About: http://webisa.webdatacommons.org/269088908

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	@Andrew: Actually, having read the question a third time, my original answer was still useful: the OP was asking whether the code in the question was thread safe, not the code including the synchronization.
http://www.w3.org/ns/prov#wasQuotedFrom	stackoverflow.com