About: http://webisa.webdatacommons.org/445125641

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	Your implementation seems thread-safe, although you will need to lock when reading from items as well - you can not safely read if there is a concurrent Add operation.
http://www.w3.org/ns/prov#wasQuotedFrom	stackoverflow.com