docstr: Perform an optimizer step.
  
  This step updates the joined process's shard of
  the parameters and broadcasts those parameters.
docstr_tok: ["Perform","an","optimizer","step",".","This","step","updates","the","joined","process","'s","shard","of","the","parameters","and","broadcasts","those","parameters","."]
code: def main_hook(self):
      """
      Perform an optimizer step.
  
      This step updates the joined process's shard of
      the parameters and broadcasts those parameters.
      """
      self.zero.step()
  
imports: import collections
  import copy
  import enum
  import inspect
  import io
  import logging
  from itertools import chain
  from typing import Any, Callable, Dict, List, Optional, Set, Type, Union
  import torch
  import torch.distributed
  from torch.distributed.algorithms.join import Join, Joinable, JoinHook
  from torch.distributed.optim.utils import functional_optim_map
  from torch.optim import Optimizer
label_desc: Use image node_id 2 for calling the _ZeROJoinHook obj's underlying member method code with example usage: obj.main_hook() without return types