text: # Copyright 2013 Metacloud
  #
  # Licensed under the Apache License, Version 2.0 (the "License"); you may
  # not use this file except in compliance with the License. You may obtain
  # a copy of the License at
  #
  #      http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  # License for the specific language governing permissions and limitations
  # under the License.
  
  from dogpile.cache import api
  from oslo_log import versionutils
  
  
  NO_VALUE = api.NO_VALUE
  
  
  @versionutils.deprecated(
      versionutils.deprecated.MITAKA,
      what='keystone.common.cache.noop backend',
      in_favor_of="dogpile.cache's Null backend",
      remove_in=+1)
  class NoopCacheBackend(api.CacheBackend):
      """A no op backend as a default caching backend.
  
      The no op backend is provided as the default caching backend for keystone
      to ensure that ``dogpile.cache.memory`` is not used in any real-world
      circumstances unintentionally.  ``dogpile.cache.memory`` does not have a
      mechanism to cleanup it's internal dict and therefore could cause run-away
      memory utilization.
      """
      def __init__(self, *args):
          return
  
      def get(self, key):
          return NO_VALUE
  
      def get_multi(self, keys):
          return [NO_VALUE for x in keys]
  
      def set(self, key, value):
          return
  
      def set_multi(self, mapping):
          return
  
      def delete(self, key):
          return
  
      def delete_multi(self, keys):
          return
  