code: def register_callback_handler(
      event_name: str,
      callback: Union[
          Callable[[Dict], None], List[Callable[[Dict], None]]
      ],
  ) -> None:
      """Registers a callback handler for autoscaler events.
  
      Args:
          event_name: Event that callback should be called on. See
              CreateClusterEvent for details on the events available to be
              registered against.
          callback: Callable object that is invoked
              when specified event occurs.
      """
      global_event_system.add_callback_handler(event_name, callback)
  
imports: import json
  import os
  import tempfile
  from contextlib import contextmanager
  from typing import Any, Callable, Dict, Iterator, List, Optional, Union
  from ray.autoscaler._private import commands
  from ray.autoscaler._private.cli_logger import cli_logger
  from ray.autoscaler._private.event_system import CreateClusterEvent
  from ray.autoscaler._private.event_system import global_event_system
  from ray.util.annotations import DeveloperAPI
label_desc: Use image node_id 12 for calling a global function with example usage: register_callback_handler(event_name, callback) without return types