topic Re: Sending BPMN signal upon variable update in Alfresco Archive

Sending BPMN signal upon variable update

franck102 — Wed, 27 May 2015 13:43:26 GMT

Hi all,We are trying to have implement a backend extension that will send out a BPMN signal (i.e. notify subscribers) whenever a given process variable is modified.The issue we are running into is that, the way we understand it, using an Activiti listener to fire the signal asynchronously means that

Re: Sending BPMN signal upon variable update

martin_grofcik — Thu, 28 May 2015 07:36:38 GMT

Hi Franck.

I have 2 ideas:

Regards
Martin

Re: Sending BPMN signal upon variable update

franck102 — Sat, 30 May 2015 06:21:19 GMT

Ouch, both options sound pretty scary.

Isn't there a way to programmatically create the equivalent of a BPMN continuation, something that isn't a TransactionListener but that would execute after the variable is committed, and would throw the signal? Maybe scheduling a job with the job manager?

Franck

Re: Sending BPMN signal upon variable update

trademak — Sun, 31 May 2015 12:59:07 GMT

Hi Franck,

Event listeners could be used for this. If you register an event listener on a variable create/update you get a trigger every time a variable is updated or created. There's an option to store al events in the Activiti database table ACT_EVT_LOG and you could create a thread that reads new rows from this event log table. When its written to this table you are sure that the transaction has been committed successfully.

Best regards,

Re: Sending BPMN signal upon variable update

martin_grofcik — Tue, 02 Jun 2015 07:05:51 GMT

Hi,
I think it does not solve

The issue we are running into is that, the way we understand it, using an Activiti listener to fire the signal asynchronously means that subscribers may start executing before the new variable value has been committed to the database.

Regards
Martin

Re: Sending BPMN signal upon variable update

franck102 — Wed, 04 Nov 2015 13:28:41 GMT

Indeed… the issue is still pending for us pm 5.15.1, if there is anything in the latest releases that would help with this I would love any pointers you can give.

Thanks!
Franck

Re: Sending BPMN signal upon variable update

jwestra — Thu, 28 Apr 2016 21:46:50 GMT

Franck,

If you are using Spring, you can implement a org.springframework.transaction.support.TransactionSynchronization listener that will be notified when a transaction is committed (e.g. it's afterCommit() method).

1. Store your modified variables in a resource holder attached to the Spring Transaction. If using Spring, Activiti DB commands will be using a Spring Transaction, so you are good to go.

2. In your implementation's 'afterCommit()' method, take the variable(s) and/or signal and fire them off IN A SEPARATE THREAD. The current thread just had a txn on it and it won't like you doing more work on it. So, spin off a separate thread for this signal.

Jason