[rules-dev] Order of retraction matters

[Edson Tirelli]

   Hi Wolfgang,

   Can you please open a JIRA for this.

   It seems the consequence is not properly managing the scope of $m. I.e.,
it must either cache it locally or queue the WMA until it executes
completely.

   Thanks,
       Edson

On Fri, Feb 10, 2012 at 6:52 AM, Wolfgang Laun <wolfgang.laun at gmail.com>wrote:

> 5.3.0 Final.
>
> KnowledgeBase using STREAM, running a stateful session in one thread,
> inserting events from another fact.
>
> class Event{ String name; }
> class Monitor{ Event event; String name; }
>
> rule "start monitoring"
> when
>    $e: Event($name: name)
>    not Monitor( name == $name )
> then
>    insert( new Monitor( $e, $name ) );
> end
>
> rule "timeout"
> timer( int: 10s )
> when
>     $m: Monitor( name == $name )
>     $e: Event($name: name)
> then
>     retract( $m );            // =======================
>     retract( $m.getEvent() );  // ========================
> end
>
> This order of retracts results in a NPE, see the dump below.
>
> Reversing these two works correctly.
>
> Exception in thread "main" Exception executing consequence for rule "start
> monitoring" in hashcode: java.lang.NullPointerException
> at
> org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39)
>  at
> org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1101)
> at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1029)
>  at org.drools.common.DefaultAgenda.fireUntilHalt(DefaultAgenda.java:1229)
> at
> org.drools.common.AbstractWorkingMemory.fireUntilHalt(AbstractWorkingMemory.java:753)
>  at
> org.drools.common.AbstractWorkingMemory.fireUntilHalt(AbstractWorkingMemory.java:729)
> at
> org.drools.impl.StatefulKnowledgeSessionImpl.fireUntilHalt(StatefulKnowledgeSessionImpl.java:234)
>  at hashcode.Main.execute(Main.java:148)
> at hashcode.Main.main(Main.java:206)
> Caused by: java.lang.NullPointerException
> at
> org.drools.base.hashcode.StateEvent42211789$getItemName.getValue(Unknown
> Source)
> at org.drools.base.ClassFieldReader.getValue(ClassFieldReader.java:87)
>  at org.drools.rule.Declaration.getValue(Declaration.java:219)
> at
> hashcode.Rule_start_monitoringDefaultConsequenceInvoker.evaluate(Unknown
> Source)
>  at
> org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1091)
> ... 7 more
>
>
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>


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