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# -*- coding: utf-8 -*-
#
# Copyright © 2014 eNovance
#
# Author: Julien Danjou <julien@danjou.info>
#
# 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 hashlib
import six
import sysv_ipc
import tooz
from tooz import coordination
from tooz import locking
if sysv_ipc.KEY_MIN <= 0:
_KEY_RANGE = abs(sysv_ipc.KEY_MIN) + sysv_ipc.KEY_MAX
else:
_KEY_RANGE = sysv_ipc.KEY_MAX - sysv_ipc.KEY_MIN
class IPCLock(locking.Lock):
"""A sysv IPC based lock.
Please ensure you have read over (and understand) the limitations of sysv
IPC locks, and especially have tried and used $ ipcs -l (note the maximum
number of semaphores system wide field that command outputs). To ensure
that you do not reach that limit it is recommended to use destroy() at
the correct program exit/entry points.
"""
_LOCK_PROJECT = b'__TOOZ_LOCK_'
def __init__(self, name):
super(IPCLock, self).__init__(name)
self.key = self.ftok(name, self._LOCK_PROJECT)
self._lock = None
@staticmethod
def ftok(name, project):
# Similar to ftok & http://semanchuk.com/philip/sysv_ipc/#ftok_weakness
# but hopefully without as many weaknesses...
h = hashlib.md5()
if not isinstance(project, six.binary_type):
project = project.encode('ascii')
h.update(project)
if not isinstance(name, six.binary_type):
name = name.encode('ascii')
h.update(name)
return (int(h.hexdigest(), 16) % _KEY_RANGE) + sysv_ipc.KEY_MIN
def acquire(self, blocking=True):
if (blocking is not True
and sysv_ipc.SEMAPHORE_TIMEOUT_SUPPORTED is False):
raise tooz.NotImplemented(
"This system does not support semaphore timeout")
# Convert blocking argument to a valid timeout value
if blocking is True:
timeout = None
elif blocking is False:
timeout = 0
else:
timeout = blocking
while True:
try:
self._lock = sysv_ipc.Semaphore(self.key,
flags=sysv_ipc.IPC_CREX,
initial_value=1)
self._lock.undo = True
except sysv_ipc.ExistentialError:
# We failed to create it because it already exists, then try to
# grab the existing one.
try:
self._lock = sysv_ipc.Semaphore(self.key)
self._lock.undo = True
except sysv_ipc.ExistentialError:
# Semaphore has been deleted in the mean time, retry from
# the beginning!
continue
try:
self._lock.acquire(timeout=timeout)
except sysv_ipc.BusyError:
return False
except sysv_ipc.ExistentialError:
# Likely the lock has been deleted in the meantime, retry
continue
else:
return True
def release(self):
if self._lock is not None:
self._lock.remove()
self._lock = None
return True
return False
class IPCDriver(coordination.CoordinationDriver):
def __init__(self, member_id, parsed_url, options):
"""Initialize the IPC driver."""
super(IPCDriver, self).__init__()
@staticmethod
def get_lock(name):
return IPCLock(name)
@staticmethod
def watch_join_group(group_id, callback):
raise tooz.NotImplemented
@staticmethod
def unwatch_join_group(group_id, callback):
raise tooz.NotImplemented
@staticmethod
def watch_leave_group(group_id, callback):
raise tooz.NotImplemented
@staticmethod
def unwatch_leave_group(group_id, callback):
raise tooz.NotImplemented
@staticmethod
def watch_elected_as_leader(group_id, callback):
raise tooz.NotImplemented
@staticmethod
def unwatch_elected_as_leader(group_id, callback):
raise tooz.NotImplemented
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