Lightning-AI / Lightning-AI/lightning-thunder

Support `torch.Tensor.register_hook`

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Dominant language
Python
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Description

🚀 Feature

Motivation

In Lightning Fabric, we use this once for error checking that the user properly called backward. https://github.com/Lightning-AI/pytorch-lightning/blob/096b063d6eeb41567409f4a6b9bac6f5af28ed93/src/lightning/fabric/wrappers.py#L232-L233. cc @awaelchli

I don't expect that we run this hook properly on backward, but it would be useful to simply ignore it and not fail on it, maybe showing a warning.

Pitch
import thunder
import torch

def hook(_):
    print("Hello")

def fn(x):
    y = x * 2
    y.register_hook(hook)
    return y

t = torch.tensor([1.0], requires_grad=True)
fn = thunder.jit(fn)
out = fn(t)
out.backward()
print(out)
    y.register_hook(hook)
  File "/home/carmocca/git/lightning-thunder/thunder/core/interpreter.py", line 5862, in _impl
    return fn.__func__(fn.__self__, *args, **kwargs)
  File "/home/carmocca/git/lightning-thunder/thunder/core/interpreter.py", line 1243, in jit_wrapped
    res = ufn(*uargs, **ukwargs)
  File "/home/carmocca/git/lightning-thunder/thunder/core/proxies.py", line 1210, in __getattr__
    method: None | Callable = resolve_method(attr, self)
  File "/home/carmocca/git/lightning-thunder/thunder/core/langctxs.py", line 68, in resolve_method
    method: Callable = ctx.get_method(id, *args, **kwargs)
  File "/home/carmocca/git/lightning-thunder/thunder/torch/langctx.py", line 40, in get_method
    raise AttributeError(f"The {self.name} language context has no method {id}")
AttributeError: The torch language context has no method register_hook
Additional context

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the issue with the Lightning Fabric example and trace the method lookup through thunder/core/proxies.py and thunder/torch/langctx.py, especially get_method. Confirm how torch.Tensor.register_hook should be handled when compiled, then verify the example no longer fails and produces the intended ignored-hook or warning behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
python, pytorch
Domain
machine-learning
Issue type
Feature
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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