code: def _checkpoint(
      delayed: DelayedSubmission, filepath: Path, countdown: int
  ) -> str:
      """Call the checkpoint method and dump the updated delayed.
  
      Returns:
      --------
          no_requeue_reason: str
              a string explaining while there was no requeuing, else empty string if requeuing works
      """
      logger.get_logger().info("Calling checkpoint method.")
      ckpt_delayed = delayed._checkpoint_function()
      if ckpt_delayed is None:
          return "checkpoint function returned None"
      ckpt_delayed.set_timeout(delayed._timeout_min, countdown)
      with utils.temporary_save_path(filepath) as tmp:
          ckpt_delayed.dump(tmp)
      return ""
  
imports: import os
  import signal
  import socket
  import sys
  import time
  import types
  import typing
  from pathlib import Path
  from .None import logger, utils
  from .utils import DelayedSubmission, JobPaths
label_desc: Use image node_id 1 for calling a global function with example usage: _checkpoint(delayed, filepath, countdown) and returns: str, str