class_docstr: propagate exceptions to the parent's thread
  refer to https://stackoverflow.com/a/31614591/9601110
class_docstr_tok: ["propagate","exceptions","to","the","parent","'s","thread","refer","to","https",":","\/\/stackoverflow.com\/a\/31614591\/9601110"]
code: def __init__(self, callback=None, idx=-1, **kwargs):
      super().__init__(**kwargs)
      self.callback = callback
      self.idx = idx
  
file_path: byteps/launcher/launch.py
imports: from __future__ import print_function
  import os
  import re
  import subprocess
  import threading
  import sys
  import time
  from functools import reduce
label_desc: Use image node_id 1 to create a new PropagatingThread object from inherited base classes: threading with example: obj = PropagatingThread(callback, idx)