code: def __fire_callback(self, type_, *args, **kwargs):
          
          called = False
          plain_submit = self.__threadpool.submit
          with self.__callbacks:
              submit = self.__crud_threadpool.submit if type_ in _CB_CRUD_TYPES else plain_submit
              for func, serialised_if_crud in self.__callbacks[type_]:
                  called = True
                  # allow CRUD callbacks to not be serialised if requested
                  (submit if serialised_if_crud else plain_submit)(func, *args, **kwargs)
          return called
docs: Returns True if at least one callback was called