#33252: CacheMiddleware is not thread safe
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Reporter: Iuri de Silvio | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 3.2
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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CacheMiddleware persist `self.cache = caches[cache_alias]` on startup and
it is not thread safe.
https://github.com/django/django/blob/main/django/middleware/cache.py#L186
I found that after some production errors with pylibmc and uwsgi threaded.
Created a small project to reproduce it. Nothing fancy, just pylibmc cache
and a `@cache_page` cached view. It fails even with development server,
with concurrent requests.
{{{
Traceback (most recent call last):
File "versions/pylibmcbug/lib/python3.9/site-
packages/django/core/handlers/exception.py", line 47, in inner
response = get_response(request)
File "versions/pylibmcbug/lib/python3.9/site-
packages/django/core/handlers/base.py", line 181, in _get_response
response = wrapped_callback(request, *callback_args,
**callback_kwargs)
File "versions/pylibmcbug/lib/python3.9/site-
packages/django/utils/decorators.py", line 122, in _wrapped_view
result = middleware.process_request(request)
File "versions/pylibmcbug/lib/python3.9/site-
packages/django/middleware/cache.py", line 145, in process_request
cache_key = get_cache_key(request, self.key_prefix, 'GET',
cache=self.cache)
File "versions/pylibmcbug/lib/python3.9/site-
packages/django/utils/cache.py", line 362, in get_cache_key
headerlist = cache.get(cache_key)
File "versions/pylibmcbug/lib/python3.9/site-
packages/django/core/cache/backends/memcached.py", line 77, in get
return self._cache.get(key, default)
pylibmc.ConnectionError: error 3 from
memcached_get(:1:views.decorators.cache.cache_): (0x7f290400bd60) FAILURE,
poll() returned a value that was not dealt with, host: localhost:11211 ->
libmemcached/io.cc:254
}}}
Looking for git history, it is this way since 2010.
https://github.com/django/django/commit/673e6fc7fb243ed44841b9969d26a161c25733b3
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Ticket URL: <https://code.djangoproject.com/ticket/33252>
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