Steve,

   What versions of MVEL and Drools are you using?
   Comments:

* You can not share packages between rulebases. You can share rulebases among sessions. So, I strongly advise you to change your application to build the rulebase once, and have the web sessions only create the rule session every time... not the whole rulebase. Since packages have their own classloaders and everytime you create a rulebase you merge such classloaders, the problem might happen (CCE) exactly at the time you are creating the rulebase concurrently. Drools 5 allows you to share packages, although I still prefer to not do it and share only the rulebase.

* You can not use collect in this case, because you are creating a list of $slot, not a list of PotentialMatch. Although, it is extremely easy to create an accumulate function for that. Drools 5 includes 2 accumulate functions: collectSet and collectList for that. If you want, just get the class from Drools 5, fix the imports to use the classes from Drools 4 and use it. Except for the "imports" you should not have any problem. Your rule would look like:


rule "My Rule"
    salience 50
    dialect "java"
    no-loop true
    when
        $module : Module( selected == false, required > 1, $size : required )
        $list : List( )
                from accumulate( PotentialMatch( module == $module, $slot : slot ),
                    collectList( $slot ) )
        eval( countThem($list, $size) != $module.setMatchCount() )
    then
        modify( $module ) { setMatchCount(countThem($list, $size)) };
end

* Finally, your eval looks odd to me, but anyway, don't have enough details to advise you on that.


    []s
    Edson


2009/6/23 Steve Ronderos <steve.ronderos@ni.com>

Hi Rules Users,

I'm experiencing an issue with a Drools 4.0.7 rule.

Here is a clip of the exception that is thrown:

Caused by: org.mvel.CompileException: cannot invoke method
        at org.mvel.optimizers.impl.refl.MethodAccessor.getValue(MethodAccessor.java:54)
        at org.mvel.optimizers.impl.refl.VariableAccessor.getValue(VariableAccessor.java:39)
        at org.mvel.ast.VariableDeepPropertyNode.getReducedValueAccelerated(VariableDeepPropertyNode.java:22)
        at org.mvel.ast.PropertyASTNode.getReducedValueAccelerated(PropertyASTNode.java:21)
        at org.mvel.MVELRuntime.execute(MVELRuntime.java:90)
        at org.mvel.CompiledExpression.getValue(CompiledExpression.java:111)
        at org.mvel.MVEL.executeExpression(MVEL.java:235)
        at org.drools.base.mvel.MVELConsequence.evaluate(MVELConsequence.java:48)
        at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:554)
        ... 80 more
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.GeneratedMethodAccessor412.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at org.mvel.optimizers.impl.refl.MethodAccessor.getValue(MethodAccessor.java:46)
        ... 88 more
Caused by: org.drools.RuntimeDroolsException: java.lang.ClassCastException: com.demo.Rule_My_Rule_0$Accumulate0
        at org.drools.rule.Accumulate.accumulate(Accumulate.java:131)
        at org.drools.reteoo.AccumulateNode.modifyTuple(AccumulateNode.java:352)
        at org.drools.reteoo.AccumulateNode.assertObject(AccumulateNode.java:248)
        at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:318)
        at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:162)
        at org.drools.reteoo.Rete.assertObject(Rete.java:175)
        at org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:192)
        at org.drools.reteoo.ReteooWorkingMemory.doInsert(ReteooWorkingMemory.java:71)
        at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:911)
        at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:883)
        at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:67)
        at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:61)
        ... 92 more
Caused by: java.lang.ClassCastException: com.demo.Rule_My_Rule_0$Accumulate0
        at com.demo.Rule_My_Rule_0Accumulate0Invoker.accumulate(Rule_My_Rule_0Accumulate0Invoker.java:43)
        at org.drools.rule.Accumulate.accumulate(Accumulate.java:123)
        ... 103 more

The actually rule name and package are a lot longer, I changed them here for brevity and because I don't believe the names themselves are relevant.

This exception is being thrown intermittently when this rule, which contains an accumulate function is called.  I say intermittently because it does not happen every time the rule is run.  As far as I can tell the ClassCastExceptions only happens when the computer that the rules are running on is under load.

A few more details before I post the rule itself.  The rule base that I am building consists of 2 drl files.  Both of the files have the same package declaration at the top.  The 2 packages are built separately using PackageBuilder then combined using RuleBase.addPackage() on both packages.  Also, I'm not sure if this is relevant, but this scenario takes place in a web application where the two package objects are only built once (for performance) but each user session creates a new RuleBase and adds the packages.  The individual sessions then create stateful sessions from the rule base.

This is the rule that I believe is causing the issue.

rule "My Rule"
    salience 50
    dialect "java"
    no-loop true
    when
        $module : Module( selected == false, required > 1, $size : required )
        $list : ArrayList( )
                from accumulate( PotentialMatch( module == $module, $slot : slot ),
                    init( List result = new ArrayList(); ),
                    action( result.add($slot); ),
                    reverse( result.remove((Integer)$slot ); ),
                    result( result ) )
        eval( countThem($list, $size) != $module.setMatchCount() )
    then
        modify( $module ) { setMatchCount(countThem($list, $size)) };
end

As I'm typing this I realize that there is another way to write this rule using collect.  I'm not sure why it was written this way, but since I have already come this far, has anyone had any experience with the Drools 4 generated code throwing ClassCastExceptions?

Thanks,

Steve Ronderos
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users




--
 Edson Tirelli
 JBoss Drools Core Development
 JBoss by Red Hat @ www.jboss.com