[3.14] gh-143650: Fix importlib race condition on import failure (GH-143651) #144662
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…onGH-143651) Fix a race condition where a thread could receive a partially-initialized module when another thread's import fails. The race occurs when: 1. Thread 1 starts importing, adds module to sys.modules 2. Thread 2 sees the module in sys.modules via the fast path 3. Thread 1's import fails, removes module from sys.modules 4. Thread 2 returns a stale module reference not in sys.modules The fix adds verification after the "skip lock" optimization in both Python and C code paths to check if the module is still in sys.modules. If the module was removed (due to import failure), we retry the import so the caller receives the actual exception from the import failure rather than a stale module reference. (cherry picked from commit ac8b5b6890006ee7254ea878866cb486ff835ecb) Co-authored-by: Gregory P. Smith <68491+gpshead@users.noreply.github.com> Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
miss-islington
requested review from
brettcannon,
ericsnowcurrently,
kumaraditya303,
ncoghlan and
warsaw
as code owners
This was referenced Feb 10, 2026
brettcannon
requested review from
gpshead
and removed request for
brettcannon
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Fix a race condition where a thread could receive a partially-initialized
module when another thread's import fails. The race occurs when:
The fix adds verification after the "skip lock" optimization in both Python
and C code paths to check if the module is still in sys.modules. If the
module was removed (due to import failure), we retry the import so the
caller receives the actual exception from the import failure rather than
a stale module reference.
(cherry picked from commit ac8b5b6)
Co-authored-by: Gregory P. Smith 68491+gpshead@users.noreply.github.com
Co-Authored-By: Claude Opus 4.5 noreply@anthropic.com