code: def stop(self) -> None:
      if not self.initialized:
          print("The Ray cluster has not been launched.")
          return
      import ray
  
      ray.shutdown()
      self.initialized = False
      with OrcaRayContext._lock:
          OrcaRayContext._active_ray_context = None
  
file_path: BigDL/python/orca/src/bigdl/orca/ray/raycontext.py
imports: import os
  from threading import Lock
  from bigdl.dllib.utils.log4Error import invalidInputError
  from typing import Optional
label_desc: Use image node_id 3 for calling the OrcaRayContext obj's underlying member method code with example usage: obj.stop() without return types