Every inference engine I know about is single-threaded and deterministic. e.g. https://clisprules.net/

With colleagues and friends, I am developing a multi-threaded inference engine, see http://refpersys.org/

If interested by collaboration, contact me (Basile Starynkevitch) by email: at office CEA, LIST (see https://list.cea.fr/ ....) to or at home (near Paris) to [email protected]