code: def _get_or_create_router(
      self,
  ) -> Union[Router, asyncio.AbstractEventLoop]:
      if self._router is None:
          node_id = ray.get_runtime_context().get_node_id()
          try:
              cluster_node_info_cache = create_cluster_node_info_cache(
                  GcsClient(
                      address=ray.get_runtime_context().gcs_address
                  )
              )
              cluster_node_info_cache.update()
              availability_zone = cluster_node_info_cache.get_node_az(
                  node_id
              )
          except Exception:
              availability_zone = None
  
          self._router = Router(
              serve.context._get_global_client()._controller,
              self.deployment_id,
              node_id,
              get_current_actor_id(),
              availability_zone,
              event_loop=_create_or_get_global_asyncio_event_loop_in_thread(),
              _prefer_local_node_routing=self.handle_options._prefer_local_routing,
              _router_cls=self.handle_options._router_cls,
          )
  
      return self._router, self._router._event_loop
  
imports: import asyncio
  import concurrent.futures
  import threading
  import warnings
  from dataclasses import dataclass
  from typing import Any, AsyncIterator, Dict, Iterator, Optional, Tuple, Union
  import ray
  from ray import serve
  from ray._raylet import GcsClient, ObjectRefGenerator
  from ray.serve._private.common import DeploymentID, RequestProtocol
  from ray.serve._private.default_impl import create_cluster_node_info_cache
  from ray.serve._private.router import RequestMetadata, Router
  from ray.serve._private.usage import ServeUsageTag
  from ray.serve._private.utils import DEFAULT, get_current_actor_id, get_random_string, is_running_in_asyncio_loop
  from ray.util import metrics
  from ray.util.annotations import Deprecated, DeveloperAPI, PublicAPI
label_desc: Use image node_id 4 for calling the _DeploymentHandleBase obj's underlying member method code with example usage: obj._get_or_create_router() and returns: self,  self