class_docstr: This defines a join hook, which provides two entry points in the join context manager.
  
  Entry points : a main hook, which is called repeatedly while there exists a non-joined
  process, and a post-hook, which is called once all processes have joined.
  
  To implement a join hook for the generic join context manager, define a
  class that inherits from :class:`JoinHook` and override ``main_hook()`` and
  ``post_hook()`` as appropriate.
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docstr: Call hook after all processes have joined.
  
  It is passed an additional ``bool`` argument ``is_last_joiner``, which indicates if the rank is one of the last to join.
  
  Arguments:
      is_last_joiner (bool): ``True`` if the rank is one of the last to
          join; ``False`` otherwise.
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code: def post_hook(self, is_last_joiner: bool) -> None:
      r"""
      Call hook after all processes have joined.
  
      It is passed an additional ``bool`` argument ``is_last_joiner``, which indicates if the rank is one of the last to join.
  
      Arguments:
          is_last_joiner (bool): ``True`` if the rank is one of the last to
              join; ``False`` otherwise.
      """
      ...
  
imports: import warnings
  from abc import ABC, abstractmethod
  from types import TracebackType
  from typing import Any, List, NamedTuple, Optional, Type
  import torch
  import torch.distributed
label_desc: Use image node_id 2 for calling the JoinHook obj's underlying member method code with example usage: obj.post_hook(is_last_joiner) without return types