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OpenStack Study: memcached.py**** CubicPower OpenStack Study ****
# 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 import time from dogpile.cache import api from dogpile.cache.backends import memcached from keystone.common import manager from keystone import config from keystone import exception from keystone.openstack.common.gettextutils import _ from keystone.openstack.common import log CONF = config.CONF LOG = log.getLogger(__name__) NO_VALUE = api.NO_VALUE VALID_DOGPILE_BACKENDS = dict(pylibmc=memcached.PylibmcBackend, bmemcached=memcached.BMemcachedBackend, memcached=memcached.MemcachedBackend)
**** CubicPower OpenStack Study **** class MemcachedLock(object): """Simple distributed lock using memcached. This is an adaptation of the lock featured at http://amix.dk/blog/post/19386 """
**** CubicPower OpenStack Study **** 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
**** CubicPower OpenStack Study **** def acquire(self, wait=True): client = self.client_fn() i = 0 while True: if client.add(self.key, 1, self.lock_timeout): return True elif not wait: return False else: sleep_time = (((i + 1) * random.random()) + 2 ** i) / 2.5 time.sleep(sleep_time) if i <= self.max_lock_attempts: i += 1 else: raise exception.UnexpectedError( _('Maximum lock attempts on %s occurred.') % self.key)
**** CubicPower OpenStack Study **** def release(self): client = self.client_fn() client.delete(self.key)
**** CubicPower OpenStack Study **** class MemcachedBackend(manager.Manager): """Pivot point to leverage the various dogpile.cache memcached backends. To specify a specific dogpile.cache memcached driver, pass the argument `memcached_driver` set to one of the provided memcached drivers (at this time `memcached`, `bmemcached`, `pylibmc` are valid). """
**** CubicPower OpenStack Study **** 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 `%(driver)s` is not a valid memcached ' 'backend. Valid drivers: %(driver_list)s') % {'driver': backend, 'driver_list': ','.join(VALID_DOGPILE_BACKENDS.keys())}) else: self.driver = VALID_DOGPILE_BACKENDS[backend](arguments)
**** CubicPower OpenStack Study **** 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
**** CubicPower OpenStack Study **** def set(self, key, value): mapping = {key: value} self.set_multi(mapping)
**** CubicPower OpenStack Study **** 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 = dict((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 = dict((k, mapping[k]) for k in has_expiry_keys) self.driver.set_multi(new_mapping) @classmethod
**** CubicPower OpenStack Study **** def from_config_dict(cls, config_dict, prefix): prefix_len = len(prefix) return cls( dict((key[prefix_len:], config_dict[key]) for key in config_dict if key.startswith(prefix))) @property
**** CubicPower OpenStack Study **** def key_mangler(self): if self._key_mangler is None: self._key_mangler = self.driver.key_mangler return self._key_mangler @key_mangler.setter
**** CubicPower OpenStack Study **** 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.'))
**** CubicPower OpenStack Study **** 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
**** CubicPower OpenStack Study **** def get_mutex(self, key): return MemcachedLock(lambda: self.driver.client, key, self.lock_timeout, self.max_lock_attempts)
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