[jira] [Created] (JENA-1861) Query not thread safe

["Claus Stadler (Jira)" <ji...@apache.org>]

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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