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gh-103758: Add test for multiple os.register_at_fork registrations - #159705

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plfj wants to merge 1 commit into

python:mainfrom

plfj:gh-103758-fork-order

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gh-103758: Add test for multiple os.register_at_fork registrations#159705
plfj wants to merge 1 commit into
python:mainfrom
plfj:gh-103758-fork-order

plfj commented Oct 19, 2026

Fixes gh-103758.
Supersedes and closes gh-103759.

Summary

Adds a regression test in Lib/test/test_os/test_posix.py to verify that registering callbacks multiple times via os.register_at_fork() correctly preserves both old and newly registered handlers across successive forks.

Specifically, it verifies:

before handlers execute in LIFO (reverse) order.
after_in_parent handlers execute in FIFO order.
after_in_child handlers execute in FIFO order.
Handlers registered after an earlier fork accumulate and run alongside previous generations in subsequent forks.

Note on Previous Work

This issue was originally reported by @itsankitkp with an initial implementation in #103759.

This PR supersedes #103759 by addressing reliability issues in the earlier attempt:

Eliminates multi-process race conditions on a shared pipe by validating events per-process in memory.
Eliminates pipe token-starvation deadlocks on child exit.
Uses test.support.wait_process to reap child processes cleanly and verify exit status.

Credit is attributed to the original author via the commit trailer (Co-authored-by).

Checklist

Tested locally with ./python -m test -v test_os.test_posix
All required CI checks passed cleanly
No NEWS entry required (test-only change as per Devguide)

python-cla-bot Bot commented Oct 19, 2026 •

edited

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bedevere-app Bot added the type-feature label

bedevere-app Bot mentioned this pull request

Add test case in os.register_at_fork to verify new and old forkers get executed #103758

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bedevere-app Bot added awaiting review tests labels

bedevere-app Bot commented Oct 19, 2026

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

plfj force-pushed the gh-103758-fork-order branch from 5e815cc to 6f97f0a Compare

October 19, 2026 15:30

bedevere-app Bot commented Oct 19, 2026

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

plfj force-pushed the gh-103758-fork-order branch from 6f97f0a to df98a97 Compare

October 20, 2026 10:35

bedevere-app Bot commented Oct 20, 2026

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

plfj force-pushed the gh-103758-fork-order branch 3 times, most recently from c9d2617 to a7dd836 Compare

October 20, 2026 16:20

bedevere-app Bot commented Oct 20, 2026

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.


          pythongh-103758: Test that os.register_at_fork handlers accumulate ac…

e177458

…ross forks

Add a test verifying that handlers registered after an earlier fork()
run together with previously registered handlers in subsequent forks,
preserving LIFO order for 'before' handlers and FIFO order for 'after_*'
handlers.

Co-authored-by: Ankit Kumar Pandey <[email protected]>

plfj force-pushed the gh-103758-fork-order branch from a7dd836 to e177458 Compare

October 24, 2026 17:10

bedevere-app Bot commented Oct 24, 2026

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

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awaiting review tests type-feature