def update_cb(self, context, t, idx, userdata):
        """A sink property changed, calls request_update"""

        if t & PA_SUBSCRIPTION_EVENT_FACILITY_MASK == PA_SUBSCRIPTION_EVENT_SERVER:
            pa_operation_unref(
                pa_context_get_server_info(context, self._server_info_cb, None))

        self.request_update(context)