--- a/app/django/contrib/sessions/backends/cache.py	Tue Oct 14 12:36:55 2008 +0000
+++ b/app/django/contrib/sessions/backends/cache.py	Tue Oct 14 16:00:59 2008 +0000
@@ -1,26 +1,56 @@
-from django.conf import settings
-from django.contrib.sessions.backends.base import SessionBase
+from django.contrib.sessions.backends.base import SessionBase, CreateError
 from django.core.cache import cache
 
 class SessionStore(SessionBase):
     """
-    A cache-based session store. 
+    A cache-based session store.
     """
     def __init__(self, session_key=None):
         self._cache = cache
         super(SessionStore, self).__init__(session_key)
-        
+
     def load(self):
         session_data = self._cache.get(self.session_key)
-        return session_data or {}
+        if session_data is not None:
+            return session_data
+        self.create()
+        return {}
 
-    def save(self):
-        self._cache.set(self.session_key, self._session, settings.SESSION_COOKIE_AGE)
+    def create(self):
+        # Because a cache can fail silently (e.g. memcache), we don't know if
+        # we are failing to create a new session because of a key collision or
+        # because the cache is missing. So we try for a (large) number of times
+        # and then raise an exception. That's the risk you shoulder if using
+        # cache backing.
+        for i in xrange(10000):
+            self.session_key = self._get_new_session_key()
+            try:
+                self.save(must_create=True)
+            except CreateError:
+                continue
+            self.modified = True
+            return
+        raise RuntimeError("Unable to create a new session key.")
+
+    def save(self, must_create=False):
+        if must_create:
+            func = self._cache.add
+        else:
+            func = self._cache.set
+        result = func(self.session_key, self._get_session(no_load=must_create),
+                self.get_expiry_age())
+        if must_create and not result:
+            raise CreateError
 
     def exists(self, session_key):
         if self._cache.get(session_key):
             return True
         return False
-        
-    def delete(self, session_key):
-        self._cache.delete(session_key)
\ No newline at end of file
+
+    def delete(self, session_key=None):
+        if session_key is None:
+            if self._session_key is None:
+                return
+            session_key = self._session_key
+        self._cache.delete(session_key)
+