528 lines
17 KiB
Python
528 lines
17 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Copyright (C) 2013-2014 eNovance Inc. All Rights Reserved.
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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 abc
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import collections
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from oslo_utils import excutils
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from oslo_utils import netutils
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from oslo_utils import timeutils
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import six
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from stevedore import driver
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import tooz
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TOOZ_BACKENDS_NAMESPACE = "tooz.backends"
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class Hooks(list):
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def run(self, *args, **kwargs):
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return list(map(lambda cb: cb(*args, **kwargs), self))
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class Event(object):
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"""Base class for events."""
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class MemberJoinedGroup(Event):
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"""A member joined a group event."""
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def __init__(self, group_id, member_id):
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self.group_id = group_id
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self.member_id = member_id
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class MemberLeftGroup(Event):
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"""A member left a group event."""
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def __init__(self, group_id, member_id):
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self.group_id = group_id
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self.member_id = member_id
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class LeaderElected(Event):
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"""A leader as been elected."""
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def __init__(self, group_id, member_id):
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self.group_id = group_id
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self.member_id = member_id
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@six.add_metaclass(abc.ABCMeta)
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class CoordinationDriver(object):
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def __init__(self):
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self._started = False
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self._hooks_join_group = collections.defaultdict(Hooks)
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self._hooks_leave_group = collections.defaultdict(Hooks)
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self._hooks_elected_leader = collections.defaultdict(Hooks)
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# A cache for group members
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self._group_members = collections.defaultdict(set)
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def _has_hooks_for_group(self, group_id):
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return (len(self._hooks_join_group[group_id])
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+ len(self._hooks_leave_group[group_id]))
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@staticmethod
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def run_watchers(timeout=None):
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"""Run the watchers callback.
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This may also activate :py:meth:`.run_elect_coordinator` (depending
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on driver implementation).
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"""
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raise tooz.NotImplemented
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@staticmethod
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def run_elect_coordinator():
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"""Try to leader elect this coordinator & activate hooks on success."""
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raise tooz.NotImplemented
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@abc.abstractmethod
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def watch_join_group(self, group_id, callback):
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"""Call a function when group_id sees a new member joined.
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The callback functions will be executed when `run_watchers` is
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called.
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:param group_id: The group id to watch
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:param callback: The function to execute when a member joins this group
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"""
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self._hooks_join_group[group_id].append(callback)
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@abc.abstractmethod
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def unwatch_join_group(self, group_id, callback):
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"""Stop executing a function when a group_id sees a new member joined.
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:param group_id: The group id to unwatch
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:param callback: The function that was executed when a member joined
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this group
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"""
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self._hooks_join_group[group_id].remove(callback)
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if (not self._has_hooks_for_group(group_id)
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and group_id in self._group_members):
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del self._group_members[group_id]
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@abc.abstractmethod
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def watch_leave_group(self, group_id, callback):
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"""Call a function when group_id sees a new member leaving.
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The callback functions will be executed when `run_watchers` is
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called.
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:param group_id: The group id to watch
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:param callback: The function to execute when a member leaves this
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group
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"""
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self._hooks_leave_group[group_id].append(callback)
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@abc.abstractmethod
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def unwatch_leave_group(self, group_id, callback):
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"""Stop executing a function when a group_id sees a new member leaving.
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:param group_id: The group id to unwatch
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:param callback: The function that was executed when a member left
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this group
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"""
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self._hooks_leave_group[group_id].remove(callback)
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if (not self._has_hooks_for_group(group_id)
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and group_id in self._group_members):
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del self._group_members[group_id]
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@abc.abstractmethod
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def watch_elected_as_leader(self, group_id, callback):
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"""Call a function when member gets elected as leader.
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The callback functions will be executed when `run_watchers` is
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called.
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:param group_id: The group id to watch
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:param callback: The function to execute when a member leaves this
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group
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"""
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self._hooks_elected_leader[group_id].append(callback)
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@abc.abstractmethod
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def unwatch_elected_as_leader(self, group_id, callback):
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"""Call a function when member gets elected as leader.
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The callback functions will be executed when `run_watchers` is
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called.
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:param group_id: The group id to watch
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:param callback: The function to execute when a member leaves this
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group
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"""
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self._hooks_elected_leader[group_id].remove(callback)
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if not self._hooks_elected_leader[group_id]:
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del self._hooks_elected_leader[group_id]
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@staticmethod
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def stand_down_group_leader(group_id):
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"""Stand down as the group leader if we are.
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:param group_id: The group where we don't want to be a leader anymore
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"""
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raise tooz.NotImplemented
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@property
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def is_started(self):
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return self._started
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def start(self):
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"""Start the service engine.
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If needed, the establishment of a connection to the servers
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is initiated.
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"""
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if self._started:
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raise ToozError(
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"Can not start a driver which has not been stopped")
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self._start()
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self._started = True
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def _start(self):
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pass
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def stop(self):
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"""Stop the service engine.
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If needed, the connection to servers is closed and the client will
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disappear from all joined groups.
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"""
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if not self._started:
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raise ToozError("Can not stop a driver which has not been started")
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self._stop()
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self._started = False
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def _stop(self):
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pass
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@staticmethod
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def create_group(group_id):
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"""Request the creation of a group asynchronously.
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:param group_id: the id of the group to create
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:type group_id: str
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:returns: None
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def get_groups():
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"""Return the list composed by all groups ids asynchronously.
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:returns: the list of all created group ids
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def join_group(group_id, capabilities=b""):
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"""Join a group and establish group membership asynchronously.
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:param group_id: the id of the group to join
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:type group_id: str
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:param capabilities: the capabilities of the joined member
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:type capabilities: object (typically str)
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:returns: None
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def leave_group(group_id):
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"""Leave a group asynchronously.
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:param group_id: the id of the group to leave
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:type group_id: str
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:returns: None
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def delete_group(group_id):
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"""Delete a group asynchronously.
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:param group_id: the id of the group to leave
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:type group_id: str
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:returns: Result
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def get_members(group_id):
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"""Return the list of all members ids of the specified group
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asynchronously.
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:returns: list of all created group ids
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def get_member_capabilities(group_id, member_id):
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"""Return the capabilities of a member asynchronously.
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:param group_id: the id of the group of the member
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:type group_id: str
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:param member_id: the id of the member
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:type member_id: str
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:returns: capabilities of a member
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def update_capabilities(group_id, capabilities):
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"""Update capabilities of the caller in the specified group
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asynchronously.
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:param group_id: the id of the group of the current member
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:type group_id: str
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:param capabilities: the capabilities of the updated member
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:type capabilities: object (typically str)
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:returns: None
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def get_leader(group_id):
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"""Return the leader for a group.
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:param group_id: the id of the group:
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:returns: the leader
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:rtype: CoordAsyncResult
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"""
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raise tooz.NotImplemented
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@staticmethod
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def get_lock(name):
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"""Return a distributed lock.
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This is a exclusive lock, a second call to acquire() will block or
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return False.
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:param name: The lock name that is used to identify it across all
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nodes.
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"""
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raise tooz.NotImplemented
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@staticmethod
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def heartbeat():
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"""Method to run once in a while to be sure that the member is not dead
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and is still an active member of a group.
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"""
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pass
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@six.add_metaclass(abc.ABCMeta)
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class CoordAsyncResult(object):
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"""Representation of an asynchronous task, every call API
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returns an CoordAsyncResult object on which the result or
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the status of the task can be requested.
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"""
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@abc.abstractmethod
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def get(self, timeout=10):
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"""Retrieve the result of the corresponding asynchronous call.
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:param timeout: block until the timeout expire.
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:type timeout: float
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"""
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@abc.abstractmethod
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def done(self):
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"""Returns True if the task is done, False otherwise."""
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class _RunWatchersMixin(object):
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"""Mixin to share the *mostly* common ``run_watchers`` implementation."""
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def run_watchers(self, timeout=None):
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with timeutils.StopWatch(duration=timeout) as w:
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known_groups = self.get_groups().get(
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timeout=w.leftover(return_none=True))
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result = []
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for group_id in known_groups:
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try:
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group_members_fut = self.get_members(group_id)
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group_members = group_members_fut.get(
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timeout=w.leftover(return_none=True))
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except GroupNotCreated:
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group_members = set()
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else:
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group_members = set(group_members)
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if (group_id in self._joined_groups and
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self._member_id not in group_members):
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self._joined_groups.discard(group_id)
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old_group_members = self._group_members.get(group_id, set())
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for member_id in (group_members - old_group_members):
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result.extend(
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self._hooks_join_group[group_id].run(
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MemberJoinedGroup(group_id, member_id)))
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for member_id in (old_group_members - group_members):
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result.extend(
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self._hooks_leave_group[group_id].run(
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MemberLeftGroup(group_id, member_id)))
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self._group_members[group_id] = group_members
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return result
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def get_coordinator(backend_url, member_id, **kwargs):
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"""Initialize and load the backend.
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:param backend_url: the backend URL to use
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:type backend: str
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:param member_id: the id of the member
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:type member_id: str
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:param kwargs: additional coordinator options (these take precedence over
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options of the **same** name found in the ``backend_url``
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arguments query string)
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"""
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parsed_url = netutils.urlsplit(backend_url)
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parsed_qs = six.moves.urllib.parse.parse_qs(parsed_url.query)
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if kwargs:
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options = {}
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for (k, v) in six.iteritems(kwargs):
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options[k] = [v]
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for (k, v) in six.iteritems(parsed_qs):
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if k not in options:
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options[k] = v
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else:
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options = parsed_qs
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return driver.DriverManager(
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namespace=TOOZ_BACKENDS_NAMESPACE,
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name=parsed_url.scheme,
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invoke_on_load=True,
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invoke_args=(member_id, parsed_url, options)).driver
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class ToozError(Exception):
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"""Exception raised when an internal error occurs, for instance in
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case of server internal error.
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:ivar cause: the cause of the exception being raised, when not none this
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will itself be an exception instance, this is useful for
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creating a chain of exceptions for versions of python where
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this is not yet implemented/supported natively.
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"""
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def __init__(self, message, cause=None):
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super(ToozError, self).__init__(message)
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self.cause = cause
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class ToozConnectionError(ToozError):
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"""Exception raised when the client cannot manage to connect to the
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server.
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"""
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class OperationTimedOut(ToozError):
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"""Exception raised when an operation times out."""
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class LockAcquireFailed(ToozError):
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"""Exception raised when a lock acquire fails in a context manager."""
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class GroupNotCreated(ToozError):
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"""Exception raised when the caller request a group which does
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not exist.
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"""
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def __init__(self, group_id):
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self.group_id = group_id
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super(GroupNotCreated, self).__init__(
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"Group %s does not exist" % group_id)
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class GroupAlreadyExist(ToozError):
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"""Exception raised when the caller try to create a group which already
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exist.
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"""
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def __init__(self, group_id):
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self.group_id = group_id
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super(GroupAlreadyExist, self).__init__(
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"Group %s already exists" % group_id)
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class MemberAlreadyExist(ToozError):
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"""Exception raised when the caller try to join a group but a member
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with the same identifier belongs to that group.
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"""
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def __init__(self, group_id, member_id):
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self.group_id = group_id
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self.member_id = member_id
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super(MemberAlreadyExist, self).__init__(
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"Member %s has already joined %s" %
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(member_id, group_id))
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class MemberNotJoined(ToozError):
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"""Exception raised when the caller try to access a member which does not
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belongs to the specified group.
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"""
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def __init__(self, group_id, member_id):
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self.group_id = group_id
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self.member_id = member_id
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super(MemberNotJoined, self).__init__("Member %s has not joined %s" %
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(member_id, group_id))
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class GroupNotEmpty(ToozError):
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"Exception raised when the caller try to delete a group with members."
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def __init__(self, group_id):
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self.group_id = group_id
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super(GroupNotEmpty, self).__init__("Group %s is not empty" % group_id)
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class SerializationError(ToozError):
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"Exception raised when serialization or deserialization breaks."
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def raise_with_cause(exc_cls, message, *args, **kwargs):
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"""Helper to raise + chain exceptions (when able) and associate a *cause*.
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**For internal usage only.**
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NOTE(harlowja): Since in py3.x exceptions can be chained (due to
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:pep:`3134`) we should try to raise the desired exception with the given
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*cause*.
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:param exc_cls: the :py:class:`~tooz.coordination.ToozError` class
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to raise.
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:param message: the text/str message that will be passed to
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the exceptions constructor as its first positional
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argument.
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:param args: any additional positional arguments to pass to the
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exceptions constructor.
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:param kwargs: any additional keyword arguments to pass to the
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exceptions constructor.
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"""
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if not issubclass(exc_cls, ToozError):
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raise ValueError("Subclass of tooz error is required")
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excutils.raise_with_cause(exc_cls, message, *args, **kwargs)
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