[New-bugs-announce] [issue21149] logging._removeHandlerRef is not threadsafe during interpreter shutdown

[Devin Jeanpierre]

New submission from Devin Jeanpierre:

If another thread is active during interpreter shutdown, it can hold the last reference to a handler; when it drops that reference, the weakref callback -- _removeHandlerRef -- will be executed in this other thread. So while this callback is running, the main thread is replacing module globals with None. This creates a data race for the globals in logging -- for example, _releaseLock can be replaced with None after the "_releaseLock is not None" check, but before it is used.

In principle I suspect this could cause a deadlock, in practice all I've seen are exception messages mentioning how None is not callable.

I have attached a patch that I think resolves this issue. The patch is written against 2.7, although I expect this issue affects all versions of Python prior to 3.4

BTW, the copyright for this patch belongs to my employer, Google; please let me know if there are any contributor agreements or such that my employer needs to look at.

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components: Library (Lib)
files: patch.diff
keywords: patch
messages: 215466
nosy: Devin Jeanpierre, gregory.p.smith
priority: normal
severity: normal
status: open
title: logging._removeHandlerRef is not threadsafe during interpreter shutdown
versions: Python 2.7
Added file: http://bugs.python.org/file34718/patch.diff

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<http://bugs.python.org/issue21149>
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