def alltoall_cpu(rank, world_size, output_tensor_list, input_tensor_list):
    """Each process scatters list of input tensors to all processes in a cluster
    and return gathered list of tensors in output list. The tensors should have the same shape.

    Parameters
    ----------
    rank : int
        The rank of current worker
    world_size : int
        The size of the entire communicator
    output_tensor_list : List of tensor
        The received tensors
    input_tensor_list : List of tensor
        The tensors to exchange
    """
    input_tensor_list = [
        tensor.to(th.device("cpu")) for tensor in input_tensor_list
    ]
    for i in range(world_size):
        dist.scatter(
            output_tensor_list[i], input_tensor_list if i == rank else [], src=i
        )
Each process scatters list of input tensors to all processes in a cluster
    and return gathered list of tensors in output list. The tensors should have the same shape.

    Parameters
    ----------
    rank : int
        The rank of current worker
    world_size : int
        The size of the entire communicator
    output_tensor_list : List of tensor
        The received tensors
    input_tensor_list : List of tensor
        The tensors to exchange
    
python/dgl/distributed/optim/pytorch/utils.py