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