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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