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https://issues.apache.org/jira/browse/JENA-824?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14235368#comment-14235368
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Andy Seaborne commented on JENA-824:
------------------------------------
It looks like Query.setResultVars is not called at the end of parsing in
{{ParserSPARQL11.parse$}} and related classes, or may be {{SPARQLParser}} which
calls {{parse$}}.
Once flag {{resultVarsSet}} is set, it should be thread safe.
I think we should avoid synchronized on any get/read operations because of
multuithreaded use. The contract should be "create-seal-use", where "use" is
multithreaded on an unchanging object.
> Concurrent usage of query causes NPE
> ------------------------------------
>
> Key: JENA-824
> URL: https://issues.apache.org/jira/browse/JENA-824
> Project: Apache Jena
> Issue Type: Bug
> Reporter: Kristian Rosenvold
>
> Callin gQueryFactory.parse and then handling the Query off to multiple
> threads can/will cause the error show in the stacktrace.
> As long as setResultVars is called on the Query before handing off to
> threads, it seems to be safe.
> Pull request is coming on this.
> java.lang.NullPointerException
> at com.hp.hpl.jena.sparql.core.Var.varNames(Var.java:193)
> at com.hp.hpl.jena.query.Query.getResultVars(Query.java:369)
> at
> com.hp.hpl.jena.sparql.engine.QueryExecutionBase.asResultSet(QueryExecutionBase.java:470)
> at
> com.hp.hpl.jena.sparql.engine.QueryExecutionBase.execResultSet(QueryExecutionBase.java:533)
> at com.hp.hpl.jena.sparql.engine.QueryExecutionBase.execSelect
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