r'''
Utils to play with PyTorch.
'''
import torch.distributed as dist


# pylint: disable=broad-except
# pylint: disable=protected-access
def get_torch_default_comm():
    r'''
    The NCCL communicator is needed so that Fast MoE can perform customized
    communication operators in the C code. However, it is not a publicly
    available variable. Therefore, a hacking class of the `ProcessGroupNCCL`
    in Fast MoE's C code takes the `_default_pg` and tries to dig the
    communicator out from the object. As PyTorch's private interface varies from
    time to time, different hacking techniques are tried one-by-one to be
    compatible with various versions of PyTorch.
    '''
    try:
        comm = dist.distributed_c10d._get_default_group()
        return comm
    except Exception as _:
        pass
    try:
        comm = dist.distributed_c10d._default_pg
        if comm is not None:
            return comm
    except Exception as _:
        pass
    raise RuntimeError('Unsupported PyTorch version')