Source code for tooz.drivers.ipc
# -*- 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 hashlib
import struct
import time
import msgpack
import six
import sysv_ipc
import tooz
from tooz import coordination
from tooz import locking
from tooz import utils
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
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
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 = ftok(name, self._LOCK_PROJECT)
self._lock = None
def break_(self):
try:
lock = sysv_ipc.Semaphore(key=self.key)
lock.remove()
except sysv_ipc.ExistentialError:
return False
else:
return True
def acquire(self, blocking=True, shared=False):
if shared:
raise tooz.NotImplemented
if (blocking is not True and
sysv_ipc.SEMAPHORE_TIMEOUT_SUPPORTED is False):
raise tooz.NotImplemented("This system does not support"
" semaphore timeouts")
blocking, timeout = utils.convert_blocking(blocking)
start_time = None
if not blocking:
timeout = 0
elif blocking and timeout is not None:
start_time = time.time()
while True:
tmplock = None
try:
tmplock = sysv_ipc.Semaphore(self.key,
flags=sysv_ipc.IPC_CREX,
initial_value=1)
tmplock.undo = True
except sysv_ipc.ExistentialError:
# We failed to create it because it already exists, then try to
# grab the existing one.
try:
tmplock = sysv_ipc.Semaphore(self.key)
tmplock.undo = True
except sysv_ipc.ExistentialError:
# Semaphore has been deleted in the mean time, retry from
# the beginning!
continue
if start_time is not None:
elapsed = max(0.0, time.time() - start_time)
if elapsed >= timeout:
# Ran out of time...
return False
adjusted_timeout = timeout - elapsed
else:
adjusted_timeout = timeout
try:
tmplock.acquire(timeout=adjusted_timeout)
except sysv_ipc.BusyError:
tmplock = None
return False
except sysv_ipc.ExistentialError:
# Likely the lock has been deleted in the meantime, retry
continue
else:
self._lock = tmplock
return True
def release(self):
if self._lock is not None:
try:
self._lock.remove()
self._lock = None
except sysv_ipc.ExistentialError:
return False
return True
return False
[docs]class IPCDriver(coordination.CoordinationDriverWithExecutor):
"""A `IPC`_ based driver.
This driver uses `IPC`_ concepts to provide the coordination driver
semantics and required API(s). It **is** missing some functionality but
in the future these not implemented API(s) will be filled in.
The IPC driver connection URI should look like::
ipc://
General recommendations/usage considerations:
- It is **not** distributed (or recommended to be used in those
situations, so the developer using this should really take that into
account when applying this driver in there app).
.. _IPC: http://en.wikipedia.org/wiki/Inter-process_communication
"""
CHARACTERISTICS = (
coordination.Characteristics.NON_TIMEOUT_BASED,
coordination.Characteristics.DISTRIBUTED_ACROSS_THREADS,
coordination.Characteristics.DISTRIBUTED_ACROSS_PROCESSES,
)
"""
Tuple of :py:class:`~tooz.coordination.Characteristics` introspectable
enum member(s) that can be used to interogate how this driver works.
"""
_SEGMENT_SIZE = 1024
_GROUP_LIST_KEY = "GROUP_LIST"
_GROUP_PROJECT = "_TOOZ_INTERNAL"
_INTERNAL_LOCK_NAME = "TOOZ_INTERNAL_LOCK"
def _start(self):
super(IPCDriver, self)._start()
self._group_list = sysv_ipc.SharedMemory(
ftok(self._GROUP_LIST_KEY, self._GROUP_PROJECT),
sysv_ipc.IPC_CREAT,
size=self._SEGMENT_SIZE)
self._lock = self.get_lock(self._INTERNAL_LOCK_NAME)
def _stop(self):
super(IPCDriver, self)._stop()
try:
self._group_list.detach()
self._group_list.remove()
except sysv_ipc.ExistentialError:
pass
def _read_group_list(self):
data = self._group_list.read(byte_count=2)
length = struct.unpack("H", data)[0]
if length == 0:
return set()
data = self._group_list.read(byte_count=length, offset=2)
return set(msgpack.loads(data))
def _write_group_list(self, group_list):
data = msgpack.dumps(list(group_list))
if len(data) >= self._SEGMENT_SIZE - 2:
raise tooz.ToozError("Group list is too big")
self._group_list.write(struct.pack('H', len(data)))
self._group_list.write(data, offset=2)
[docs] def create_group(self, group_id):
def _create_group():
with self._lock:
group_list = self._read_group_list()
if group_id in group_list:
raise coordination.GroupAlreadyExist(group_id)
group_list.add(group_id)
self._write_group_list(group_list)
return coordination.CoordinatorResult(
self._executor.submit(_create_group))
[docs] def delete_group(self, group_id):
def _delete_group():
with self._lock:
group_list = self._read_group_list()
if group_id not in group_list:
raise coordination.GroupNotCreated(group_id)
group_list.remove(group_id)
self._write_group_list(group_list)
return coordination.CoordinatorResult(
self._executor.submit(_delete_group))
[docs] def watch_join_group(self, group_id, callback):
# Check the group exist
self.get_members(group_id).get()
super(IPCDriver, self).watch_join_group(group_id, callback)
[docs] def watch_leave_group(self, group_id, callback):
# Check the group exist
self.get_members(group_id).get()
super(IPCDriver, self).watch_leave_group(group_id, callback)
def _get_groups_handler(self):
with self._lock:
return self._read_group_list()
[docs] def get_groups(self):
return coordination.CoordinatorResult(self._executor.submit(
self._get_groups_handler))
[docs] @staticmethod
def get_lock(name):
return IPCLock(name)
