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GeezerVison is showing github.com — bpo-46771: Remove two controversial lines from Task.cancel() by gvanrossum · Pull Request #31623 · python/cpython

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@gvanrossum

@gvanrossum gvanrossum commented Feb 28, 2022 •
edited by bedevere-bot
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Also from the _asyncio C accelerator module,
and adjust one test that the change caused to fail.

For more discussion see the discussion starting here:
#31394 (comment)

(Basically, @asvetlov proposed to return False from cancel()
when there is already a pending cancellation, and I went along,
even though it wasn't necessary for the task group implementation,
and @agronholm has come up with a counterexample that fails
because of this change. So now I'm changing it back to the old
semantics (but still bumping the counter) until we can have a
proper discussion about this.)

https://bugs.python.org/issue46771

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@gvanrossum
Remove two controversial lines from Task.cancel()
0feaade 
Also from the _asyncio C accelerator module,
and adjust one test that the change caused to fail.

For more discussion see the discussion starting here:
#31394 (comment)

(Basically, @asvetlov proposed to return False from cancel()
when there is already a pending cancellation, and I went along,
even though it wasn't necessary for the task group implementation,
and @agronholm has come up with a counterexample that fails
because of this change.  So now I'm changing it back to the old
semantics (but still bumping the counter) until we can have a
proper discussion about this.)
@gvanrossum
gvanrossum requested review from 1st1 and asvetlov as code owners February 28, 2022 20:21
@bedevere-bot bedevere-bot added the awaiting core review label Feb 28, 2022
@the-knights-who-say-ni the-knights-who-say-ni added the CLA signed label Feb 28, 2022
@gvanrossum gvanrossum added the skip news label Feb 28, 2022
@gvanrossum gvanrossum mentioned this pull request Feb 28, 2022
bpo-46771: Implement asyncio context managers for handling timeouts #31394
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@agronholm

agronholm commented Feb 28, 2022

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This seems like a step in the right direction, but further changes will be necessary.
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@gvanrossum

gvanrossum commented Feb 28, 2022

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This seems like a step in the right direction, but further changes will be necessary.

Could you be more specific? What use case are you thinking of?
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asvetlov
asvetlov approved these changes Feb 28, 2022
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I'm fine with this.
.uncancel() makes the change not necessary.
Deprecation of cancellation message clears my other objections.
Sorry, I'm not active this week. Hard events in my life :(

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@bedevere-bot bedevere-bot added awaiting merge and removed awaiting core review labels Feb 28, 2022
@agronholm

agronholm commented Feb 28, 2022

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This seems like a step in the right direction, but further changes will be necessary.

Could you be more specific? What use case are you thinking of?

Unless more changes are made, old-style cancel scope-like context managers will distort the cancel counter. It should be reset to 0 when the task is made cancellable again (when the CancelledError has been delivered to the task). This should improve the interaction of counter-aware context managers and non-aware ones by letting the aware ones function correctly in the case of a re-cancellation when the aware context manager is the outer one and the non-aware one is the inner one.
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@agronholm

agronholm commented Feb 28, 2022

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Ideally I would have liked the CancelledError to carry this information. That would make it easier to write code compatible with 3.9 - 3.10 since those versions will have to use the cancel message trick.
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@gvanrossum
gvanrossum merged commit 7d611b4 into main Feb 28, 2022
@gvanrossum
gvanrossum deleted the change-cancel branch February 28, 2022 23:15
@bedevere-bot bedevere-bot removed the awaiting merge label Feb 28, 2022
@gvanrossum

gvanrossum commented Feb 28, 2022

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@agronholm Would you mind submitting a (draft) PR? I personally think that if we have a solution that will work great in the future, making the existing cancel scope implementations have to do a version check would be a small price to pay.
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@Tinche

Tinche commented Mar 1, 2022

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Could you also tag me in that PR? Trying to wrap my head around the issue.
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@agronholm

agronholm commented Mar 1, 2022

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I'm currently on a work trip but will try work on that in the next few days.
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@gvanrossum gvanrossum mentioned this pull request May 24, 2022
Implement asyncio.timeout() context manager #90927
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@asvetlov asvetlov asvetlov approved these changes
@1st1 1st1 Awaiting requested review from 1st1 1st1 is a code owner

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6 participants

@gvanrossum @agronholm @Tinche @asvetlov @the-knights-who-say-ni @bedevere-bot
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