fix for a deadlock in the logging module

[sprause]

BPO	1158052
Nosy	@vsajip
Files	logging_deadlock.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/vsajip'
closed_at = <Date 2005-03-13.09:59:26.000>
created_at = <Date 2005-03-07.03:28:50.000>
labels = ['library']
title = 'fix for a deadlock in the logging module'
updated_at = <Date 2005-03-13.09:59:26.000>
user = 'https://bugs.python.org/sprause'

bugs.python.org fields:

activity = <Date 2005-03-13.09:59:26.000>
actor = 'vinay.sajip'
assignee = 'vinay.sajip'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2005-03-07.03:28:50.000>
creator = 'sprause'
dependencies = []
files = ['6525']
hgrepos = []
issue_num = 1158052
keywords = ['patch']
message_count = 3.0
messages = ['47883', '47884', '47885']
nosy_count = 2.0
nosy_names = ['vinay.sajip', 'sprause']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1158052'
versions = []

[sprause]

there is a deadlock in the logging package, that can be
triggered with a custom class importer:

(1) create a custom class importer and put it in
sys.meta_path (this importer must log a message via the
logging package)
(2) raise an exception somewhere and log it
(3) when the formatter tries to format the exception,
it imports the traceback module (in the formatException
method)
(4) this import will be redirected to the above
installed class importer
(5) the class importer tries to log a message
(6) trying to acquire the lock for the new log message
in Handler.acquire results in a deadlock

the fix is to move the traceback import from the method
to the module, so it gets imported when no lock is
held. the attached patch does this

[sprause]

Logged In: YES
user_id=925608

SMTPHandler and HTTPHandler have the same problem, as they
import modules in the emit() method...

[vsajip]

Logged In: YES
user_id=308438

Fix checked into CVS, thanks.