[rules-users] Question about custom accumulation functions

[Bruno Freudensprung]

Hi Edson, hi all,

To stick to the subject, I have a strange problem (stack trace in PS) 
with a rule containing two accumulate calls, the result of the first one 
is re-injected as the input of the second one. Those accumulate 
functions are "home made".
The first one (tokenize) returns an ArrayList of Token objects built by 
tokenizing the "text" of the Sentence objects.
The second one (build10windows) returns an ArrayList of Window objects, 
each one them containing 10 consecutive tokens.
Here is the rule

     when
         $budget : ManualAnnotation(text == "something")
*$tokens* : java.util.ArrayList() *from accumulate *($s : Sentence(), 
*tokenize*($s))
         $windows : java.util.ArrayList() *from accumulate *($t : 
Token() *from $tokens*, *build10windows*($t))
         # removed a part here but the problem occurs even without this part
     then
         retract($budget);

Is there anything else one should be aware of when implementing their 
own accumulate function? I mean things related to the fact that 
"classical" accumulate functions (sum, average) return an immutable 
object that does not share anything with the context object.
Although accumulate, reverse, and getResult methods of my functions are 
unit tested, I suspect something that could be related to 
stateless/stateful considerations.
What do you think?

Many thanks,

Bruno.

PS :

The stack trace is:
     at 
org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39)
     at 
org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:927)
     at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:856)
     at 
org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1071)
     at 
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:785)
     at 
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:751)
     at 
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:218)
     at 
org.drools.command.runtime.rule.FireAllRulesCommand.execute(FireAllRulesCommand.java:99)
     at 
org.drools.command.runtime.rule.FireAllRulesCommand.execute(FireAllRulesCommand.java:33)
     at 
org.drools.command.runtime.BatchExecutionCommandImpl.execute(BatchExecutionCommandImpl.java:159)
     at 
org.drools.command.runtime.BatchExecutionCommandImpl.execute(BatchExecutionCommandImpl.java:81)
     at 
org.drools.impl.StatelessKnowledgeSessionImpl.execute(StatelessKnowledgeSessionImpl.java:262)
     ... 5 more
Caused by: java.lang.NullPointerException
     at 
org.drools.reteoo.AccumulateNode.getFirstMatch(AccumulateNode.java:967)
     at org.drools.reteoo.AccumulateNode.splitList(AccumulateNode.java:920)
     at 
org.drools.reteoo.AccumulateNode.removePreviousMatchesForLeftTuple(AccumulateNode.java:874)
     at 
org.drools.reteoo.AccumulateNode.retractLeftTuple(AccumulateNode.java:205)
     at 
org.drools.reteoo.CompositeLeftTupleSinkAdapter.doPropagateRetractLeftTuple(CompositeLeftTupleSinkAdapter.java:238)
     at 
org.drools.reteoo.CompositeLeftTupleSinkAdapter.propagateRetractLeftTupleDestroyRightTuple(CompositeLeftTupleSinkAdapter.java:138)
     at 
org.drools.reteoo.AccumulateNode.retractLeftTuple(AccumulateNode.java:212)
     at 
org.drools.reteoo.ObjectTypeNode.retractObject(ObjectTypeNode.java:240)
     at 
org.drools.reteoo.EntryPointNode.retractObject(EntryPointNode.java:231)
     at 
org.drools.common.AbstractWorkingMemory.retract(AbstractWorkingMemory.java:1288)
     at 
org.drools.base.DefaultKnowledgeHelper.retract(DefaultKnowledgeHelper.java:201)
     at 
org.drools.base.DefaultKnowledgeHelper.retract(DefaultKnowledgeHelper.java:214)
     at 
defaultpkg.Rule_Display_windows_0.defaultConsequence(Rule_Display_windows_0.java:21)
     at 
defaultpkg.Rule_Display_windows_0DefaultConsequenceInvoker.evaluate(Rule_Display_windows_0DefaultConsequenceInvoker.java:29)
     at 
org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:917)
     ... 15 more


Bruno.

Le 24/08/2011 16:21, Edson Tirelli a écrit :
>
>    Yes, evaluation is incremental, so for every new fact, it will call 
> accumulate() and getResult().
>
>    We do want to reduce the calls to getResult(), improving 
> performance, but it is not easy to figure out a way, as from an engine 
> perspective, it never knows when the application is done inserting 
> facts and it is time to calculate the final result.
>
>    Edson
>
> 2011/8/24 Bruno Freudensprung <bruno.freudensprung at temis.com 
> <mailto:bruno.freudensprung at temis.com>>
>
>     Hi,
>
>     While testing my custom accumulation function I noticed an unexpected
>     behavior (th'ats of course a personal point of view).
>     It seems that Drools 5.1 calls accumulate(...) and getResult(...) as
>     many times as the number of accumulated facts (accumulate, getResult,
>     accumulate, getResult, etc...).
>     Is it supposed to work like this?
>
>     Best regards,
>
>     Bruno.
>
>     _______________________________________________
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>
>
>
>
> -- 
>   Edson Tirelli
>   JBoss Drools Core Development
>   JBoss by Red Hat @ www.jboss.com <http://www.jboss.com>
>
>
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