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import weakref
from typing import Any, Dict, Iterable, List, Optional, Set, Tuple
import torch
import torch.nn as nn
from torch.distributed._composable_state import _State
from torch.nn.parallel import DistributedDataParallel
from .contract import _get_registry, contract
_ROOT_MODULE_PREFIX = ""
class _ReplicateState(_State):
def __init__(self) -> None:
super().__init__()
self.module: nn.Module = nn.ParameterList()
self.has_initialized: bool = False
self._param_list: nn.ParameterList = nn.ParameterList()
# TODO(@fegin): this variable is originally create for testing, we
# should remove this if possible.
self._param_names: List[str] = []
def _collect_params(
self,
module: nn.Module,
ignored_modules: Set[nn.Module],
ignored_params: Set[nn.Parameter],
prefix: str = _ROOT_MODULE_PREFIX,
) -> None:
# skip if managed by fully_sharded API
if _is_fully_sharded(module):
return
# if a module is ignored, all descendants of the module are ignored.
if module in ignored_modules:
return
recurse_prefix = (
f"{prefix}." if prefix != _ROOT_MODULE_PREFIX else _ROOT_MODULE_PREFIX
)
for n, p in module.named_parameters(recurse=False):
if p not in ignored_params:
self._param_list.append(p)
self._param_names.append(f"{recurse_prefix}{n}")
for name, child_module in module.named_children():
self._collect_params(
child_module,
ignored_modules,
ignored_params,
prefix=f"{recurse_prefix}{name}",
)
def init(
self,
module: nn.Module,
ignored_modules: Set[nn.Module],
**kwargs,
) -> None:
if _is_fully_sharded(module):
raise RuntimeError(
"Cannot apply `replicate()` on a Module already managed by `fully_shard`"
)
if self.has_initialized:
return
self.has_initialized = True
self.module = module
ignored_params = {p for m in ignored_modules for p in m.parameters()}
self._collect_params(module, ignored_modules, ignored_params)
module.register_forward_pre_hook(self.forward_pre_hook, with_kwargs=True)
module.register_forward_hook(self.forward_post_hook) # type: ignore[arg-type]
if "device_id" in kwargs:
# replicate() supports a small usability enhancement where
# user can pass in device_id as a Union[int, torch.device] even for
# CPU devices so users don't have to change code for CPU/GPU runs.
# We derive the right device_ids to feed into DDP to support this.
if kwargs["device_id"] is not None:
device_id = kwargs["device_id"]
# Convert to device_ids that DDP expects.
if isinstance(device_id, torch.device) and device_id.type == "cpu":
# CPU modules receive device_ids None
kwargs["device_ids"] = None
else:
# GPU modules expect device_ids=[cuda_device]
kwargs["device_ids"] = [device_id]
else:
kwargs["device_ids"] = None
kwargs.pop("device_id")
self._ddp = DistributedDataParallel(self._param_list, **kwargs)
# Weakref to the DDP instance is currently only used for testing.
replicate.state(self.module)._ddp_weakref = weakref.ref(self._ddp)
def forward_pre_hook(
self, module: nn.Module, args: Tuple[Any, ...], kwargs: Dict[str, Any]
) -> Any:
return self._ddp._pre_forward(*args, **kwargs)
def forward_post_hook(
self,
module: nn.Module,
input: Tuple[torch.Tensor],
output: torch.Tensor,
) -> torch.Tensor:
return self._ddp._post_forward(output)
@contract(state_cls=_ReplicateState)
def replicate(
module: nn.Module,
ignored_modules: Optional[Iterable[torch.nn.Module]] = None,
**kwargs,
) -> nn.Module:
r"""Replicates a module
Args:
module (torch.nn.Module): module to replicate
Example::
>>> # xdoctest: +REQUIRES(module:torch._C._distributed_c10d)
>>> module = nn.Linear(3, 3)
>>> replicate(module)
"""
torch._C._log_api_usage_once("torch.distributed.replicate")
# TODO(fegin): using kwargs is not a good idea if we would like to make
# replicate a formal API to replace DDP.
if "device_id" in kwargs:
if not isinstance(kwargs["device_id"], (int, torch.device)):
raise RuntimeError(
"Expected device_id to be int or torch.device, "
f"but got {type(kwargs['device_id'])}"
)
if ignored_modules is None:
ignored_modules = {}
else:
ignored_modules = set(ignored_modules)
replicate.state(module).init(module, ignored_modules, **kwargs)
return module
def _is_fully_sharded(module: nn.Module) -> bool:
r"""Check if module is marked with fully_shard."""
registry = _get_registry(module)
if registry is None:
return False
return "fully_shard" in registry