8000 gh-94972: document that shield users need to keep a reference to their task by hendrikmakait · Pull Request #96724 · python/cpython · GitHub
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gh-94972: document that shield users need to keep a reference to their task #96724

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Merged
merged 7 commits into from
Sep 10, 2022
Merged

gh-94972: document that shield users need to keep a reference to their task #96724

merged 7 commits into from
Sep 10, 2022

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hendrikmakait
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@hendrikmakait hendrikmakait commented Sep 9, 2022 •
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I will take over the original PR (#94973) from @graingert to get it over the finish line.

@bedevere-bot bedevere-bot added awaiting review docs Documentation in the Doc dir skip news labels Sep 9, 2022
@hendrikmakait hendrikmakait mentioned this pull request Sep 9, 2022
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ghost commented Sep 9, 2022 •
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gvanrossum
gvanrossum approved these changes Sep 9, 2022
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Thanks for finishing this! I'll merge now.

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Oh wait, it's still in draft. I'll leave it up to you to remove draft mode; ping the PR and I'll merge it then.

@hendrikmakait hendrikmakait marked this pull request as ready for review September 10, 2022 06:54
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@gvanrossum: Moved out of draft, thanks for the early review.

@gvanrossum gvanrossum merged commit 6281aff into python:main Sep 10, 2022
@gvanrossum gvanrossum added needs backport to 3.10 only security fixes needs backport to 3.11 only security fixes labels Sep 10, 2022
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Thanks @hendrikmakait for the PR, and @gvanrossum for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

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Thanks @hendrikmakait for the PR, and @gvanrossum for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

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GH-96736 is a backport of this pull request to the 3.10 branch.

@bedevere-bot bedevere-bot removed the needs backport to 3.10 only security fixes label Sep 10, 2022
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GH-96737 is a backport of this pull request to the 3.11 branch.

@bedevere-bot bedevere-bot removed the needs backport to 3.11 only security fixes label Sep 10, 2022
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Sep 10, 2022
@hendrikmakait @miss-islington
pythongh-94972: document that shield users need to keep a reference t…
e2f7c8c 
…o their task (pythonGH-96724)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
(cherry picked from commit 6281aff)

Co-authored-by: Hendrik Makait <hendrik.makait@gmail.com>
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Sep 10, 2022
@hendrikmakait @miss-islington
pythongh-94972: document that shield users need to keep a reference t…
13de3da 
…o their task (pythonGH-96724)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
(cherry picked from commit 6281aff)

Co-authored-by: Hendrik Makait <hendrik.makait@gmail.com>
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Thanks Hendrik for finishing this up!

Thomas I hope you’re doing okay.

miss-islington added a commit that referenced this pull request Sep 10, 2022
@miss-islington @hendrikmakait
gh-94972: document that shield users need to keep a reference to thei…
9b71058 
…r task (GH-96724)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
(cherry picked from commit 6281aff)

Co-authored-by: Hendrik Makait <hendrik.makait@gmail.com>
miss-islington added a commit that referenced this pull request Sep 10, 2022
@miss-islington @hendrikmakait
gh-94972: document that shield users need to keep a reference to thei…
335bd1e 
…r task (GH-96724)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
(cherry picked from commit 6281
8000
aff)

Co-authored-by: Hendrik Makait <hendrik.makait@gmail.com>
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Sorry that I'm bringing this up so late. But, is this actually needed?

It seems to me that shield() has a reference to the task, so this should not be needed (i.e. It returns outer, which has a reference to _outer_done_callback, which has a reference to inner in the enclosing scope, which is the task. As long as you have a reference to outer (i.e. by awaiting it), I don't think inner can be garbage collected).

If I'm wrong about that somewhere, shouldn't we just fix shield() to keep a reference, rather than asking the user to make this extra, non-obvious step every time they use it?

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@Dreamsorcerer when the result of shield is cancelled the reference to the original task is dropped

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Ah, yes, fair enough. Still feels like an explicit reference could be kept on outer to avoid this though.

But, with the proposed workaround, wouldn't the function that holds the task reference also likely be dropped (i.e. If the CancelledError bubbles up, the entire function scope will be discarded shortly thereafter)?
Seems like you'd need to put the reference somewhere globally or as an attribute.

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@graingert graingert graingert approved these changes

@gvanrossum gvanrossum 72BD gvanrossum approved these changes

@1st1 1st1 Awaiting requested review from 1st1 1st1 is a code owner

@asvetlov asvetlov Awaiting requested review from asvetlov asvetlov is a code owner

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