[rules-users] Help with troubleshooting rules/Drools

Richard Calmbach rcalmbac at gmail.com
Tue Nov 1 01:10:38 EDT 2011 

Robert Crawford wrote:
> 
> Any advice on how to troubleshoot problems? I have a fairly simple set of
> rules (a couple dozen), but keep having problems with fatal exceptions.
> The most recent was:
> 
> org.drools.RuntimeDroolsException: Unexpected exception executing action
> org.drools.reteoo.PropagationQueuingNode$PropagateAction at 1e60aa7
>      at
> org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:977)
>      at
> org.drools.common.DefaultAgenda.fireUntilHalt(DefaultAgenda.java:1231)
>      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
> com.kroger.tempmonitor.app.service.RuleService$1.run(RuleService.java:214)
>      at java.lang.Thread.run(Thread.java:662)
> Caused by: java.util.NoSuchElementException
>      at java.util.LinkedList.remove(LinkedList.java:788)
>      at java.util.LinkedList.removeFirst(LinkedList.java:134)
>      at
> org.drools.common.PropagationContextImpl.evaluateActionQueue(PropagationContextImpl.java:264)
>      at
> org.drools.reteoo.PropagationQueuingNode$AssertAction.execute(PropagationQueuingNode.java:357)
>      at
> org.drools.reteoo.PropagationQueuingNode.propagateActions(PropagationQueuingNode.java:238)
>      at
> org.drools.reteoo.PropagationQueuingNode$PropagateAction.execute(PropagationQueuingNode.java:502)
>      at
> org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:975)
>      ... 6 more
> 
> 
> No mention of a rule name, so where do I begin?
> 

The exception may happen during working memory operations (e.g., an insert),
so there isn't even a rule active.

Which version of Drools are you using? In my case, switching from Drools
5.2.0.Final to Drools 5.3.0.Final broke 47 of my unit tests (1 error and 46
failures). The one that now gives an error, shows this stacktrace (similar
to yours):

org.drools.RuntimeDroolsException: Unexpected exception executing action
org.drools.reteoo.PropagationQueuingNode$PropagateAction at 7a9b777a
	at
org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:977)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:315)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:291)
	at
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:886)
	at
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:845)
	at
org.drools.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:255)
	at com.acme.das.fraud.RulesTestBase.sendEot(RulesTestBase.java:139)
	at com.acme.das.fraud.RulesTestBase.advanceTime(RulesTestBase.java:131)
	at com.acme.das.fraud.RulesTestBase.advanceTime(RulesTestBase.java:135)
	at
com.acme.das.fraud.RulesTest.testUdrAndThenStartCdrWithinTimeout(RulesTest.java:1061)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:66)
	at org.jmock.integration.junit4.JMock$1.invoke(JMock.java:37)
	at
org.junit.internal.runners.MethodRoadie.runTestMethod(MethodRoadie.java:105)
	at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:86)
	at
org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:94)
	at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:84)
	at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
	at
org.junit.internal.runners.JUnit4ClassRunner.invokeTestMethod(JUnit4ClassRunner.java:98)
	at
org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:61)
	at
org.junit.internal.runners.JUnit4ClassRunner$1.run(JUnit4ClassRunner.java:54)
	at
org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34)
	at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44)
	at
org.junit.internal.runners.JUnit4ClassRunner.run(JUnit4ClassRunner.java:52)
	at
org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)
	at
org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
	at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
	at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
	at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: java.lang.NullPointerException
	at java.util.PriorityQueue.siftUpComparable(PriorityQueue.java:582)
	at java.util.PriorityQueue.siftUp(PriorityQueue.java:574)
	at java.util.PriorityQueue.removeAt(PriorityQueue.java:550)
	at java.util.PriorityQueue.remove(PriorityQueue.java:309)
	at
org.drools.time.impl.PseudoClockScheduler.removeJob(PseudoClockScheduler.java:147)
	at org.drools.common.Scheduler.removeAgendaItem(Scheduler.java:74)
	at
org.drools.common.DefaultAgenda.removeScheduleItem(DefaultAgenda.java:543)
	at
org.drools.common.ScheduledAgendaItem.remove(ScheduledAgendaItem.java:91)
	at
org.drools.reteoo.RuleTerminalNode.retractLeftTuple(RuleTerminalNode.java:385)
	at
org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateRetractLeftTuple(SingleLeftTupleSinkAdapter.java:225)
	at
org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateRetractLeftTuple(SingleLeftTupleSinkAdapter.java:99)
	at org.drools.reteoo.NotNode.propagateRetractLeftTuple(NotNode.java:453)
	at org.drools.reteoo.NotNode.assertObject(NotNode.java:148)
	at
org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:59)
	at
org.drools.reteoo.PropagationQueuingNode$AssertAction.execute(PropagationQueuingNode.java:354)
	at
org.drools.reteoo.PropagationQueuingNode.propagateActions(PropagationQueuingNode.java:238)
	at
org.drools.reteoo.PropagationQueuingNode$PropagateAction.execute(PropagationQueuingNode.java:502)
	at
org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:975)
	... 32 more

Also, upgrading to Drools 5.3.0.Final is breaking my functional tests, too
(real-time clock!). It's difficult to narrow down just what broke in Drools
5.3.0, but there seems to be a theme having to do with the session clock and
timer service. In the unit tests, it seems none of the events after the
first one get inserted. I'm using an event feeder based on the Fusion Broker
example.

If you haven't already, try running your code with Drools 5.2.0, just to get
another data point.



> My architecture is simple: one thread ran fireUntilHalt(), other
> (multiple) threads inserting objects. Should I synchronize on the session
> so only one thread is inserting at a time?
> 

I have definitely seen incorrect behavior when having multiple threads
insert events concurrently. Under certain limited conditions, it may be
possible to run multithreaded inserts on the same session, but in the
general case this is not guaranteed to work (empirically established). If
your processing can be split into completely independent event streams, you
can process each stream in its own knowledge session (in its own thread,
hence giving you parallelism), but within each stream (or among a set of
correlated streams, say events from one client), inserts need to be
serialized by synchronizing on the session, otherwise you can get incorrect
behavior (I know I did!). In a nutshell: Rule consequences are not executed
atomically.



> There's one rule that triggers a large number of inserts, and it used to
> give me problems, but I've moved those inserts into Commands and those
> problems seem to have gone away.
> 
> Any advice would be welcome, no matter how basic you think it is! Thanks!
> 


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