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