Interesting. What you've described Pedro is similar to what I'm trying to achieve, and also relates to some earlier posts I made to the list (title: 'Drools Flow: Problem with constraint in (Wait) State node').
I have a process that launches independent sub flows; these independent sub flows execute on separate threads. I then want the original process to "block" until all the subflows have finished, and to then continue.
In order to achieve this, I've done the following:

- Each process (both the main flow and each sub flow) is executed by a separate stateful knowledge session.
- When a sub flow is started, it inserts a fact into the working memory of the session for the original process.
- When a sub flow finishes, it updates a fact in the working memory of the session for the original process to "signal" its completion.
- After launching the sub flows, the original process contains a (wait) state node; the constraint for this node is designed to block until all facts in its memory are in the "signalled" state.

I've attached an example project that illustrates what I'm trying to achieve. The constraint on the wait state node is currently as follows:

(and forall(SimpleFact(complete == true)) exists(SimpleFact()))

I'd be interested to know from someone who understands rule syntax better than me as to why this seems to work when other attempts (see my earlier posts) failed.

I still have two problems though:

1) The above constraint appeared to work OK with an earlier 5.1 snapshot build (from a couple of months back). However, using the latest successful build from trunk (#3845), the Action node after the wait state node isn't executed. Given that 5.1.M2 is supposed to be imminent, I'm worried. Does anyone know why this no longer works?

2) If I try to enable JPA-based state persistence, using the Bitronix transaction manager, then when I try to insert a fact into the  working memory of the session for the original process from a separate thread, I get the following error:

bitronix.tm.internal.BitronixRollbackException: transaction was marked as rollback only and has been rolled back
        at bitronix.tm.BitronixTransaction.commit(BitronixTransaction.java:153)
        at bitronix.tm.BitronixTransactionManager.commit(BitronixTransactionManager.java:96)
        at org.drools.persistence.session.SingleSessionCommandService.execute(SingleSessionCommandService.java:258)
        at org.drools.command.impl.CommandBasedStatefulKnowledgeSession.insert(CommandBasedStatefulKnowledgeSession.java:306)
        at com.test.InsertWorkItemHandler$1.insertFact(InsertWorkItemHandler.java:52)
        at com.test.InsertWorkItemHandler$1.run(InsertWorkItemHandler.java:40)
        at java.lang.Thread.run(Thread.java:619)
java.lang.RuntimeException: Could not rollback transaction
        at org.drools.persistence.session.SingleSessionCommandService.execute(SingleSessionCommandService.java:283)
        at org.drools.command.impl.CommandBasedStatefulKnowledgeSession.insert(CommandBasedStatefulKnowledgeSession.java:306)
        at com.test.InsertWorkItemHandler$1.insertFact(InsertWorkItemHandler.java:52)
        at com.test.InsertWorkItemHandler$1.run(InsertWorkItemHandler.java:40)
        at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.IllegalStateException: no transaction started on this thread
        at bitronix.tm.BitronixTransactionManager.rollback(BitronixTransactionManager.java:103)
        at org.drools.persistence.session.SingleSessionCommandService.execute(SingleSessionCommandService.java:278)
        ... 4 more

Any help anyone can provide would be very much appreciated. Thank you.

Regards,

Alan




Pedro Maria Buitrago Mantilla <pmbtgun@gmail.com>
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23/04/2010 14:38
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Re: [rules-users] Multithreading work items





Each of the sub flows requires final user design. Mauricio thanks very much.

PEDRO BUITRAGO
Bogotá, Colombia
2010/4/22 Mauricio Salatino <salaboy@gmail.com>
yes.. sounds more like a normal java problem than Drools FLow problem. I think that your solution is the correct one because it handle internally the multithreaded requierements and then it continue the business process normally.
2010/4/22 Pedro Maria Buitrago Mantilla <pmbtgun@gmail.com>

The idea is to run multiple independent sub flows. Each of the sub flows requires approximately 2 minutes to complete, so parallel processing is required. Once all the sub flows have completed their tasks is necessary to collect all the results and process them. This implies that the workflow should not end until it collects all information submitted by the sub flows.

For now, I think to create, with JMS, a queue in jboss receive the name of each sub flow, create your own KnowledgeBase run each subflow as a separate workflow and delivers the results. Finally, some components will take all the results (from a database of another jms queue and process and again another component start another workflow to process all results.


PEDRO BUITRAGO
Bogotá, Colombia
2010/4/22 Mauricio Salatino <salaboy@gmail.com>

can you describe a little bit your use case?
I'm not sure about what you want to achieve.
2010/4/21 Pedro Maria Buitrago Mantilla <pmbtgun@gmail.com>
In general, I meet that for resolve the topic of multithreading it's required to implement another thread over a work item.

How does the asynchronic task  can modified a variable of Knowledgebase?

Can you give me an example?

Pedro Buitrago
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