# -*- coding: utf-8 -*-
#
# Copyright © 2014 eNovance
#
# 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.
import contextlib
import errno
import functools
import logging
import socket
from oslo_utils import encodeutils
from pymemcache import client as pymemcache_client
import tooz
from tooz import _retry
from tooz import coordination
from tooz import locking
from tooz import utils
LOG = logging.getLogger(__name__)
@contextlib.contextmanager
def _failure_translator():
"""Translates common pymemcache exceptions into tooz exceptions.
https://github.com/pinterest/pymemcache/blob/d995/pymemcache/client.py#L202
"""
try:
yield
except pymemcache_client.MemcacheUnexpectedCloseError as e:
utils.raise_with_cause(coordination.ToozConnectionError,
encodeutils.exception_to_unicode(e),
cause=e)
except (socket.timeout, socket.error,
socket.gaierror, socket.herror) as e:
# TODO(harlowja): get upstream pymemcache to produce a better
# exception for these, using socket (vs. a memcache specific
# error) seems sorta not right and/or the best approach...
msg = encodeutils.exception_to_unicode(e)
if e.errno is not None:
msg += " (with errno %s [%s])" % (errno.errorcode[e.errno],
e.errno)
utils.raise_with_cause(coordination.ToozConnectionError,
msg, cause=e)
except pymemcache_client.MemcacheError as e:
utils.raise_with_cause(tooz.ToozError,
encodeutils.exception_to_unicode(e),
cause=e)
def _translate_failures(func):
@functools.wraps(func)
def wrapper(*args, **kwargs):
with _failure_translator():
return func(*args, **kwargs)
return wrapper
class MemcachedLock(locking.Lock):
_LOCK_PREFIX = b'__TOOZ_LOCK_'
def __init__(self, coord, name, timeout):
super(MemcachedLock, self).__init__(self._LOCK_PREFIX + name)
self.coord = coord
self.timeout = timeout
def is_still_owner(self):
if not self.acquired:
return False
else:
owner = self.get_owner()
if owner is None:
return False
return owner == self.coord._member_id
def acquire(self, blocking=True, shared=False):
if shared:
raise tooz.NotImplemented
@_retry.retry(stop_max_delay=blocking)
@_translate_failures
def _acquire():
if self.coord.client.add(
self.name,
self.coord._member_id,
expire=self.timeout,
noreply=False):
self.coord._acquired_locks.append(self)
return True
if blocking is False:
return False
raise _retry.TryAgain
return _acquire()
@_translate_failures
def break_(self):
return bool(self.coord.client.delete(self.name, noreply=False))
@_translate_failures
def release(self):
if not self.acquired:
return False
# NOTE(harlowja): this has the potential to delete others locks
# especially if this key expired before the delete/release call is
# triggered.
#
# For example:
#
# 1. App #1 with coordinator 'A' acquires lock "b"
# 2. App #1 heartbeats every 10 seconds, expiry for lock let's
# say is 11 seconds.
# 3. App #2 with coordinator also named 'A' blocks trying to get
# lock "b" (let's say it retries attempts every 0.5 seconds)
# 4. App #1 is running behind a little bit, tries to heartbeat but
# key has expired (log message is written); at this point app #1
# doesn't own the lock anymore but it doesn't know that.
# 5. App #2 now retries and adds the key, and now it believes it
# has the lock.
# 6. App #1 (still believing it has the lock) calls release, and
# deletes app #2 lock, app #2 now doesn't own the lock anymore
# but it doesn't know that and now app #(X + 1) can get it.
# 7. App #2 calls release (repeat #6 as many times as desired)
#
# Sadly I don't think memcache has the primitives to actually make
# this work, redis does because it has lua which can check a session
# id and then do the delete and bail out if the session id is not
# as expected but memcache doesn't seem to have any equivalent
# capability.
if self not in self.coord._acquired_locks:
return False
# Do a ghetto test to see what the value is... (see above note),
# and how this really can't be done safely with memcache due to
# it being done in the client side (non-atomic).
value = self.coord.client.get(self.name)
if value != self.coord._member_id:
return False
else:
was_deleted = self.coord.client.delete(self.name, noreply=False)
if was_deleted:
self.coord._acquired_locks.remove(self)
return was_deleted
@_translate_failures
def heartbeat(self):
"""Keep the lock alive."""
if self.acquired:
poked = self.coord.client.touch(self.name,
expire=self.timeout,
noreply=False)
if poked:
return True
LOG.warning("Unable to heartbeat by updating key '%s' with "
"extended expiry of %s seconds", self.name,
self.timeout)
return False
@_translate_failures
def get_owner(self):
return self.coord.client.get(self.name)
@property
def acquired(self):
return self in self.coord._acquired_locks
[docs]class MemcachedDriver(coordination.CoordinationDriverCachedRunWatchers,
coordination.CoordinationDriverWithExecutor):
"""A `memcached`_ based driver.
This driver users `memcached`_ concepts to provide the coordination driver
semantics and required API(s). It **is** fully functional and implements
all of the coordination driver API(s). It stores data into memcache
using expiries and `msgpack`_ encoded values.
The Memcached driver connection URI should look like::
memcached://[HOST[:PORT]][?OPTION1=VALUE1[&OPTION2=VALUE2[&...]]]
If not specified, HOST defaults to localhost and PORT defaults to 11211.
Available options are:
================== =======
Name Default
================== =======
timeout 30
membership_timeout 30
lock_timeout 30
leader_timeout 30
max_pool_size None
================== =======
General recommendations/usage considerations:
- Memcache (without different backend technology) is a **cache** enough
said.
.. _memcached: http://memcached.org/
.. _msgpack: http://msgpack.org/
"""
CHARACTERISTICS = (
coordination.Characteristics.DISTRIBUTED_ACROSS_THREADS,
coordination.Characteristics.DISTRIBUTED_ACROSS_PROCESSES,
coordination.Characteristics.DISTRIBUTED_ACROSS_HOSTS,
coordination.Characteristics.CAUSAL,
)
"""
Tuple of :py:class:`~tooz.coordination.Characteristics` introspectable
enum member(s) that can be used to interogate how this driver works.
"""
#: Key prefix attached to groups (used in name-spacing keys)
GROUP_PREFIX = b'_TOOZ_GROUP_'
#: Key prefix attached to leaders of groups (used in name-spacing keys)
GROUP_LEADER_PREFIX = b'_TOOZ_GROUP_LEADER_'
#: Key prefix attached to members of groups (used in name-spacing keys)
MEMBER_PREFIX = b'_TOOZ_MEMBER_'
#: Key where all groups 'known' are stored.
GROUP_LIST_KEY = b'_TOOZ_GROUP_LIST'
#: Default socket/lock/member/leader timeout used when none is provided.
DEFAULT_TIMEOUT = 30
#: String used to keep a key/member alive (until it next expires).
STILL_ALIVE = b"It's alive!"
[docs] def __init__(self, member_id, parsed_url, options):
super(MemcachedDriver, self).__init__(member_id, parsed_url, options)
self.host = (parsed_url.hostname or "localhost",
parsed_url.port or 11211)
default_timeout = self._options.get('timeout', self.DEFAULT_TIMEOUT)
self.timeout = int(default_timeout)
self.membership_timeout = int(self._options.get(
'membership_timeout', default_timeout))
self.lock_timeout = int(self._options.get(
'lock_timeout', default_timeout))
self.leader_timeout = int(self._options.get(
'leader_timeout', default_timeout))
max_pool_size = self._options.get('max_pool_size', None)
if max_pool_size is not None:
self.max_pool_size = int(max_pool_size)
else:
self.max_pool_size = None
self._acquired_locks = []
@staticmethod
def _msgpack_serializer(key, value):
if isinstance(value, bytes):
return value, 1
return utils.dumps(value), 2
@staticmethod
def _msgpack_deserializer(key, value, flags):
if flags == 1:
return value
if flags == 2:
return utils.loads(value)
raise coordination.SerializationError("Unknown serialization"
" format '%s'" % flags)
@_translate_failures
def _start(self):
super(MemcachedDriver, self)._start()
self.client = pymemcache_client.PooledClient(
self.host,
serializer=self._msgpack_serializer,
deserializer=self._msgpack_deserializer,
timeout=self.timeout,
connect_timeout=self.timeout,
max_pool_size=self.max_pool_size)
# Run heartbeat here because pymemcache use a lazy connection
# method and only connect once you do an operation.
self.heartbeat()
@_translate_failures
def _stop(self):
super(MemcachedDriver, self)._stop()
for lock in list(self._acquired_locks):
lock.release()
self.client.delete(self._encode_member_id(self._member_id))
self.client.close()
def _encode_group_id(self, group_id):
return self.GROUP_PREFIX + utils.to_binary(group_id)
def _encode_member_id(self, member_id):
return self.MEMBER_PREFIX + utils.to_binary(member_id)
def _encode_group_leader(self, group_id):
return self.GROUP_LEADER_PREFIX + utils.to_binary(group_id)
@_retry.retry()
def _add_group_to_group_list(self, group_id):
"""Add group to the group list.
:param group_id: The group id
"""
group_list, cas = self.client.gets(self.GROUP_LIST_KEY)
if cas:
group_list = set(group_list)
group_list.add(group_id)
if not self.client.cas(self.GROUP_LIST_KEY,
list(group_list), cas):
# Someone updated the group list before us, try again!
raise _retry.TryAgain
else:
if not self.client.add(self.GROUP_LIST_KEY,
[group_id], noreply=False):
# Someone updated the group list before us, try again!
raise _retry.TryAgain
@_retry.retry()
def _remove_from_group_list(self, group_id):
"""Remove group from the group list.
:param group_id: The group id
"""
group_list, cas = self.client.gets(self.GROUP_LIST_KEY)
group_list = set(group_list)
group_list.remove(group_id)
if not self.client.cas(self.GROUP_LIST_KEY,
list(group_list), cas):
# Someone updated the group list before us, try again!
raise _retry.TryAgain
[docs] def create_group(self, group_id):
encoded_group = self._encode_group_id(group_id)
@_translate_failures
def _create_group():
if not self.client.add(encoded_group, {}, noreply=False):
raise coordination.GroupAlreadyExist(group_id)
self._add_group_to_group_list(group_id)
return MemcachedFutureResult(self._executor.submit(_create_group))
[docs] def get_groups(self):
@_translate_failures
def _get_groups():
return self.client.get(self.GROUP_LIST_KEY) or []
return MemcachedFutureResult(self._executor.submit(_get_groups))
[docs] def join_group(self, group_id, capabilities=b""):
encoded_group = self._encode_group_id(group_id)
@_retry.retry()
@_translate_failures
def _join_group():
group_members, cas = self.client.gets(encoded_group)
if group_members is None:
raise coordination.GroupNotCreated(group_id)
if self._member_id in group_members:
raise coordination.MemberAlreadyExist(group_id,
self._member_id)
group_members[self._member_id] = {
b"capabilities": capabilities,
}
if not self.client.cas(encoded_group, group_members, cas):
# It changed, let's try again
raise _retry.TryAgain
self._joined_groups.add(group_id)
return MemcachedFutureResult(self._executor.submit(_join_group))
[docs] def leave_group(self, group_id):
encoded_group = self._encode_group_id(group_id)
@_retry.retry()
@_translate_failures
def _leave_group():
group_members, cas = self.client.gets(encoded_group)
if group_members is None:
raise coordination.GroupNotCreated(group_id)
if self._member_id not in group_members:
raise coordination.MemberNotJoined(group_id, self._member_id)
del group_members[self._member_id]
if not self.client.cas(encoded_group, group_members, cas):
# It changed, let's try again
raise _retry.TryAgain
self._joined_groups.discard(group_id)
return MemcachedFutureResult(self._executor.submit(_leave_group))
def _destroy_group(self, group_id):
self.client.delete(self._encode_group_id(group_id))
[docs] def delete_group(self, group_id):
encoded_group = self._encode_group_id(group_id)
@_retry.retry()
@_translate_failures
def _delete_group():
group_members, cas = self.client.gets(encoded_group)
if group_members is None:
raise coordination.GroupNotCreated(group_id)
if group_members != {}:
raise coordination.GroupNotEmpty(group_id)
# Delete is not atomic, so we first set the group to
# using CAS, and then we delete it, to avoid race conditions.
if not self.client.cas(encoded_group, None, cas):
raise _retry.TryAgain
self.client.delete(encoded_group)
self._remove_from_group_list(group_id)
return MemcachedFutureResult(self._executor.submit(_delete_group))
@_retry.retry()
@_translate_failures
def _get_members(self, group_id):
encoded_group = self._encode_group_id(group_id)
group_members, cas = self.client.gets(encoded_group)
if group_members is None:
raise coordination.GroupNotCreated(group_id)
actual_group_members = {}
for m, v in group_members.items():
# Never kick self from the group, we know we're alive
if (m == self._member_id or
self.client.get(self._encode_member_id(m))):
actual_group_members[m] = v
if group_members != actual_group_members:
# There are some dead members, update the group
if not self.client.cas(encoded_group, actual_group_members, cas):
# It changed, let's try again
raise _retry.TryAgain
return actual_group_members
[docs] def get_members(self, group_id):
def _get_members():
return set(self._get_members(group_id).keys())
return MemcachedFutureResult(self._executor.submit(_get_members))
[docs] def get_member_capabilities(self, group_id, member_id):
def _get_member_capabilities():
group_members = self._get_members(group_id)
if member_id not in group_members:
raise coordination.MemberNotJoined(group_id, member_id)
return group_members[member_id][b'capabilities']
return MemcachedFutureResult(
self._executor.submit(_get_member_capabilities))
[docs] def update_capabilities(self, group_id, capabilities):
encoded_group = self._encode_group_id(group_id)
@_retry.retry()
@_translate_failures
def _update_capabilities():
group_members, cas = self.client.gets(encoded_group)
if group_members is None:
raise coordination.GroupNotCreated(group_id)
if self._member_id not in group_members:
raise coordination.MemberNotJoined(group_id, self._member_id)
group_members[self._member_id][b'capabilities'] = capabilities
if not self.client.cas(encoded_group, group_members, cas):
# It changed, try again
raise _retry.TryAgain
return MemcachedFutureResult(
self._executor.submit(_update_capabilities))
[docs] def get_leader(self, group_id):
def _get_leader():
return self._get_leader_lock(group_id).get_owner()
return MemcachedFutureResult(self._executor.submit(_get_leader))
[docs] @_translate_failures
def heartbeat(self):
self.client.set(self._encode_member_id(self._member_id),
self.STILL_ALIVE,
expire=self.membership_timeout)
# Reset the acquired locks
for lock in self._acquired_locks:
lock.heartbeat()
return min(self.membership_timeout,
self.leader_timeout,
self.lock_timeout)
[docs] def get_lock(self, name):
return MemcachedLock(self, name, self.lock_timeout)
def _get_leader_lock(self, group_id):
return MemcachedLock(self, self._encode_group_leader(group_id),
self.leader_timeout)
[docs] @_translate_failures
def run_elect_coordinator(self):
for group_id, hooks in self._hooks_elected_leader.items():
# Try to grab the lock, if that fails, that means someone has it
# already.
leader_lock = self._get_leader_lock(group_id)
if leader_lock.acquire(blocking=False):
# We got the lock
hooks.run(coordination.LeaderElected(
group_id,
self._member_id))
[docs] def run_watchers(self, timeout=None):
result = super(MemcachedDriver, self).run_watchers(timeout=timeout)
self.run_elect_coordinator()
return result
MemcachedFutureResult = functools.partial(
coordination.CoordinatorResult,
failure_translator=_failure_translator)
