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Refs #28593 -- Made URLResolver._populate() more resilient to signal interrupts. 

_populate() sets the populating attribute to prevent infinite recursion in
case a urlconf includes itself. The flag is a threadlocal to avoid a race
condition [1] where one thread sets the flag and another checks it, then
proceeds to access data that's supposed to be populated (e.g. _reverse_dict)
but isn't yet.

The potential still exists for a thread to set the threadlocal, then be
interrupted by a signal such as SIGALRM and raise before resetting the
threadlocal flag. In this scenario, subsequent calls to _populate() in the
same thread will short-circuit erroneously.

The bulk of the method was already wrapped in a try/finally in df41b5a, but
since a signal interrupt can occur at any line executed by the interpreter,
this moves up the try to ensure threadlocal gets reset.

[1]: https://groups.google.com/d/msg/django-developers/D_bIeinKHjE/4NmVQUJqAgAJ
This commit is contained in:
Daniel Tao 2017-09-22 07:43:00 -05:00 committed by Tim Graham
parent 771e06af2a
commit 6f7279c4b1
1 changed files with 5 additions and 5 deletions
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2
django/urls/resolvers.py
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@ -398,12 +398,12 @@ class URLResolver:
# thread-local variable. # thread-local variable.
if getattr(self._local, 'populating', False): if getattr(self._local, 'populating', False):
return return
try:
self._local.populating = True self._local.populating = True
lookups = MultiValueDict() lookups = MultiValueDict()
namespaces = {} namespaces = {}
apps = {} apps = {}
language_code = get_language() language_code = get_language()
try:
for url_pattern in reversed(self.url_patterns): for url_pattern in reversed(self.url_patterns):
p_pattern = url_pattern.pattern.regex.pattern p_pattern = url_pattern.pattern.regex.pattern
if p_pattern.startswith('^'): if p_pattern.startswith('^'):