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GeezerVison is showing github.com — gh-159739: Skip context watchers cleared during notification by jelle-openai · Pull Request #160164 · python/cpython

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@jelle-openai

@jelle-openai jelle-openai commented Oct 22, 2026 •
edited by bedevere-app Bot
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A context watcher callback can clear a later watcher while a context-switch notification is being dispatched. The dispatcher still uses its earlier snapshot of active watchers, so it calls a NULL callback and crashes; check that each callback is still registered before invoking it. Backport to 3.15 and 3.14.

  • Issue: Fix minor safety issues #159739

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@jelle-openai
pythongh-159739: Skip context watchers cleared during notification
b70cca5 
A context watcher callback can clear a later watcher while a context-switch notification is being dispatched. The dispatcher still uses its earlier snapshot of active watchers, so it calls a NULL callback and crashes; check that each callback is still registered before invoking it. Backport to 3.15 and 3.14.
@jelle-openai
jelle-openai requested a review from 1st1 as a code owner October 22, 2026 03:45
@bedevere-app bedevere-app Bot added the awaiting review label Oct 22, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 22, 2026
Fix minor safety issues #159739
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@JelleZijlstra
JelleZijlstra merged commit 0a57626 into python:main Oct 22, 2026
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@bedevere-app bedevere-app Bot removed the awaiting review label Oct 22, 2026
@JelleZijlstra JelleZijlstra added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 22, 2026
@miss-islington-app

miss-islington-app Bot commented Oct 22, 2026

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Thanks @jelle-openai for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖
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@miss-islington-app

miss-islington-app Bot commented Oct 22, 2026

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Thanks @jelle-openai for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖
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@bedevere-app

bedevere-app Bot commented Oct 22, 2026

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GH-160289 is a backport of this pull request to the 3.14 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Oct 22, 2026
@bedevere-app

bedevere-app Bot commented Oct 22, 2026

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GH-160291 is a backport of this pull request to the 3.15 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Oct 22, 2026
JelleZijlstra pushed a commit that referenced this pull request Oct 22, 2026
@miss-islington @jelle-openai
[3.15] gh-159739: Skip context watchers cleared during notification (G…
9986943 
…H-160164) (#160291)

A context watcher callback can clear a later watcher while a context-switch notification is being dispatched. The dispatcher still uses its earlier snapshot of active watchers, so it calls a NULL callback and crashes; check that each callback is still registered before invoking it. Backport to 3.15 and 3.14.
(cherry picked from commit 0a57626)

Co-authored-by: Jelle Zijlstra <[email protected]>
JelleZijlstra pushed a commit that referenced this pull request Oct 22, 2026
@miss-islington @jelle-openai
[3.14] gh-159739: Skip context watchers cleared during notification (G…
ddf7156 
…H-160164) (#160289)

A context watcher callback can clear a later watcher while a context-switch notification is being dispatched. The dispatcher still uses its earlier snapshot of active watchers, so it calls a NULL callback and crashes; check that each callback is still registered before invoking it. Backport to 3.15 and 3.14.
(cherry picked from commit 0a57626)

Co-authored-by: Jelle Zijlstra <[email protected]>
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@jelle-openai @JelleZijlstra
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