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https://issues.apache.org/jira/browse/JENA-1861?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17059073#comment-17059073
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Claus Stadler commented on JENA-1861:
-------------------------------------
Here is example code that should eventually die due to a race condition, for me
it takes a few seconds:
{code}
@Test
public void testRaceCondition() {
Stream.generate(() -> QueryFactory.create("SELECT * {
BIND(SHA256('foo') AS ?bar) }"))
.peek(q -> q.setResultVars()) // <-- With this line commented out,
the race condition happens earlier
// Repeat q to increase chance to cause the race condition
.forEach(q -> Arrays.asList(q, q, q, q, q, q, q, q).parallelStream()
.forEach(query -> {
Model model = ModelFactory.createDefaultModel();
try(QueryExecution qe = QueryExecutionFactory.create(query,
model)) {
ResultSetFormatter.consume(qe.execSelect());
}
}));
}
{code}
> 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
> Priority: Major
>
> 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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