Description

assignee = 'https://github.com/birkenfeld'
closed_at = <Date 2010-04-02.17:54:34.865>
created_at = <Date 2009-08-05.04:52:59.012>
labels = ['type-bug', 'library', 'docs']
title = 'warnings.catch_warnings is not thread-safe'
updated_at = <Date 2010-04-02.17:54:34.862>
user = 'https://bugs.python.org/ggenellina'

activity = <Date 2010-04-02.17:54:34.862>
actor = 'akuchling'
assignee = 'georg.brandl'
closed = True
closed_date = <Date 2010-04-02.17:54:34.865>
closer = 'akuchling'
components = ['Documentation', 'Library (Lib)']
creation = <Date 2009-08-05.04:52:59.012>
creator = 'ggenellina'
dependencies = []
files = ['14654', '15341']
hgrepos = []
issue_num = 6647
keywords = ['patch']
message_count = 4.0
messages = ['91301', '91318', '95285', '102185']
nosy_count = 4.0
nosy_names = ['akuchling', 'georg.brandl', 'ggenellina', 'pitrou']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue6647'
versions = ['Python 2.6', 'Python 3.1', 'Python 2.7', 'Python 3.2']

Activity

1. ggenellina commented on Aug 5, 2009

   

   ggenellinamannequin

   on Aug 5, 2009

   MannequinAuthor

   More actions

   warnings.catch_warnings is a context manager supposed to save and
   restore warnings filters, and optionally record all warnings issued.

   But it does so in a completely thread-unsafe way, by replacing the
   module's "showwarning" and "filters" attributes on enter, and restoring
   them on exit. If the __enter__ / __exit__ calls of two threads overlap,
   after leaving the last block the warnings state is not the same as the
   original state, as it should be.

   I don't know how to fix this, other than using locks (that could block
   indefinitely) or severely restricting how catch_warnings may be used.
   At least, this issue should be documented.
2. ggenellina

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Aug 5, 2009
3. pitrou commented on Aug 5, 2009

   

   pitrou

   on Aug 5, 2009

   Member

   More actions

   Any function whose purpose is to mutate global (non thread-local) state
   is inherently "thread-unsafe". The only reasonable possibility is to
   document it as such.
4. pitrou

   added

   docsDocumentation in the Doc dirDocumentation in the Doc dir

   on Aug 5, 2009
5. pitrou

   assigned

   birkenfeld

   on Aug 5, 2009
6. ggenellina commented on Nov 15, 2009

   

   ggenellinamannequin

   on Nov 15, 2009

   MannequinAuthor

   More actions

   Document that warnings.catch_warnings is not thread safe.
7. akuchling commented on Apr 2, 2010

   

   akuchling

   on Apr 2, 2010

   Contributor

   More actions

   Added a warning to 2.x trunk in r79607, and Gabriel's doc change in r79608. This thread-unsafety seems specialized and rarely of great importance, so I used the note:: directive, not warning::.
8. akuchling

   closed this as completedon Apr 2, 2010
9. ezio-melotti

   transferred this issue fromon Apr 10, 2022

Issue actions