Source code for torch.distributed.pipeline.sync.skip.skippable
# Copyright 2019 Kakao Brain
#
# Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
#
# This source code is licensed under the BSD license found in the
# LICENSE file in the root directory of this source tree.
"""The user interface to define skip connections."""
from typing import (
TYPE_CHECKING,
Any,
Callable,
ClassVar,
Dict,
FrozenSet,
Generator,
Iterable,
List,
Optional,
Set,
Sequence,
Tuple,
Type,
TypeVar,
Union,
cast,
)
from torch import Tensor, nn
from ..microbatch import Batch
from .namespace import Namespace
from .tracker import current_skip_tracker
__all__ = ["skippable", "stash", "pop", "verify_skippables"]
Tensors = Sequence[Tensor]
TensorOrTensors = Union[Tensor, Tensors]
StashPop = Union["stash", "pop"]
StashPopGenerator = Generator[StashPop, Optional[Tensor], TensorOrTensors]
if TYPE_CHECKING:
# Typechecking: nn.Module is not a Generic
SkippableModule = nn.Module[Union[StashPopGenerator, TensorOrTensors]] # type: ignore[type-arg]
else:
SkippableModule = nn.Module
T = TypeVar("T", bound="Skippable")
class Skippable(nn.Module):
"""The base class for skippable modules.
Do not use this class directly. Define a subclass by :func:`skippable`
instead.
"""
module_cls: ClassVar[Type[SkippableModule]]
stashable_names: ClassVar[FrozenSet[str]]
poppable_names: ClassVar[FrozenSet[str]]
def __init__(self, *args: Any, **kwargs: Any) -> None:
super().__init__()
self.module = self.module_cls(*args, **kwargs) # type: ignore[call-arg]
self.namespaces: Dict[str, Namespace] = {}
def __repr__(self) -> str:
return f"@skippable({self.module})"
def namespaced(self, name: str) -> Tuple[Namespace, str]:
"""Prepend namespace for the given skip name."""
ns = self.namespaces.get(name)
ns = cast(Namespace, ns)
return (ns, name)
def stashable(self) -> Iterable[Tuple[Namespace, str]]:
"""Iterate over namespaced skip names to be stashed."""
for name in self.stashable_names:
yield self.namespaced(name)
def poppable(self) -> Iterable[Tuple[Namespace, str]]:
"""Iterate over namespaced skip names to be popped."""
for name in self.poppable_names:
yield self.namespaced(name)
def isolate(self: T, ns: Namespace, *, only: Optional[Iterable[str]] = None) -> T:
r"""Isolate a specified subset or the whole set of skip tensors.
In a single sequential module, skip tensors with the same
name are not allowed unless they are isolated by different namespaces.
Here's an example using the same name for skip tensors twice. Each pair
of ``Layer1`` and ``Layer2`` is isolated with its own namespace ``ns1``
and ``ns2``. There is no conflict anymore::
ns1 = Namespace()
ns2 = Namespace()
model = nn.Sequential(
Layer1().isolate(ns1),
Layer1().isolate(ns2),
Layer2(),
Layer3().isolate(ns2),
Layer3().isolate(ns1),
)
When `only` parameter is omitted, all skip tensors are isolated. You
can isolate a subset of skip tensors by passing `only` parameter::
ns_alice = Namespace()
ns_bob = Namespace()
model = nn.Sequential(
...
StashStashPop().isolate(ns_alice, only=['alice']) \
.isolate(ns_bob, only=['bob']),
...
)
Args:
ns (Namespace):
namespace for isolation
Keyword Args:
only (iterable of strs):
names of specific skip tensors to be isolated (omit this option
to isolate all skip tensors declared in this module)
Returns:
this module itself
"""
names: Iterable[str]
if only is None:
names = self.stashable_names | self.poppable_names
else:
names = set(only)
for name in names:
self.namespaces[name] = ns
return self
def dispatch(
self,
input,
handle_stash: Callable[[str, Optional[Tensor]], None],
handle_pop: Callable[[str], Optional[Tensor]],
):
"""Dispatch :class:`stash` or :class:`pop` commands.
The commands are generated by the module's ``forward()``.
"""
generator = self.module(input)
if not isinstance(generator, Generator):
# The underlying module returned output without any yield.
output = generator
return output
try:
op = next(generator)
while True:
if isinstance(op, stash):
handle_stash(op.name, op.tensor)
op = next(generator)
continue
if isinstance(op, pop):
tensor = handle_pop(op.name)
op = generator.send(tensor)
continue
raise TypeError(f"{op!r} is not a command from @skippable")
except StopIteration as stop:
output = stop.args[0]
return output
def forward(self, input: Union[List[Any], Tensor]) -> TensorOrTensors:
"""Perform the forward propagation.
:class:`stash` or :class:`pop` commands will be handled by portals
silently. The portals won't be exposed to users.
Raises:
RuntimeError:
illegal 'stash' or 'pop' is found.
"""
skip_tracker = current_skip_tracker()
stashed_tensors: Dict[str, Optional[Tensor]] = {}
# Load skip tensors that might be popped.
poppable_tensors = {}
batch = Batch(input)
for ns, name in self.poppable():
try:
poppable_tensors[name] = skip_tracker.load(batch, ns, name)
except KeyError as e:
raise RuntimeError(f"'{name}' has not been stashed") from e
input = batch.values
# Handle skip commands.
def handle_stash(name: str, tensor: Optional[Tensor]) -> None:
if name not in self.stashable_names:
raise RuntimeError(f"'{name}' has not been declared as stashable")
stashed_tensors[name] = tensor
def handle_pop(name: str) -> Optional[Tensor]:
if name not in self.poppable_names:
raise RuntimeError(f"'{name}' has not been declared as poppable")
return poppable_tensors.pop(name)
output = self.dispatch(input, handle_stash, handle_pop)
# All declared skips must be stashed or popped.
not_stashed = self.stashable_names - stashed_tensors.keys()
if not_stashed:
comma_names = ", ".join(f"'{n}'" for n in not_stashed)
raise RuntimeError(f"{comma_names} must be stashed but have not")
not_popped = poppable_tensors.keys()
if not_popped:
comma_names = ", ".join(f"'{n}'" for n in not_popped)
raise RuntimeError(f"{comma_names} must be popped but have not")
# Save stashed skip tensors.
batch = Batch(output)
for ns, name in self.stashable():
tensor = stashed_tensors[name]
skip_tracker.save(batch, ns, name, tensor)
output = batch.values
return output
# TODO(sublee): Move to above of Skippable class for better read flow.
[docs]def skippable(
stash: Iterable[str] = (), pop: Iterable[str] = (),
) -> Callable[[Type[SkippableModule]], Type[Skippable]]:
"""Define a decorator to create :class:`nn.Module <torch.nn.Module>` with skip connections.
These decorated modules are called "skippable". This functionality works perfectly
fine even when the module is not wrapped by :class:`~torch.distributed.pipeline.sync.Pipe`.
Each skip tensor is managed by its name. Before manipulating skip tensors,
a skippable module must statically declare the names for skip tensors by
`stash` and/or `pop` parameters. Skip tensors with pre-declared name can be
stashed by ``yield stash(name, tensor)`` or popped by ``tensor = yield
pop(name)``.
Here is an example with three layers. A skip tensor named "1to3" is stashed
and popped at the first and last layer, respectively::
@skippable(stash=['1to3'])
class Layer1(nn.Module):
def forward(self, input):
yield stash('1to3', input)
return f1(input)
class Layer2(nn.Module):
def forward(self, input):
return f2(input)
@skippable(pop=['1to3'])
class Layer3(nn.Module):
def forward(self, input):
skip_1to3 = yield pop('1to3')
return f3(input) + skip_1to3
model = nn.Sequential(Layer1(), Layer2(), Layer3())
One skippable module can stash or pop multiple skip tensors::
@skippable(stash=['alice', 'bob'], pop=['carol'])
class StashStashPop(nn.Module):
def forward(self, input):
yield stash('alice', f_alice(input))
yield stash('bob', f_bob(input))
carol = yield pop('carol')
return input + carol
Every skip tensor must be associated with exactly one pair of `stash` and
`pop`. :class:`~torch.distributed.pipeline.sync.Pipe` checks this
restriction automatically when wrapping a module. You can also check the
restriction by :func:`verify_skippables`
without :class:`~torch.distributed.pipeline.sync.Pipe`.
"""
stashable_names = frozenset(stash)
poppable_names = frozenset(pop)
def extend_skippable(module_cls: Type[SkippableModule]) -> Type[Skippable]:
name = module_cls.__name__
bases = (Skippable,)
attrs = {"module_cls": module_cls, "stashable_names": stashable_names, "poppable_names": poppable_names}
return type(name, bases, attrs)
return extend_skippable
[docs]class stash:
"""The command to stash a skip tensor.
::
def forward(self, input):
yield stash('name', input)
return f(input)
Args:
name (str): name of skip tensor
input (torch.Tensor or None): tensor to pass to the skip connection
"""
__slots__ = ("name", "tensor")
def __init__(self, name: str, tensor: Optional[Tensor]) -> None:
self.name = name
self.tensor = tensor
[docs]class pop:
"""The command to pop a skip tensor.
::
def forward(self, input):
skip = yield pop('name')
return f(input) + skip
Args:
name (str): name of skip tensor
Returns:
the skip tensor previously stashed by another layer under the same name
"""
__slots__ = ("name",)
def __init__(self, name: str) -> None:
self.name = name
[docs]def verify_skippables(module: nn.Sequential) -> None:
"""Verify if the underlying skippable modules satisfy integrity.
Every skip tensor must have only one pair of `stash` and `pop`. If there
are one or more unmatched pairs, it will raise :exc:`TypeError` with the
detailed messages.
Here are a few failure cases. :func:`verify_skippables` will report failure
for these cases::
# Layer1 stashes "1to3".
# Layer3 pops "1to3".
nn.Sequential(Layer1(), Layer2())
# └──── ?
nn.Sequential(Layer2(), Layer3())
# ? ────┘
nn.Sequential(Layer1(), Layer2(), Layer3(), Layer3())
# └───────────────────┘ ^^^^^^
nn.Sequential(Layer1(), Layer1(), Layer2(), Layer3())
# ^^^^^^ └───────────────────┘
To use the same name for multiple skip tensors, they must be isolated by
different namespaces. See :meth:`isolate()
<torchpipe.skip.skippable.Skippable.isolate>`.
Raises:
TypeError:
one or more pairs of `stash` and `pop` are not matched.
"""
stashed: Set[Tuple[Namespace, str]] = set()
popped: Set[Tuple[Namespace, str]] = set()
msgs: List[str] = []
for layer_name, layer in module.named_children():
if not isinstance(layer, Skippable):
continue
for name in layer.stashable_names & layer.poppable_names:
msg = f"'{layer_name}' declared '{name}' both as stashable and as poppable"
msgs.append(msg)
for ns, name in layer.stashable():
if name in layer.poppable_names:
continue
if (ns, name) in stashed:
msg = f"'{layer_name}' redeclared '{name}' as stashable but not isolated by namespace"
msgs.append(msg)
continue
stashed.add((ns, name))
for ns, name in layer.poppable():
if name in layer.stashable_names:
continue
if (ns, name) in popped:
msg = f"'{layer_name}' redeclared '{name}' as poppable but not isolated by namespace"
msgs.append(msg)
continue
if (ns, name) not in stashed:
msg = f"'{layer_name}' declared '{name}' as poppable but it was not stashed"
msgs.append(msg)
continue
popped.add((ns, name))
for (_, name) in stashed - popped:
msg = f"no module declared '{name}' as poppable but stashed"
msgs.append(msg)
if msgs:
raise TypeError(
"one or more pairs of stash and pop do not match:\n\n%s" "" % "\n".join("* %s" % x for x in msgs)
)
