[JENA-399] Concurrent execution of SPARQL CONSTRUCT statements against the same Inference Model leads to a ConcurrentModificationException

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Done
• Affects Version/s: Jena 2.10.0
• Fix Version/s: Jena 2.11.0
• Component/s: ARQ, Reasoners
• Labels: InfModel multi-threading race-condition
• Assignee: Rob Vesse
• Reporter: Stephen Owens
• Created: 21/Feb/13 22:46
• Updated: 01/Feb/15 19:11
• Resolved: 01/Feb/15 19:11

Description

Read lock seems to be insufficient for a construct SPARQL query against a model in a multi-threaded situation. See the attached test case for details.

The ConcurrentModificationException is thrown from: LPTopGoalIterator.checkClosed
in com.hp.hpl.jena.reasoner.rulesys.impl.LPTopGoalIterator

Here is a stack trace that shows a path from QueryExecutionBase.
execConstruct() to LPBRuleEngine.checkSafeToUpdate():

LPBRuleEngine.checkSafeToUpdate() line: 223
LPBRuleEngine.deleteAllRules() line: 155
RDFSRuleInfGraph(FBRuleInfGraph).prepare() line: 460
RDFSRuleInfGraph(FBRuleInfGraph).findWithContinuation(TriplePattern, Finder) line: 573
RDFSRuleInfGraph(FBRuleInfGraph).graphBaseFind(Node, Node, Node) line: 605
RDFSRuleInfGraph(GraphBase).find(Node, Node, Node) line: 287
QueryIterTriplePattern$TripleMapper.<init>(Binding, Triple, ExecutionContext) line: 80
QueryIterTriplePattern.nextStage(Binding) line: 53
QueryIterTriplePattern(QueryIterRepeatApply).makeNextStage() line: 115
QueryIterTriplePattern(QueryIterRepeatApply).hasNextBinding() line: 67
QueryIterTriplePattern(QueryIteratorBase).hasNext() line: 113
QueryIterBlockTriples.hasNextBinding() line: 64
QueryIterBlockTriples(QueryIteratorBase).hasNext() line: 113
QueryIterOptionalIndex(QueryIterRepeatApply).makeNextStage() line: 108
QueryIterOptionalIndex(QueryIterRepeatApply).hasNextBinding() line: 67
QueryIterOptionalIndex(QueryIteratorBase).hasNext() line: 113
QueryIteratorCheck(QueryIteratorWrapper).hasNextBinding() line: 40
QueryIteratorCheck(QueryIteratorBase).hasNext() line: 113
QueryIteratorCloseable(QueryIteratorWrapper).hasNextBinding() line: 40
QueryIteratorCloseable(QueryIteratorBase).hasNext() line: 113
Iter$5.hasNext() line: 335
QueryExecutionBase.execConstruct(Model) line: 225
QueryExecutionBase.execConstruct() line: 201

This is a problem because LPBRuleEngine.checkSafeToUpdate() closes all LPTopGoalIterator iterators, some of which are in the middle of processing:

public void checkSafeToUpdate() {
if (!activeInterpreters.isEmpty()) {
ArrayList<LPInterpreterContext> toClose = new ArrayList<LPInterpreterContext>();
for (Iterator<LPInterpreter> i = activeInterpreters.iterator(); i.hasNext(); ) {
LPInterpreter interpreter = i.next();
if (interpreter.getContext() instanceof LPTopGoalIterator)

{ toClose.add(interpreter.getContext()); }

}
for (Iterator<LPInterpreterContext> i = toClose.iterator(); i.hasNext(); )

{ ((LPTopGoalIterator)i.next()).close(); }

}
}