app/django/contrib/sessions/backends/cache.py

   1 from django.contrib.sessions.backends.base import SessionBase, CreateError
   2 from django.core.cache import cache
   3
   4 class SessionStore(SessionBase):
   5     """
   6     A cache-based session store.
   7     """
   8     def __init__(self, session_key=None):
   9         self._cache = cache
  10         super(SessionStore, self).__init__(session_key)
  11
  12     def load(self):
  13         session_data = self._cache.get(self.session_key)
  14         if session_data is not None:
  15             return session_data
  16         self.create()
  17         return {}
  18
  19     def create(self):
  20         # Because a cache can fail silently (e.g. memcache), we don't know if
  21         # we are failing to create a new session because of a key collision or
  22         # because the cache is missing. So we try for a (large) number of times
  23         # and then raise an exception. That's the risk you shoulder if using
  24         # cache backing.
  25         for i in xrange(10000):
  26             self.session_key = self._get_new_session_key()
  27             try:
  28                 self.save(must_create=True)
  29             except CreateError:
  30                 continue
  31             self.modified = True
  32             return
  33         raise RuntimeError("Unable to create a new session key.")
  34
  35     def save(self, must_create=False):
  36         if must_create:
  37             func = self._cache.add
  38         else:
  39             func = self._cache.set
  40         result = func(self.session_key, self._get_session(no_load=must_create),
  41                 self.get_expiry_age())
  42         if must_create and not result:
  43             raise CreateError
  44
  45     def exists(self, session_key):
  46         if self._cache.get(session_key):
  47             return True
  48         return False
  49
  50     def delete(self, session_key=None):
  51         if session_key is None:
  52             if self._session_key is None:
  53                 return
  54             session_key = self._session_key
  55         self._cache.delete(session_key)
  56