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https://issues.apache.org/jira/browse/JENA-1260?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15670732#comment-15670732
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A. Soroka commented on JENA-1260:
---------------------------------
[~der] you may already know this but if not, you shouldn't need to resubmit:
Github will let you add a commit right in the web interface, using its simple
online editor. If you don't like having multiple commits for this work, they
can be squashed and merged at the same time.
> NullPointerException when using an inferencing model under multithreaded load
> with query and delete
> ---------------------------------------------------------------------------------------------------
>
> Key: JENA-1260
> URL: https://issues.apache.org/jira/browse/JENA-1260
> Project: Apache Jena
> Issue Type: Bug
> Components: Jena
> Affects Versions: Jena 3.0.0
> Reporter: Stephen Owens
> Assignee: Dave Reynolds
> Attachments: TransitiveEngineFailureTest.java
>
>
> {noformat}
> java.lang.NullPointerException
> at java.util.HashSet.contains(HashSet.java:203)
> at
> org.apache.jena.reasoner.transitiveReasoner.TransitiveEngine.triage(TransitiveEngine.java:194)
> at
> org.apache.jena.reasoner.transitiveReasoner.TransitiveEngine.add(TransitiveEngine.java:234)
> at
> org.apache.jena.reasoner.rulesys.FBRuleInfGraph.prepare(FBRuleInfGraph.java:431)
> at
> org.apache.jena.reasoner.BaseInfGraph.requirePrepared(BaseInfGraph.java:530)
> at
> org.apache.jena.reasoner.rulesys.FBRuleInfGraph.findWithContinuation(FBRuleInfGraph.java:557)
> at
> org.apache.jena.reasoner.rulesys.FBRuleInfGraph.graphBaseFind(FBRuleInfGraph.java:587)
> at org.apache.jena.graph.impl.GraphBase.find(GraphBase.java:255)
> at
> org.apache.jena.sparql.engine.iterator.QueryIterTriplePattern$TripleMapper.<init>(QueryIterTriplePattern.java:75)
> at
> org.apache.jena.sparql.engine.iterator.QueryIterTriplePattern.nextStage(QueryIterTriplePattern.java:49)
> at
> org.apache.jena.sparql.engine.iterator.QueryIterRepeatApply.makeNextStage(QueryIterRepeatApply.java:108)
> at
> org.apache.jena.sparql.engine.iterator.QueryIterRepeatApply.hasNextBinding(QueryIterRepeatApply.java:65)
> at
> org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:111)
> at
> org.apache.jena.sparql.engine.iterator.QueryIterBlockTriples.hasNextBinding(QueryIterBlockTriples.java:63)
> at
> org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:111)
> at
> org.apache.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:39)
> at
> org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:111)
> at
> org.apache.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:39)
> at
> org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:111)
> at org.apache.jena.atlas.iterator.Iter$4.hasNext(Iter.java:264)
> at
> org.apache.jena.ext.com.google.common.collect.Iterators$5.hasNext(Iterators.java:547)
> at
> org.apache.jena.test.TransitiveEngineFailureTest$FailureTask.execQuery(TransitiveEngineFailureTest.java:109)
> at
> org.apache.jena.test.TransitiveEngineFailureTest$FailureTask.call(TransitiveEngineFailureTest.java:75)
> at
> org.apache.jena.test.TransitiveEngineFailureTest$FailureTask.call(TransitiveEngineFailureTest.java:1)
> at java.util.concurrent.FutureTask.run(FutureTask.java:266)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
> This failure is due to the
> {{org.apache.jena.reasoner.transitiveReasoner.TransitiveEngine}} class
> declaring the {{subClassAliases}}
> member variable (of type HashSet<Node>) as static. The prepare method
> re-creates this shared variable whenever {{isPrepared}}
> is false:
> {noformat}
> private void prepare() {
> if (isPrepared) return;
> subClassAliases = new HashSet<>();
> . . .
> isPrepared = true;
> }
> {noformat}
> In particular, the static {{subClassAliases}} variable will be re-created
> whenever a {{TransitiveEngine}} object is created
> ({{isPrepared}} is false at creation time). Note that HashSet is neither
> thread-safe nor being accessed in a thread-safe manner.
> The combination of attempting to remove triples from the model and attempting
> to execute queries on the model leads
> to unsafe accesses to {{subClassAliases}}, which eventually leads to a null
> pointer exception.
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