code: def _multi_tensor_copy_this_to_that(this, that, overflow_buf=None):
      """Use multi-tensor-applier to copy values from one list to another.
      We don't have a blfoat16 implementation so for now if the overflow_buf
      is not provided, we default back to simple loop copy to be compatible
      with bfloat16."""
      if overflow_buf:
          overflow_buf.fill_(0)
          # Scaling with factor `1.0` is equivalent to copy.
          multi_tensor_applier(
              amp_C.multi_tensor_scale, overflow_buf, [this, that], 1.0
          )
      else:
          for this_, that_ in zip(this, that):
              that_.copy_(this_)
  
imports: from abc import ABC
  from abc import abstractmethod
  from apex.multi_tensor_apply import multi_tensor_applier
  import amp_C
  import torch
  from megatron import get_timers
  from megatron import print_rank_0
  from megatron.core import mpu, tensor_parallel
  from megatron.model import Float16Module
  from megatron.model.module import param_is_not_shared
  from .clip_grads import clip_grad_norm_fp32, count_zeros_fp32
label_desc: Use image node_id 2 for calling a global function with example usage: _multi_tensor_copy_this_to_that(this, that, overflow_buf) without return types