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bpo-30891: Fix importlib _find_and_load() race condition #2646
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My patch changes how the global import lock is handled in _find_and_load(). Before my change, it was held for the whole function (to simplify). With my change, it is now acquired/released twice when we take the _lock_unlock_module() path. IMHO it isn't an issue, I prefer finer grain lock.
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Even with your improvements to the lock handling, this still looks a bit race-prone to me, since we have the classic "query before use" pattern of:
That is, just because the module was there when we checked
if name not in sys.modules
doesn't mean it's still going to be there when we runmodule = sys.modules[name]
.Previously, holding
_imp.acquire_lock()
for the whole function would at least protect this from other_find_and_load()
calls, but as far as I can see it's never been protected from other threads doingdel sys.modules[name]
without holding the relevant module lock.There was a problem hiding this comment.
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Oh, you are right: I proposed PR #2665.