[rules-users] Multithreading work items

Mon Apr 26 08:50:47 EDT 2010

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 at gmail.com> 
Sent by: rules-users-bounces at lists.jboss.org
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 at 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 at 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 at 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 at 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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