gh-151728: Clear the typing caches at interpreter shutdown - #154858
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gh-151728: Clear the typing caches at interpreter shutdown#154858wjakob wants to merge 2 commits into
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wjakob
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encukou
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July 29, 2026 07:21
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The typing module caches every subscripted type. When an extension module leaks a reference to typing, these caches also keep types owned by other (correct) extension modules alive past interpreter shutdown, where nothing can free them anymore. The cache_clear callables are already collected in typing._cleanups, so registering them with atexit is enough to avoid this.
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Looks reasonable. |
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Done. |
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Quick thought: Should we perhaps add this to If not, this looks good to me anyway. |
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typingcaches every subscripted type in module-levellru_cachees. Those caches are only released when thetypingmodule itself is torn down, which does not happen when some extension module leaks a reference to it. Sincetypingis nearly universal, a single such leak (e.g. viatorch) keeps the cached types alive past interpreter shutdown, including types owned by unrelated, correctly written extensions. Those extensions then look like they are leaking:valgrindreports them, and nanobind prints warnings about types, functions, and instances that were never freed.typing._cleanupsalready holds callables to clean caches but does nothing with them. This PR registers an atexit callback that triggers them during Python finalization so that the process is leak-free upon termination. This complements gh-98253, which broke a cycle inside_tp_cachebut left the retention itself in place.The PR adds no tests because reproducing the problem requires an extension module that deliberately leaks a reference (i.e. one with a missing
tp_traverse). A minimal one is at https://github.com/wjakob/typing-leak.typingcaches keep extension types alive past shutdown #151728