class_docstr: An autograd function that performs allgather on a tensor.
code: def backward(ctx, grad_output):
      grad_input = grad_output.clone()
      torch.distributed.all_reduce(
          grad_input, op=torch.distributed.ReduceOp.SUM, async_op=False
      )
      return (
          grad_input[
              ctx.rank
              * ctx.batch_size : (ctx.rank + 1)
              * ctx.batch_size
          ],
          None,
      )
  
imports: import logging
  import torch
  from torch import nn
  import torch.nn.functional
  import math
label_desc: Use image node_id 2 for calling the AllGather2 obj's underlying member method code with example usage: obj.backward(ctx, grad_output) and returns: grad_input,  None