gh-129139: Fix setstate on exhausted list iterators in free-threaded build#146269

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ytang928 wants to merge 2 commits intopython:mainfrom

ytang928:gh-129139-fix-listiter-setstate

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gh-129139: Fix setstate on exhausted list iterators in free-threaded build#146269
ytang928 wants to merge 2 commits intopython:mainfrom
ytang928:gh-129139-fix-listiter-setstate

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ytang928 commentedMar 22, 2026

In free-threaded builds, exhausted list iterators signal exhaustion by
settingit_index to-1 without clearingit_seq toNULL (to avoid
expensive atomic refcount operations on the hot path). The existing
it_seq != NULL guard inlistiter_setstate andlistreviter_setstate
allowed__setstate__ to revive an exhausted iterator by resetting
it_index to a valid value.

This adds anit_index >= 0 check so that__setstate__ is a no-op on
exhausted iterators, consistent with GIL-enabled build behavior.

The same fix is applied to bothlistiter_setstate andlistreviter_setstate,
which share the same pattern.

Issue:list iterator__setstate__() differs for exhausted iterator GIL vs. non-GIL #129139

pythongh-129139: Fix __setstate__ on exhausted list iterators in free…

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…-threaded buildIn free-threaded builds, exhausted list iterators signal exhaustion bysetting it_index to -1 without clearing it_seq to NULL. The existingit_seq != NULL guard in listiter_setstate and listreviter_setstateallowed __setstate__ to revive an exhausted iterator by resettingit_index to a valid value.Add an it_index >= 0 check so that __setstate__ is a no-op onexhausted iterators, consistent with GIL-enabled build behavior.