class_docstr: A helper class to handle all-reduce operations in a data parallel group.
  A all-reduce collective communication will be operated in
  :func:`handle_gradient` among a data parallel group.
  This class is specialized with ZeRO optimization.
  
  Args:
      model (Module): Model where the gradients accumulate.
      optimizer (Optimizer): Optimizer for updating the parameters.
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docstr: A method running a all-reduce operation in a data parallel group.
docstr_tok: ["A","method","running","a","all-reduce","operation","in","a","data","parallel","group","."]
code: def handle_gradient(self):
      """A method running a all-reduce operation in a data parallel group."""
      self._optimizer.sync_grad()
  
imports: from colossalai.legacy.registry import GRADIENT_HANDLER
  from ._base_gradient_handler import BaseGradientHandler
label_desc: Use image node_id 1 for calling the ZeROGradientHandler obj's underlying member method code with example usage: obj.handle_gradient() without return types