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GeezerVison is showing github.com — gh-153020: Fix race condition on event_tstate in _tkinter by tangyuan0821 · Pull Request #153640 · python/cpython

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@tangyuan0821

@tangyuan0821 tangyuan0821 commented Jul 13, 2026 •
edited by bedevere-app Bot
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event_tstate in Modules/_tkinter.c is read by the EventHook thread and
written by the main thread, so they race. I load and store it with atomic
ops, and clear it to NULL in DisableEventHook before the PyThreadState is
released.

  • Issue: Data race on event_tstate in _tkinter.c under free-threading #153020

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@bedevere-app bedevere-app Bot mentioned this pull request Jul 13, 2026
Data race on event_tstate in _tkinter.c under free-threading #153020
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@bedevere-app bedevere-app Bot added the awaiting review label Jul 13, 2026
IvyXu420
IvyXu420 reviewed Jul 13, 2026
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If the race is only possible in FT, why not use macros like FT_ATOMIC_LOAD_PTR or FT_ATOMIC_STORE_PTR to avoid the potential performance overhead in the default build?

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tangyuan0821 added 2 commits July 13, 2026 16:15
@tangyuan0821
pythongh-153020: Fix race condition on event_tstate in _tkinter
4c998f3
@tangyuan0821
pythongh-153020: Add NEWS entry for _tkinter data race fix
00a72c2
@tangyuan0821
tangyuan0821 force-pushed the 153020 branch from 6e7c0ef to 00a72c2 Compare July 13, 2026 08:20
@tangyuan0821

tangyuan0821 commented Jul 13, 2026

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If the race is only possible in FT, why not use macros like FT_ATOMIC_LOAD_PTR or FT_ATOMIC_STORE_PTR to avoid the potential performance overhead in the default build?

Good catch, switched to FT_ATOMIC_* since the race is only under free-threading. The default build just reads and writes it directly.
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IvyXu420
IvyXu420 reviewed Jul 18, 2026
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The suffix of the news entry filename looks incorrect. It should be a nonce generated by blurb, see https://devguide.python.org/getting-started/pull-request-lifecycle/#how-to-add-a-news-entry.

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Comment thread Misc/NEWS.d/next/Library/2026-07-13-10-37-32.gh-issue-153020.eventTs.rst Resolved

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Update Misc/NEWS.d/next/Library/2026-07-13-10-37-32.gh-issue-153020.e…
ee1ffef 
…ventTs.rst

Co-authored-by: Ivy Xu <[email protected]>
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github-actions Bot commented Oct 28, 2026

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This PR is stale because it has been open for 90 days with no activity.
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@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label Oct 28, 2026
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@tangyuan0821 @IvyXu420
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