class_docstr: _SerialMessage wraps a payload in a monotonically-increasing serial number, which makes it easy
  to confirm that our broadcasting does not get out-of-sync.
class_docstr_tok: ["_SerialMessage","wraps","a","payload","in","a","monotonically-increasing","serial","number",",","which","makes","it","easy","to","confirm","that","our","broadcasting","does","not","get","out-of-sync","."]
code: def __init__(self, serial: int, payload: Any) -> None:
      self.serial = serial
      self.payload = payload
  
imports: import logging
  import os
  import selectors
  import signal
  import socket
  import subprocess
  import time
  from typing import Any, Callable, Dict, List, Optional, Tuple, Union
  import determined
label_desc: Use image node_id 1 to create a new _SerialMessage object  with example: obj = _SerialMessage(serial, payload)