async def watch_builders(self):
        """
        Watch builders, run a cleanup function every build_cleanup_interval
        """
        while self.build_cleaner_class:
            cleaner = self.build_cleaner_class(
                kube=self.kube_client, namespace=self.build_namespace, parent=self
            )
            try:
                await asyncio.wrap_future(self.executor.submit(cleaner.cleanup))
            except Exception:
                app_log.exception("Failed to cleanup builders")
            await asyncio.sleep(self.build_cleanup_interval)

        Watch builders, run a cleanup function every build_cleanup_interval
        
binderhub/app.py