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

["Andy Seaborne (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JENA-1260?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15668537#comment-15668537 ] 

Andy Seaborne edited comment on JENA-1260 at 11/15/16 10:28 PM:
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Thank you for the test case which illustrates the problem when I run it.

I don't see why {{subClassAliases}} and {{subPropertyAliases}} are static.

Removing the "static" seems to make the test case work (5 runs, though it does not fail every time for me when they are static, 50% of the time. So P = 1/32).

[~der]?



was (Author: andy.seaborne):
Than you for the test case.

I don't see why {{subClassAliases}} and {{subPropertyAliases}} are static.

Removing the "static" seems to make the test case work though it does not fail every time for me when they are static.

[~der]?


> 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
>         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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