146 lines
4.8 KiB
Python
146 lines
4.8 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Copyright © 2014 eNovance
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#
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# Author: Julien Danjou <julien@danjou.info>
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import hashlib
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import six
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import sysv_ipc
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import tooz
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from tooz import coordination
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from tooz import locking
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if sysv_ipc.KEY_MIN <= 0:
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_KEY_RANGE = abs(sysv_ipc.KEY_MIN) + sysv_ipc.KEY_MAX
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else:
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_KEY_RANGE = sysv_ipc.KEY_MAX - sysv_ipc.KEY_MIN
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class IPCLock(locking.Lock):
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"""A sysv IPC based lock.
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Please ensure you have read over (and understand) the limitations of sysv
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IPC locks, and especially have tried and used $ ipcs -l (note the maximum
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number of semaphores system wide field that command outputs). To ensure
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that you do not reach that limit it is recommended to use destroy() at
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the correct program exit/entry points.
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"""
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_LOCK_PROJECT = b'__TOOZ_LOCK_'
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def __init__(self, name, timeout):
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super(IPCLock, self).__init__(name)
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self.key = self.ftok(name, self._LOCK_PROJECT)
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try:
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self._lock = sysv_ipc.Semaphore(self.key,
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flags=sysv_ipc.IPC_CREX,
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initial_value=1)
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except sysv_ipc.ExistentialError:
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self._lock = sysv_ipc.Semaphore(self.key)
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self._lock.undo = True
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self.timeout = timeout
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@staticmethod
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def ftok(name, project):
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# Similar to ftok & http://semanchuk.com/philip/sysv_ipc/#ftok_weakness
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# but hopefully without as many weaknesses...
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h = hashlib.md5()
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if not isinstance(project, six.binary_type):
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project = project.encode('ascii')
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h.update(project)
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if not isinstance(name, six.binary_type):
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name = name.encode('ascii')
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h.update(name)
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return (int(h.hexdigest(), 16) % _KEY_RANGE) + sysv_ipc.KEY_MIN
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def acquire(self, blocking=True):
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timeout = self.timeout if blocking else 0
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try:
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self._lock.acquire(timeout=timeout)
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except (sysv_ipc.BusyError, sysv_ipc.ExistentialError):
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return False
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else:
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return True
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def release(self):
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try:
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self._lock.release()
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except sysv_ipc.ExistentialError:
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return False
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else:
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return True
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def destroy(self):
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"""This will destroy the lock.
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NOTE(harlowja): this will destroy the lock, and if it is being shared
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across processes this can have unintended consquences, so it *must*
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only be used when it is *safe* to remove it (ie at a known program
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exit point, where it can be ensured that no other process will be
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using it, or that if other processes are using it they can tolerate
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it being destroyed).
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Read your man pages for `semctl(IPC_RMID)` before using this to
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understand its side-effects on other programs that *may* be
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concurrently using the same lock while it is being destroyed...
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"""
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try:
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self._lock.remove()
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except sysv_ipc.ExistentialError:
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pass
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class IPCDriver(coordination.CoordinationDriver):
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def __init__(self, member_id, parsed_url, options):
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"""Initialize the IPC driver.
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:param lock_timeout: how many seconds to wait when trying to acquire
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a lock in blocking mode. None means forever, 0
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means don't wait, any other value means wait
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this amount of seconds.
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"""
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super(IPCDriver, self).__init__()
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self.lock_timeout = int(options.get('lock_timeout', ['30'])[-1])
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def get_lock(self, name):
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return IPCLock(name, self.lock_timeout)
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@staticmethod
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def watch_join_group(group_id, callback):
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raise tooz.NotImplemented
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@staticmethod
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def unwatch_join_group(group_id, callback):
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raise tooz.NotImplemented
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@staticmethod
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def watch_leave_group(group_id, callback):
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raise tooz.NotImplemented
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@staticmethod
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def unwatch_leave_group(group_id, callback):
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raise tooz.NotImplemented
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@staticmethod
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def watch_elected_as_leader(group_id, callback):
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raise tooz.NotImplemented
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@staticmethod
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def unwatch_elected_as_leader(group_id, callback):
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raise tooz.NotImplemented
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