docstr: Called in MULTIRUN mode before any job starts.
  When using a launcher, this will be executed on local machine before any Sweeper/Launcher is initialized.
code: def on_multirun_start(
      self, config: DictConfig, **kwargs: Any
  ) -> None:
      """
      Called in MULTIRUN mode before any job starts.
      When using a launcher, this will be executed on local machine before any Sweeper/Launcher is initialized.
      """
      ...
  
file_path: hydra/hydra/experimental/callback.py
imports: import logging
  from typing import Any
  from omegaconf import DictConfig
  from hydra.core.utils import JobReturn
  from hydra.types import TaskFunction
label_desc: Use image node_id 3 for calling the Callback obj's underlying member method code with example usage: obj.on_multirun_start(config) without return types