[jira] [Created] (JENA-1260) NullPointerException when using an inferencing model under multithreaded load with query and delete

["Stephen Owens (JIRA)" <ji...@apache.org>]

Stephen Owens created JENA-1260:
-----------------------------------

             Summary: 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


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)

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:

    private void prepare() {
        if (isPrepared) return;
        subClassAliases = new HashSet<>();
        . . .
        isPrepared = true;
    }

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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