code: def _watch_supervisors_from_backend(self):
      raise NotImplementedError
  
file_path: mars/mars/services/cluster/locator.py
imports: import asyncio
  import logging
  from typing import List, Optional
  from ...None import oscar
  from ...lib.uhashring import HashRing
  from .backends import AbstractClusterBackend, get_cluster_backend
  from .core import NodeRole, WatchNotifier
label_desc: Use image node_id 2 for calling the SupervisorLocatorActor obj's underlying member method code with example usage: obj._watch_supervisors_from_backend() without return types