# tooz.drivers.ipc

# 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 struct
    import time

    import msgpack
    import sysv_ipc

    from oslo_utils.secretutils import md5

    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 = md5(usedforsecurity=False)
        if not isinstance(project, bytes):
            project = project.encode('ascii')
        h.update(project)
        if not isinstance(name, bytes):
            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

    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)

        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))

        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))

        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)

        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()

        def get_groups(self):
            return coordination.CoordinatorResult(self._executor.submit(
                self._get_groups_handler))

        @staticmethod
        def get_lock(name):
            return IPCLock(name)

this page last updated: 2022-01-12 20:19:17

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