Connect post_save signals where they will always be triggered

We need to do this in the models.py files, otherwise the post_save signal
might not be connected right away on launch of the application. Move them
over there, add a dispatch_uid so it only gets hooked up once, and do some
other function moving around so we don't have circular imports.

Signed-off-by: Dan McGee <dan@archlinux.org>

2 files changed, 29 insertions, 1 deletions

diff --git a/main/models.py b/main/models.py
index dc700fb..888f0b8 100644
--- a/main/models.py
+++ b/main/models.py
@@ -325,4 +325,10 @@ class TodolistPkg(models.Model):
         db_table = 'todolist_pkgs'
         unique_together = (('list','pkg'),)
 
+# connect signals needed to keep cache in line with reality
+from main.utils import refresh_package_latest
+from django.db.models.signals import post_save
+post_save.connect(refresh_package_latest, sender=Package,
+        dispatch_uid="main.models")
+
 # vim: set ts=4 sw=4 et:
diff --git a/main/utils.py b/main/utils.py
index ae446ab..d7681cb 100644
--- a/main/utils.py
+++ b/main/utils.py
@@ -5,6 +5,12 @@ except ImportError:
 from django.core.cache import cache
 from django.utils.hashcompat import md5_constructor
 
+CACHE_TIMEOUT = 1800
+INVALIDATE_TIMEOUT = 15
+
+CACHE_PACKAGE_KEY = 'cache_package_latest'
+CACHE_NEWS_KEY = 'cache_news_latest'
+
 def cache_function_key(func, args, kwargs):
     raw = [func.__name__, func.__module__, args, kwargs]
     pickled = pickle.dumps(raw, protocol=pickle.HIGHEST_PROTOCOL)
@@ -40,7 +46,23 @@ def clear_cache_function(func, args, kwargs):
     key = cache_function_key(func, args, kwargs)
     cache.delete(key)
 
-#utility to make a pair of django choices
+# utility to make a pair of django choices
 make_choice = lambda l: [(str(m), str(m)) for m in l]
 
+# These are in here because we would be jumping around in some import circles
+# and hoops otherwise. The only thing currently using these keys is the feed
+# caching stuff.
+
+def refresh_package_latest(**kwargs):
+    # We could delete the value, but that could open a race condition
+    # where the new data wouldn't have been committed yet by the calling
+    # thread. Instead, explicitly set it to None for a short amount of time.
+    # Hopefully by the time it expires we will have committed, and the cache
+    # will be valid again. See "Scaling Django" by Mike Malone, slide 30.
+    cache.set(CACHE_PACKAGE_KEY, None, INVALIDATE_TIMEOUT)
+
+def refresh_news_latest(**kwargs):
+    # same thoughts apply as in refresh_package_latest
+    cache.set(CACHE_NEWS_KEY, None, INVALIDATE_TIMEOUT)
+
 # vim: set ts=4 sw=4 et: