code: def _prepare_allreduce_pack_buffer(
      self, allreduce_grad_dtype, n_elems
  ):
      allreduce_grad_n_bytes = allreduce_grad_dtype.itemsize * n_elems
      needs_sync = False
  
      if self.gpu_buffer_a.size != allreduce_grad_n_bytes:
          self.gpu_buffer_a.assign(allreduce_grad_n_bytes)
          needs_sync = True
      if self.gpu_buffer_b.size != allreduce_grad_n_bytes:
          self.gpu_buffer_b.assign(allreduce_grad_n_bytes)
          needs_sync = True
  
      return needs_sync
  
file_path: chainer/chainermn/communicators/pure_nccl_communicator.py
imports: import warnings
  import chainer.cuda
  from chainermn.communicators import _communication_utility
  from chainermn.communicators import _memory_utility
  from chainermn.communicators import mpi_communicator_base
  from chainermn import nccl
  import numpy
label_desc: Use image node_id 9 for calling the PureNcclCommunicator obj's underlying member method code with example usage: obj._prepare_allreduce_pack_buffer(allreduce_grad_dtype, n_elems) and returns: needs_sync