torch/distributed/rpc/options.py

from torch._C._distributed_rpc import _TensorPipeRpcBackendOptionsBase
from . import constants as rpc_contants

import torch

from typing import Dict, List


class TensorPipeRpcBackendOptions(_TensorPipeRpcBackendOptionsBase):
    r"""
    The backend options for
    :class:`~torch.distributed.rpc.TensorPipeAgent`, derived from
    :class:`~torch.distributed.rpc.RpcBackendOptions`.

    Args:
        num_worker_threads (int, optional): The number of threads in the
            thread-pool used by
            :class:`~torch.distributed.rpc.TensorPipeAgent` to execute
            requests (default: 16).
        rpc_timeout (float, optional): The default timeout, in seconds,
            for RPC requests (default: 60 seconds). If the RPC has not
            completed in this timeframe, an exception indicating so will
            be raised. Callers can override this timeout for individual
            RPCs in :meth:`~torch.distributed.rpc.rpc_sync` and
            :meth:`~torch.distributed.rpc.rpc_async` if necessary.
        init_method (str, optional): The URL to initialize the distributed
            store used for rendezvous. It takes any value accepted for the
            same argument of :meth:`~torch.distributed.init_process_group`
            (default: ``env://``).
        device_maps (Dict[str, Dict]): Device placement mappings from this
            worker to the callee. Key is the callee worker name and value the
            dictionary (``Dict`` of ``int``, ``str``, or ``torch.device``) that
            maps this worker's devices to the callee worker's devices.
            (default: ``None``)
    """
    def __init__(
        self,
        *,
        num_worker_threads: int = rpc_contants.DEFAULT_NUM_WORKER_THREADS,
        rpc_timeout: float = rpc_contants.DEFAULT_RPC_TIMEOUT_SEC,
        init_method: str = rpc_contants.DEFAULT_INIT_METHOD,
        device_maps: Dict = None,
        _transports: List = None,
        _channels: List = None,
    ):
        super().__init__(
            num_worker_threads,
            _transports,
            _channels,
            rpc_timeout,
            init_method,
            device_maps if device_maps else {}
        )

    def set_device_map(self, to: str, device_map: Dict):
        r"""
        Set device mapping between each RPC caller and callee pair. This
        function can be called multiple times to incrementally add
        device placement configurations.

        Args:
            worker_name (str): Callee name.
            device_map (Dict of int, str, or torch.device): Device placement
                mappings from this worker to the callee. This map must be
                invertible.

        Example::
            >>> # both workers
            >>> def add(x, y):
            >>>     print(x)  # tensor([1., 1.], device='cuda:1')
            >>>     return x + y, (x + y).to(2)
            >>>
            >>> # on worker 0
            >>> options = TensorPipeRpcBackendOptions(
            >>>     num_worker_threads=8,
            >>>     device_maps={"worker1": {0: 1}}
            >>>     # maps worker0's cuda:0 to worker1's cuda:1
            >>> )
            >>> options.set_device_map("worker1", {1: 2})
            >>> # maps worker0's cuda:1 to worker1's cuda:2
            >>>
            >>> rpc.init_rpc(
            >>>     "worker0",
            >>>     rank=0,
            >>>     world_size=2,
            >>>     backend=rpc.BackendType.TENSORPIPE,
            >>>     rpc_backend_options=options
            >>> )
            >>>
            >>> x = torch.ones(2)
            >>> rets = rpc.rpc_sync("worker1", add, args=(x.to(0), 1))
            >>> # The first argument will be moved to cuda:1 on worker1. When
            >>> # sending the return value back, it will follow the invert of
            >>> # the device map, and hence will be moved back to cuda:0 and
            >>> # cuda:1 on worker0
            >>> print(rets[0])  # tensor([2., 2.], device='cuda:0')
            >>> print(rets[1])  # tensor([2., 2.], device='cuda:1')
        """
        device_index_map = {}
        curr_device_maps = super().device_maps
        for k in device_map:
            v = device_map[k]
            k, v = torch.device(k), torch.device(v)
            if k.type != 'cuda' or v.type != 'cuda':
                raise ValueError(
                    "`set_device_map` only supports CUDA devices, "
                    f"but got device pair {k}: {v}"

                )
            if to in curr_device_maps and k.index in curr_device_maps[to]:
                curr_v = super().device_maps[to][k.index]
                if curr_v != v.index:
                    raise ValueError(
                        "`set_device_map` only supports 1-to-1 mapping, "
                        f"trying to map {k} to {v} and {curr_v}"
                    )
            device_index_map[k.index] = v.index
        super().set_device_map(to, device_index_map)