[rules-users] NPE from reteoo.AccumulateNode

[Wolfgang Laun]

Looks like a bug in Drools to me. It has the classic hallmark of a
race condition: the NPE does not happen with every run (on my system),
perhaps only with 85%.

Moreover, with 5.4.0 I get a similar NPE and also:
Exception in thread "main" java.util.NoSuchElementException
	at java.util.LinkedList.remove(LinkedList.java:788)
	at java.util.LinkedList.removeFirst(LinkedList.java:134)
	at org.drools.common.PropagationContextImpl.evaluateActionQueue(PropagationContextImpl.java:344)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:342)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:298)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:123)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:53)
	at overrun.Main.main(Main.java:64)

5.3.0 is the last version without this bug.

-W


On 14/05/2013, jpbarto <Jason.P.Barto at gmail.com> wrote:
> First the specifics: JDK 1.6, Mac OSX, using Drools 5.5 Final
>
> The full source code and rules are pasted below but here's the gist, I have
> a stateful knowledge session to which I am inserting events and running an
> accumulate on the input events.  I have a for loop generating the events
> and
> inserting them as rapidly as possible.  In the rules I use an accumulator
> to
> calculate the average of the values contained within the events.  The
> behavior I'm observing is that if I insert ~120 events without any waiting
> I
> receive an NPE.  If I Thread.sleep for even just 1ms the test goes off
> without a hitch.  Have I uncovered a bug which should be logged in JIRA?  I
> would check through JIRA to see if something similar has been logged but
> I'm
> so unfamiliar with the codebase, not to mention it could all just be user
> error.
>
> The NPE is as follows:
> Exception in thread "main" java.lang.NullPointerException
> 	at
> org.drools.reteoo.AccumulateNode.getFirstMatch(AccumulateNode.java:1050)
> 	at
> org.drools.reteoo.AccumulateNode.modifyLeftTuple(AccumulateNode.java:345)
> 	at
> org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateModifyChildLeftTuple(SingleLeftTupleSinkAdapter.java:259)
> 	at
> org.drools.reteoo.AccumulateNode.evaluateResultConstraints(AccumulateNode.java:676)
> 	at
> org.drools.reteoo.ReteooWorkingMemory$EvaluateResultConstraints.execute(ReteooWorkingMemory.java:590)
> 	at
> org.drools.common.PropagationContextImpl.evaluateActionQueue(PropagationContextImpl.java:350)
> 	at
> org.drools.rule.SlidingLengthWindow.assertFact(SlidingLengthWindow.java:119)
> 	at org.drools.rule.BehaviorManager.assertFact(BehaviorManager.java:94)
> 	at org.drools.reteoo.WindowNode.assertObject(WindowNode.java:167)
> 	at
> org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:497)
> 	at
> org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:382)
> 	at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:235)
> 	at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:240)
> 	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:350)
> 	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:311)
> 	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:127)
> 	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:55)
> 	at drools5fusioneval.Average.main(Average.java:66)
>
> ### Average.java ###
> package drools5fusioneval;
>
> import java.io.IOException;
> import java.util.Random;
> import org.drools.KnowledgeBase;
> import org.drools.KnowledgeBaseConfiguration;
> import org.drools.KnowledgeBaseFactory;
> import org.drools.builder.KnowledgeBuilder;
> import org.drools.builder.KnowledgeBuilderFactory;
> import org.drools.builder.ResourceType;
> import org.drools.conf.EventProcessingOption;
> import org.drools.io.ResourceFactory;
> import org.drools.runtime.StatefulKnowledgeSession;
> import org.drools.runtime.rule.WorkingMemoryEntryPoint;
>
> class AvgDFEChannel implements org.drools.runtime.Channel {
>     @Override
>     public void send(Object o) {
>         System.err.println ("Recieved channel message: "+ o);
>     }
> }
>
> public class Average {
>     public static void main(String[] args) throws InterruptedException,
> IOException {
>         KnowledgeBaseConfiguration kbconfig =
> KnowledgeBaseFactory.newKnowledgeBaseConfiguration();
>         kbconfig.setOption(EventProcessingOption.STREAM);
>
>         KnowledgeBase kbase =
> KnowledgeBaseFactory.newKnowledgeBase(kbconfig);
>
>         KnowledgeBuilder kbuilder =
> KnowledgeBuilderFactory.newKnowledgeBuilder();
>
> kbuilder.add(ResourceFactory.newClassPathResource("drools5fusioneval/average.drl"),
> ResourceType.DRL);
>         if (kbuilder.hasErrors()) {
>             System.err.println(kbuilder.getErrors().toString());
>         }
>         kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());
>
>         final StatefulKnowledgeSession session =
> kbase.newStatefulKnowledgeSession();
>         session.registerChannel("heartbeat", new AvgDFEChannel ());
>         WorkingMemoryEntryPoint ep01 =
> session.getWorkingMemoryEntryPoint("ep01");
>
>         new Thread() {
>             public void run() {
>                 session.fireUntilHalt();
>             }
>         }.start();
>
>         Thread.sleep (5000); // give the engine time to get setup
>
>         Server hiwaesdk = new Server ("hiwaesdk");
>         session.insert(hiwaesdk);
>         long LIMIT = 120;
>         Random rnd = new Random (System.nanoTime());
>
>         for (long i = LIMIT; i > 0; i--) {
>             int j = rnd.nextInt (212);
>             ep01.insert (new IntEvent (j));
>             //Thread.sleep (0x1);
>         }
>
>         System.out.println (hiwaesdk);
>     }
> }
>
>
> ### average.drl ###
> package drools5fusioneval
>
> declare IntEvent
>     @role ( event )
>     @expires(15s)
> end
>
> declare Statistics
>     opsec : long
>     total : long
> end
> global Statistics stats;
>
> rule "Init engine"
>     salience 100
> when
> then
>     stats = new Statistics ();
>     stats.setTotal (0);
>     stats.setOpsec (0);
>     drools.getWorkingMemory ().setGlobal ("stats", stats);
>     System.out.println ("Engine initialized");
> end
>
> rule "number rule"
> when
>     $e : IntEvent () from entry-point ep01
>     $s : Server (hostname == "hiwaesdk")
> then
>     $s.currentTemp = $e.data;
>     stats.setOpsec (stats.getOpsec () + 1);
>     stats.setTotal (stats.getTotal () + 1);
> end
>
> rule "average temp"
> when
>     Number ($avg : intValue) from accumulate (
>             IntEvent ($temp : data) over window:length(10) from entry-point
> ep01, average ($temp)
>         )
>     $s : Server (hostname == "hiwaesdk")
> then
>     $s.avgTemp = $avg;
> end
>
> rule "Heartbeat"
>     timer ( int: 5s 5s)
> when
> then
>     channels["heartbeat"].send ("Heartbeat: "+ stats.getOpsec () / 5 +", "+
> stats.getTotal ());
>     stats.setOpsec (0);
> end
>
>
>
> --
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