Claus Stadler created JENA-1861:
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Summary: Query not thread safe
Key: JENA-1861
URL: https://issues.apache.org/jira/browse/JENA-1861
Project: Apache Jena
Issue Type: Question
Components: ARQ
Affects Versions: Jena 3.14.0
Reporter: Claus Stadler
Executing the same query object on different RDFConnections is not thread safe:
I ran into very misleading "NPE in NodeFactory.createLiteral" exceptions when
computing SHA256 sums in parallel on different connections backed by different
datasets/models using the SAME query object.
I identified the cause as due to a race condition due to the digestCache used
in
[ExprDigest|https://github.com/apache/jena/blob/d95b7d295cebaeb2ea41029f4ee7781be94e5e85/jena-arq/src/main/java/org/apache/jena/sparql/expr/ExprDigest.java#L33]
My first question is: Are Query objects - or rather expressions - supposed to
carry execution state or is this rather a bug?
I know that some parts of the Query object, such as result vars, are only
initialized on request which makes use of the same Query object in different
threads fragile to begin with.
So my other question is: Given a Query object, is Jena supposed to allow for
'fully initializing' it, such that its execution using Jena's provided
facilities (models, datasets, etc) is guaranteed to not modify its state?
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