Opened 2 years ago
Last modified 2 years ago
#34209 closed Bug
FileBasedCache has_key is susceptible to race conditions — at Initial Version
Reported by: | Marti Raudsepp | Owned by: | nobody |
---|---|---|---|
Component: | Core (Cache system) | Version: | 4.1 |
Severity: | Normal | Keywords: | race, race-condition, FileBasedCache |
Cc: | Triage Stage: | Ready for checkin | |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
I received the exception from Django's cache framework:
FileNotFoundError: [Errno 2] No such file or directory: '/app/var/cache/d729e4cf4ba88cba5a0f48e0396ec48a.djcache' [...] File "django/core/cache/backends/base.py", line 229, in get_or_set self.add(key, default, timeout=timeout, version=version) File "django/core/cache/backends/filebased.py", line 26, in add if self.has_key(key, version): File "django/core/cache/backends/filebased.py", line 94, in has_key with open(fname, "rb") as f:
The code is:
def has_key(self, key, version=None): fname = self._key_to_file(key, version) if os.path.exists(fname): with open(fname, "rb") as f: return not self._is_expired(f) return False
Between the exists()
check and open()
, it's possible for the file to be deleted. In fact, the _is_expired()
method itself deletes the file if it finds it to be expired. So if many threads race to read an expired cache at once, it's not that unlikely to hit this window.
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