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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">Hi!</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">We're running drools in a multi-server setup, with a pretty basic scenario:</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">1. When the first session is needed, we load the rulebase once. The rulebase is never changed after this (no rule removal or addition).</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">2. Each call spawns a new StatefulKnowledgeSession which is used for firing the rules once and then disposed. These calls are heavily multi-threaded, but each session is only used
in a single method call from a single thread.</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">3. We use the resource scanner to check for updated packages. When an updated knowledge package is available, the knowledgebase is discarded and a new one constructed from the updated
package.</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">The knowledge package affected is somewhat large - about 25 MB in size. (There are other, smaller knowledge packages which do not appear to have this issue.)</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">This setup has been working fine, but somewhat slow. After upgrading to 5.5.0.Final and adding some speedups in the surrounding code we get a spurious null pointer. The trail of events
is:</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">1. After start all servers work fine.</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">2. Sometime after a couple of hours to a couple of days, the null pointer error occurs on one or more servers (but generally not all of them).</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">3. Once the null pointer occurs, it happens on all further calls using that knowledgebase. No other knowledgebases are effected. (You can load the same package in a new knowledgebase,
and sessions using the new, identical, knowledgebase work just fine.)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">4. Restarting the java process makes the server work fine again.</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">Calls always fail with the same stack trace:</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">org.drools.RuntimeDroolsException: Unexpected exception executing action org.drools.reteoo.ReteooWorkingMemory$WorkingMemoryReteAssertAction@5db53f</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:995)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:335)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:311)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:903)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:847)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:269)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> <stacktrace from our calling code omitted></div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">Caused by: java.lang.NullPointerException</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.rule.EvalCondition.createContext(EvalCondition.java:107)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.EvalConditionNode.createMemory(EvalConditionNode.java:261)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.ConcurrentNodeMemories.createNodeMemory(ConcurrentNodeMemories.java:90)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.ConcurrentNodeMemories.getNodeMemory(ConcurrentNodeMemories.java:69)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.AbstractWorkingMemory.getNodeMemory(AbstractWorkingMemory.java:1034)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.EvalConditionNode.assertLeftTuple(EvalConditionNode.java:174)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:196)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.SingleLeftTupleSinkAdapter.createAndPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:145)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.LeftInputAdapterNode.assertObject(LeftInputAdapterNode.java:154)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:59)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:235)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:240)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.Rete.assertObject(Rete.java:109)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:286)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.reteoo.ReteooWorkingMemory$WorkingMemoryReteAssertAction.execute(ReteooWorkingMemory.java:434)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:993)</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> ... 93 more</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">Unfortunately we don't have the remaining rows in the wrapped exception.</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">From this trace, it looks like the problem is in EvalCondition:</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> public Object createContext() {</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> return this.expression.createContext();</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> }</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">which should only be able to produce a null pointer if expression is missing. Looking at the constructors for this class, having a null expression seems like a valid use case - but
if this is a valid use case, why doesn't createContext() handle this case?</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">Considering that running drools with the same package and the same inputs can either fail with the above error (if knowledgebase has been used enough) or work just as intended (using
a newly minted knowledgebase), it feels like something is corrupting the knowledgebase. Does this make sense?</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">(I noticed in the issue tracker ( https://issues.jboss.org/browse/DROOLS-156 ) that memory for eval nodes are 'created "too lazily"' - might this be a related issue?)</div>
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<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px">Best regards,</div>
<div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="margin:0px"> Anders</div>
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