Use Django's cache framework for task keys.

Remove depreciated only_one decorator.

Prevent including task_self repr in key name.

Because some tasks are nested in a class, they use a task_self argument instead of the normal self which the celery_once package doesn't recognize to strip out.

allianceauth/project_template/project_name/celery.py

@@ -12,11 +12,8 @@ app = Celery('{{ project_name }}')
 # the configuration object to child processes.
 app.config_from_object('django.conf:settings')
 app.conf.ONCE = {
-  'backend': 'celery_once.backends.Redis',
-  'settings': {
-    'url': 'redis://localhost:6379/0',
-    'default_timeout': 60 * 60
-  }
+    'backend': 'allianceauth.services.tasks.DjangoBackend',
+    'settings': {}
 }
 
 # Load task modules from all registered Django app configs.

allianceauth/services/tasks.py

@@ -1,12 +1,13 @@
 import logging
 
-import redis
-from celery import shared_task
+from celery import shared_task, Task
 from django.contrib.auth.models import User
 from .hooks import ServicesHook
-from celery_once import QueueOnce as BaseTask
+from celery_once import QueueOnce as BaseTask, AlreadyQueued
+from celery_once.helpers import now_unix, queue_once_key
+from django.core.cache import cache
+from inspect import getcallargs
 
-REDIS_CLIENT = redis.Redis()
 
 logger = logging.getLogger(__name__)
 
@@ -15,32 +16,41 @@ class QueueOnce(BaseTask):
     once = BaseTask.once
     once['graceful'] = True
 
+    def get_key(self, args=None, kwargs=None):
+        """
+        Generate the key from the name of the task (e.g. 'tasks.example') and
+        args/kwargs.
+        """
+        restrict_to = self.once.get('keys', None)
+        args = args or {}
+        kwargs = kwargs or {}
+        call_args = getcallargs(self.run, *args, **kwargs)
 
-# http://loose-bits.com/2010/10/distributed-task-locking-in-celery.html
-def only_one(function=None, key="", timeout=None):
-    """Enforce only one celery task at a time."""
+        if isinstance(call_args.get('self'), Task):
+            del call_args['self']
+        if isinstance(call_args.get('task_self'), Task):
+            del call_args['task_self']
+        return queue_once_key(self.name, call_args, restrict_to)
 
-    def _dec(run_func):
-        """Decorator."""
 
-        def _caller(*args, **kwargs):
-            """Caller."""
-            ret_value = None
-            have_lock = False
-            lock = REDIS_CLIENT.lock(key, timeout=timeout)
-            try:
-                have_lock = lock.acquire(blocking=False)
-                if have_lock:
-                    ret_value = run_func(*args, **kwargs)
-            finally:
-                if have_lock:
-                    lock.release()
+class DjangoBackend:
+    def __init__(self, settings):
+        pass
 
-            return ret_value
+    @staticmethod
+    def raise_or_lock(key, timeout):
+        now = now_unix()
+        result = cache.get(key)
+        if result:
+            remaining = int(result) - now
+            if remaining > 0:
+                raise AlreadyQueued(remaining)
+        else:
+            cache.set(key, now + timeout, timeout)
 
-        return _caller
-
-    return _dec(function) if function is not None else _dec
+    @staticmethod
+    def clear_lock(key):
+        return cache.delete(key)
 
 
 @shared_task(bind=True)

tests/celery.py

@@ -1,4 +1,4 @@
-import os, sys
+import os
 from celery import Celery
 
 # set the default Django settings module for the 'celery' program.
@@ -7,17 +7,15 @@ os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'settings')
 from django.conf import settings  # noqa
 
 app = Celery('devauth')
-app.conf.ONCE = {
-  'backend': 'celery_once.backends.Redis',
-  'settings': {
-    'url': 'redis://localhost:6379/0',
-    'default_timeout': 60 * 60
-  }
-}
 
 # Using a string here means the worker don't have to serialize
 # the configuration object to child processes.
 app.config_from_object('django.conf:settings')
+app.conf.ONCE = {
+    'backend': 'allianceauth.services.tasks.DjangoBackend',
+    'settings': {}
+}
 
 # Load task modules from all registered Django app configs.
 app.autodiscover_tasks(lambda: settings.INSTALLED_APPS)
+