Opened 22 months ago
Closed 22 months ago
#34276 closed Bug (invalid)
LocMemCache not working for multiple threads
Reported by: | D Bersan | Owned by: | nobody |
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Component: | Core (Cache system) | Version: | 4.1 |
Severity: | Normal | Keywords: | LocMemCache |
Cc: | Triage Stage: | Unreviewed | |
Has patch: | no | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description (last modified by )
I have a thread that is initialized on apps.py in a given app in django.
This thread updates the value of a counter
that is saved in cache, using django.core.cache
.
Also I have a view that returns the value of the same cache, in an endpoint:
# jobs.py import threading import time from django.core.cache import cache class MyThread: def __init__(self) -> None: self.t = threading.Thread(target=MyThread.myLoop, args=(self,)) self.t.daemon = True self.count = 1 def myLoop(self): while self.running: time.sleep(3) self.count += 1 cache.set('count', self.count) def start(self): self.running = True self.t.start() def stop(self): self.running = False # -------------- # apps.py from django.apps import AppConfig import os class MyAppConfig(AppConfig): default_auto_field = "django.db.models.BigAutoField" name = "MyApp" def ready(self) -> None: from .jobs import MyThread t= MyThread() if os.environ.get('RUN_MAIN', None) != 'true': t.start() # return super().ready() # -------------- # views.py from django.http import JsonResponse from django.core.cache import cache # ... other imports def getCurrentCount(request): global cache if request.method == 'GET': return JsonResponse({ 'count': cache.get('count') })
I am using (LocMemCache)https://docs.djangoproject.com/en/4.1/topics/cache/#local-memory-caching in settings.py:
CACHES = { 'default': { 'BACKEND': 'django.core.cache.backends.locmem.LocMemCache', 'LOCATION': 'unique-snowflake', } }
But when I try to log the result of cache.get('count')
, it returns None
.
The documentation clearly states:
"This cache is per-process (see below) and thread-safe."
"Note that each process will have its own private cache instance, which means no cross-process caching is possible. "
I have the impression that they meant the cache is per-thread , not per-process . Both my threads are on the same process, so they should share the same caching, according to the documentation. It also emphasizes, no cross-process caching is possible. It doesn't say no cross-threading caching is possible. But reading other resources I found online, it seems this is not shared even among threads, so the documentation is wrong, or there is a bug in this version of Django.
Change History (3)
comment:1 by , 22 months ago
Description: | modified (diff) |
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comment:2 by , 22 months ago
Description: | modified (diff) |
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comment:3 by , 22 months ago
Component: | Uncategorized → Core (Cache system) |
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Resolution: | → invalid |
Status: | new → closed |
The
LocMemCache
cache is safe -- each process and thread gets its own cache, so there's no chances of conflicts (see comment).There is nothing in the docs about sharing the same cache instance between processes or threads.
I would argue that documentation doesn't need to mention everything that it's not possible. It's also documented: