🐛 fix(windows): stop leaking memory on repeated folder lookups#507
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gaborbernat merged 2 commits intoJul 15, 2026
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get_win_folder_via_ctypes defined a fresh _GUID Structure on every call. Each POINTER(_GUID) registered a new entry in ctypes._pointer_type_cache that was never released, so repeated calls leaked memory unboundedly. Build the _GUID class and DLL bindings once via functools.cache and reuse the resolver across calls. Fixes tox-dev#501
get_win_folder_from_registry left the opened key handle to be reclaimed by the garbage collector. Under frequent calls that relies on GC timing to release OS handles; use a context manager so the handle closes deterministically.
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Looking up a Windows folder path in a loop leaked memory. A service that builds a cache path with
platformdirs.user_data_pathabout once a second grew by gigabytes of retained RAM over a few hours, as issue #501 reports. 🐛 Each call toget_win_folder_via_ctypesdefined a new_GUIDStructuresubclass, and everyPOINTER(_GUID)registered an entry inctypes._pointer_type_cachethat nothing released.The change builds the
_GUIDclass and the three DLL bindings once behindfunctools.cacheand runs a resolver closure over them on each call.get_win_folder_via_ctypeskeeps its signature and delegates to the cached builder, so the fallback selector and every caller stay the same. A second commit closes the registry-fallback key with a context manager rather than leaving the OS handle for the garbage collector to reclaim.I confirmed the fix by exercising the real function 10,000 times, stubbing only
WinDLLandsys.platformsoPOINTERandStructurestill run. On Python 3.13 the cache and the retained_GUIDclasses stop growing, and memray reports a large drop in peak memory. ✨ctypes._pointer_type_cache_GUIDclassesPython 3.14 already reworked
_pointer_type_cacheupstream, which hides the cache symptom on that version, while the retained-object growth it fixes is version-independent. Returned paths are unchanged.