When loading an ontology with imports, the ClerezzaOntologyProvider keeps triple iterators running on the target graph for longer than required. Since Clerezza introduced Lockable the MGraph, this thread-unsafety has resulted in concurrent exceptions being thrown.
The solution is now to
- minimize the lifetime of iterators (do not keep them open during import resolution)
- use mutex locks as documented in https://clerezza.apache.org/faq/