code: def rpc_start( working_dir, port, subdomain_index=None, thread=True ):
      
      rpc_srv = BlockstackdRPCServer( working_dir, port, subdomain_index=subdomain_index )
      log.debug("Starting RPC on port {}".format(port))
  
      if thread:
          rpc_srv.start()
  
      return rpc_srv
docs: Start the global RPC server thread
      Returns the RPC server thread