ConcurrentModificationException when Precomputing Inferences

[tobiaswjohn]

I am using Openllet to compute the class hierarchy of an ontology. I discovered a case, where Openllet sometimes throws an exception. This behavior is non-deterministic on my machine, so one may need to test it several times to reproduce the bug.

• The input ontology for which the exception occurs is too large to add it in the text here, but can be found in the following github repository
• Here is the call from my program:

OWLOntologyDocumentSource source = new FileDocumentSource(ontFile, new FunctionalSyntaxDocumentFormat());
OWLOntologyManager manager = OWLManager.createOWLOntologyManager();
OwlOntology ont = manager.loadOntologyFromOntologyDocument(source);

OpenlletReasonerFactory rf = new OpenlletReasonerFactory();
OWLReasoner openllet = rf.createReasoner(ont);

/// precomputation for class hierarchy
if (openllet.isConsistent()) {
 openllet.precomputeInferences(InferenceType.CLASS_HIERARCHY);
}

• the following exception is thrown:

Exception in thread "main" java.util.ConcurrentModificationException
	at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1597)
	at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1620)
	at openllet.core.el.SimplifiedELClassifier.addSuccessor(SimplifiedELClassifier.java:143)
	at openllet.core.el.SimplifiedELClassifier.addSuperClass(SimplifiedELClassifier.java:245)
	at openllet.core.el.SimplifiedELClassifier.processQueue(SimplifiedELClassifier.java:483)
	at openllet.core.el.SimplifiedELClassifier.lambda$classify$1(SimplifiedELClassifier.java:116)
	at openllet.core.utils.Timers.execute(Timers.java:118)
	at openllet.core.el.SimplifiedELClassifier.classify(SimplifiedELClassifier.java:116)
	at openllet.core.KnowledgeBaseImpl.classify(KnowledgeBaseImpl.java:1919)
	at openllet.core.KnowledgeBaseImplFullSync.classify(KnowledgeBaseImplFullSync.java:385)
	at openllet.owlapi.PelletReasoner.precomputeInferences(PelletReasoner.java:1289)