docs: def getObjectId(self):
          """
          Return the object id for this master, for associating state with the
          master.
  
          @returns: ID, via Deferred
          """
          # try to get the cached value
          if self._object_id is not None:
              return defer.succeed(self._object_id)
  
          # failing that, get it from the DB; multiple calls to this function
          # at the same time will not hurt
  
          d = self.db.state.getObjectId(self.name,
                                        "buildbot.master.BuildMaster")
  
          @d.addCallback
          def keep(id):
              self._object_id = id
              return id
          return d