry is cleared. Then when
> afterComplection() is called on RegisteredSynchronization afterwards, any
> previously registered delegate synchronizations are gone already and thus
> do not get invoked.
>
> I believe I found a workaround for my case by registering my
> synchronization through JtaPlatform#registerSynchronization() (which
> registers it with the actual JTA transaction).
>
> My questions are:
>
> * Is this behaviour expected?
> * Is the work-around of doing the registration via JtaPlatform viable or
> are there any drawbacks which I'm not aware of?
>
> Thanks,
>
> --Gunnar
>
> [1]
> https://github.com/wildfly/wildfly/blob/master/jpa/src/main/java/org/jboss/as/jpa/transaction/TransactionUtil.java
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