The following rule produces a memory leak in Drools 6.1.0-SNAPSHOT:

(Stream mode)

declare MyEvent 

  @role(event) 

  @timestamp(timestamp) 

end

/* If a RAISE is buffered for N seconds, send it out */

rule "forward raise"

	no-loop

	duration (3s)

when

	$raise : MyEvent(eventState == EventState.RAISE, $raiseId : eventId)

then

	System.out.println("Forwarding RAISE(" + $raiseId + ")");

	delete($raise);

end

I see the rule fire as expected, printing out the message 3 seconds after the event is added into the session. While the event is waiting, I see a FactCount of 1 in the session. After the rule fires, the fact count goes to 0. However, using JVisualVm, querying the heap dump shows 1 instance of MyEvent, referenced by an EventFactHandle and several other Drools objects.

Is this a bug, or is there a better way to write this rule so Drools’ internals let go of the object after it is no longer a fact?