[hibernate-dev] JTA synchronizations on WildFly

[Emmanuel Bernard]

Scott, for Hibernate OGM and for non transactional datastores, we collect the list of executed operations and offer the list if the user calls Hibernate’s transaction.rollback() or if the JTA transaction is rollbacked. Note that the JTA transaction has no resource attached to it since the datastore is non transactional, we just piggyback on the begin / commit lifecycle without their true semantic.
This feature is called the ErrorHandling or Compensation API in OGM. That’s why we want to attach a Synchronization.

> On 10 Mar 2015, at 14:39, Scott Marlow <smarlow at redhat.com> wrote:
> 
> 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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