55 lines
1.7 KiB
Python
55 lines
1.7 KiB
Python
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# Copyright 2019 Kakao Brain
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#
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# Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
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#
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# This source code is licensed under the BSD license found in the
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# LICENSE file in the root directory of this source tree.
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"""Arbitrary dependency between two autograd lanes."""
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from typing import List, Tuple
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import torch
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from torch import Tensor
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from .phony import get_phony
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__all__: List[str] = ["fork", "Fork", "join", "Join"]
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def fork(input: Tensor) -> Tuple[Tensor, Tensor]:
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"""Branches out from an autograd lane of the given tensor."""
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if torch.is_grad_enabled() and input.requires_grad:
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input, phony = Fork.apply(input)
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else:
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phony = get_phony(input.device, requires_grad=False)
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return input, phony
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class Fork(torch.autograd.Function):
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@staticmethod
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def forward(ctx: "Fork", input: Tensor) -> Tuple[Tensor, Tensor]: # type: ignore[override]
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phony = get_phony(input.device, requires_grad=False)
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return input.detach(), phony.detach()
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@staticmethod
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def backward(ctx: "Fork", grad_input: Tensor, grad_grad: Tensor) -> Tensor: # type: ignore[override]
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return grad_input
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def join(input: Tensor, phony: Tensor) -> Tensor:
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"""Merge two autograd lanes."""
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if torch.is_grad_enabled() and (input.requires_grad or phony.requires_grad):
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input = Join.apply(input, phony)
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return input
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class Join(torch.autograd.Function):
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@staticmethod
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def forward(ctx: "Join", input: Tensor, phony: Tensor) -> Tensor: # type: ignore[override]
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return input.detach()
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@staticmethod
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def backward(ctx: "Join", grad_input: Tensor) -> Tuple[Tensor, None]: # type: ignore[override]
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return grad_input, None
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