I have been working through the code with a debugger, it looks like this method call in SingleSessionCommandService is what causes it to behave as if its single threaded:

 

public synchronized <T> T execute(Command<T> command) {

 

The method is synchronized, which I don’t understand – but maybe that is why it is called SingleSessionCommandService. I have tried to work around this by creating a new session every time I need to start a new process but this causes hibernate exceptions of this form:

 

2010/08/31 10:15:58.469{UTC} [AssertionFailure] [ProcessStarterThread-8]:  ERROR: :  an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)

org.hibernate.AssertionFailure: null id in org.drools.persistence.processinstance.ProcessInstanceInfo entry (don't flush the Session after an exception occurs)

                at org.hibernate.event.def.DefaultFlushEntityEventListener.checkId(DefaultFlushEntityEventListener.java:82)

                at org.hibernate.event.def.DefaultFlushEntityEventListener.getValues(DefaultFlushEntityEventListener.java:190)

                at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:147)

                at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:219)

                at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)

                at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)

                at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1206)

                at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:375)

                at org.hibernate.ejb.AbstractEntityManagerImpl$1.beforeCompletion(AbstractEntityManagerImpl.java:1057)

                at bitronix.tm.BitronixTransaction.fireBeforeCompletionEvent(BitronixTransaction.java:430)

                at bitronix.tm.BitronixTransaction.commit(BitronixTransaction.java:173)

                at bitronix.tm.BitronixTransactionManager.commit(BitronixTransactionManager.java:104)

                at org.drools.persistence.session.JtaTransactionManager.commit(JtaTransactionManager.java:164)

                at org.drools.persistence.session.SingleSessionCommandService.execute(SingleSessionCommandService.java:281)

                at org.drools.command.impl.CommandBasedStatefulKnowledgeSession.startProcess(CommandBasedStatefulKnowledgeSession.java:193)

                at org.drools.command.impl.CommandBasedStatefulKnowledgeSession.startProcess(CommandBasedStatefulKnowledgeSession.java:184)

                at drools.test.PersistenceTest.startProcess(PersistenceTest.java:93)

                at drools.test.PersistenceTest.access$1(PersistenceTest.java:92)

                at drools.test.PersistenceTest$1.run(PersistenceTest.java:67)

                at java.lang.Thread.run(Thread.java:619)

 

 

So I am wondering if what I am trying to do is even supported?

 

 

Greg,

 

First of all, thank you very much for you test example.

 

Answering your question:

 

“My question is why when I change the code from running without persistence to running with persistence does it become “single threaded”? You can see by toggling the persistence variable in the top of the test file that when persistence is enabled each flow will complete before the next one begins yet without persistence they run in parallel.”

 

We think the problem is that all the threads are waiting for getting the connection, because of there is only one connection it becomes a shared resource.

 

What do you thing about?

 

Thanks,

 

David.

 

 

 

 

You can download it here:

http://dl.dropbox.com/u/2634115/drools-test.zip

 

You can just import that project into an eclipse workspace and run the unit test, the database should start when you do.

 

I am away until Tuesday next week, if you have any questions I will answer them then.

 

Thanks,

Greg

 

 

Please, could you be so kind to put the whole test project on an http server.

 

I was trying to persist the flow in a PostgreSQL database but I was receiving some Bitronix errors.

 

Have ever of you persist a flow in a database different from h2?

 

Thank at all.

 

David Puigdomenech

 

 

I have written a test based as much as possible on the Drools Flow 5.1 Persistence Documentation. You can see the code here:

 

http://pastebin.com/33QXK4iU

 

And I have attached my eclipse project but without the jars as its too big, if anyone wants a zip of the whole project ready to run, I can put it on an http server for you.

 

My question is why when I change the code from running without persistence to running with persistence does it become “single threaded”? You can see by toggling the persistence variable in the top of the test file that when persistence is enabled each flow will complete before the next one begins yet without persistence they run in parallel.

 

Any advice on what I am doing wrong or whether persistence simply does not support what I want to do is much appreciated.

 

 

Greg

 

 

 

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