def __fire_callback(self, type_, *args, **kwargs):
        """Returns True if at least one callback was called"""
        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
Returns True if at least one callback was called