summaryrefslogtreecommitdiffstats
path: root/keystone-moon/keystone/common/kvs/backends/memcached.py
blob: f54c1a01720e9172e5a739c4416c45129d33a606 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
# 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)