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# Copyright 2013 Metacloud, Inc.
#
# 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.
"""
Keystone Memcached dogpile.cache backend implementation.
"""
import random as _random
import time
from dogpile.cache import api
from dogpile.cache.backends import memcached
from oslo_config import cfg
from oslo_log import log
from six.moves import range
from keystone.common.cache.backends import memcache_pool
from keystone import exception
from keystone.i18n import _
CONF = cfg.CONF
LOG = log.getLogger(__name__)
NO_VALUE = api.NO_VALUE
random = _random.SystemRandom()
VALID_DOGPILE_BACKENDS = dict(
pylibmc=memcached.PylibmcBackend,
bmemcached=memcached.BMemcachedBackend,
memcached=memcached.MemcachedBackend,
pooled_memcached=memcache_pool.PooledMemcachedBackend)
class MemcachedLock(object):
"""Simple distributed lock using memcached.
This is an adaptation of the lock featured at
http://amix.dk/blog/post/19386
"""
def __init__(self, client_fn, key, lock_timeout, max_lock_attempts):
self.client_fn = client_fn
self.key = "_lock" + key
self.lock_timeout = lock_timeout
self.max_lock_attempts = max_lock_attempts
def acquire(self, wait=True):
client = self.client_fn()
for i in range(self.max_lock_attempts):
if client.add(self.key, 1, self.lock_timeout):
return True
elif not wait:
return False
else:
sleep_time = random.random()
time.sleep(sleep_time)
raise exception.UnexpectedError(
_('Maximum lock attempts on %s occurred.') % self.key)
def release(self):
client = self.client_fn()
client.delete(self.key)
class MemcachedBackend(object):
"""Pivot point to leverage the various dogpile.cache memcached backends.
To specify a specific dogpile.cache memcached backend, pass the argument
`memcached_backend` set to one of the provided memcached backends (at this
time `memcached`, `bmemcached`, `pylibmc` and `pooled_memcached` are
valid).
"""
def __init__(self, arguments):
self._key_mangler = None
self.raw_no_expiry_keys = set(arguments.pop('no_expiry_keys', set()))
self.no_expiry_hashed_keys = set()
self.lock_timeout = arguments.pop('lock_timeout', None)
self.max_lock_attempts = arguments.pop('max_lock_attempts', 15)
# NOTE(morganfainberg): Remove distributed locking from the arguments
# passed to the "real" backend if it exists.
arguments.pop('distributed_lock', None)
backend = arguments.pop('memcached_backend', None)
if 'url' not in arguments:
# FIXME(morganfainberg): Log deprecation warning for old-style
# configuration once full dict_config style configuration for
# KVS backends is supported. For now use the current memcache
# section of the configuration.
arguments['url'] = CONF.memcache.servers
if backend is None:
# NOTE(morganfainberg): Use the basic memcached backend if nothing
# else is supplied.
self.driver = VALID_DOGPILE_BACKENDS['memcached'](arguments)
else:
if backend not in VALID_DOGPILE_BACKENDS:
raise ValueError(
_('Backend `%(backend)s` is not a valid memcached '
'backend. Valid backends: %(backend_list)s') %
{'backend': backend,
'backend_list': ','.join(VALID_DOGPILE_BACKENDS.keys())})
else:
self.driver = VALID_DOGPILE_BACKENDS[backend](arguments)
def __getattr__(self, name):
"""Forward calls to the underlying driver."""
f = getattr(self.driver, name)
setattr(self, name, f)
return f
def _get_set_arguments_driver_attr(self, exclude_expiry=False):
# NOTE(morganfainberg): Shallow copy the .set_arguments dict to
# ensure no changes cause the values to change in the instance
# variable.
set_arguments = getattr(self.driver, 'set_arguments', {}).copy()
if exclude_expiry:
# NOTE(morganfainberg): Explicitly strip out the 'time' key/value
# from the set_arguments in the case that this key isn't meant
# to expire
set_arguments.pop('time', None)
return set_arguments
def set(self, key, value):
mapping = {key: value}
self.set_multi(mapping)
def set_multi(self, mapping):
mapping_keys = set(mapping.keys())
no_expiry_keys = mapping_keys.intersection(self.no_expiry_hashed_keys)
has_expiry_keys = mapping_keys.difference(self.no_expiry_hashed_keys)
if no_expiry_keys:
# NOTE(morganfainberg): For keys that have expiry excluded,
# bypass the backend and directly call the client. Bypass directly
# to the client is required as the 'set_arguments' are applied to
# all ``set`` and ``set_multi`` calls by the driver, by calling
# the client directly it is possible to exclude the ``time``
# argument to the memcached server.
new_mapping = {k: mapping[k] for k in no_expiry_keys}
set_arguments = self._get_set_arguments_driver_attr(
exclude_expiry=True)
self.driver.client.set_multi(new_mapping, **set_arguments)
if has_expiry_keys:
new_mapping = {k: mapping[k] for k in has_expiry_keys}
self.driver.set_multi(new_mapping)
@classmethod
def from_config_dict(cls, config_dict, prefix):
prefix_len = len(prefix)
return cls(
{key[prefix_len:]: config_dict[key] for key in config_dict
if key.startswith(prefix)})
@property
def key_mangler(self):
if self._key_mangler is None:
self._key_mangler = self.driver.key_mangler
return self._key_mangler
@key_mangler.setter
def key_mangler(self, key_mangler):
if callable(key_mangler):
self._key_mangler = key_mangler
self._rehash_keys()
elif key_mangler is None:
# NOTE(morganfainberg): Set the hashed key map to the unhashed
# list since we no longer have a key_mangler.
self._key_mangler = None
self.no_expiry_hashed_keys = self.raw_no_expiry_keys
else:
raise TypeError(_('`key_mangler` functions must be callable.'))
def _rehash_keys(self):
no_expire = set()
for key in self.raw_no_expiry_keys:
no_expire.add(self._key_mangler(key))
self.no_expiry_hashed_keys = no_expire
def get_mutex(self, key):
return MemcachedLock(lambda: self.driver.client, key,
self.lock_timeout, self.max_lock_attempts)
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