754 lines
25 KiB
Python
754 lines
25 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Copyright (C) 2016 Red Hat, Inc.
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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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import enum
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import logging
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import threading
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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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LOG = logging.getLogger(__name__)
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TOOZ_BACKENDS_NAMESPACE = "tooz.backends"
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class Characteristics(enum.Enum):
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"""Attempts to describe the characteristic that a driver supports."""
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DISTRIBUTED_ACROSS_THREADS = 'DISTRIBUTED_ACROSS_THREADS'
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"""Coordinator components when used by multiple **threads** work
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the same as if those components were only used by a single thread."""
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DISTRIBUTED_ACROSS_PROCESSES = 'DISTRIBUTED_ACROSS_PROCESSES'
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"""Coordinator components when used by multiple **processes** work
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the same as if those components were only used by a single thread."""
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DISTRIBUTED_ACROSS_HOSTS = 'DISTRIBUTED_ACROSS_HOSTS'
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"""Coordinator components when used by multiple **hosts** work
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the same as if those components were only used by a single thread."""
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LINEARIZABLE = 'LINEARIZABLE'
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"""The driver has the following properties:
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* Ensures each operation must take place before its
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completion time.
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* Any operation invoked subsequently must take place
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after the invocation and by extension, after the original operation
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itself.
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"""
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SEQUENTIAL = 'SEQUENTIAL'
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"""The driver has the following properties:
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* Operations can take effect before or after completion – but all
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operations retain the constraint that operations from any given process
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must take place in that processes order.
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"""
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CAUSAL = 'CAUSAL'
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"""The driver has the following properties:
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* Does **not** have to enforce the order of every
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operation from a process, perhaps, only causally related operations
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must occur in order.
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"""
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SERIALIZABLE = 'SERIALIZABLE'
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"""The driver has the following properties:
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* The history of **all** operations is equivalent to
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one that took place in some single atomic order but with unknown
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invocation and completion times - it places no bounds on
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time or order.
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"""
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SAME_VIEW_UNDER_PARTITIONS = 'SAME_VIEW_UNDER_PARTITIONS'
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"""When a client is connected to a server and that server is partitioned
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from a group of other servers it will (somehow) have the same view of
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data as a client connected to a server on the other side of the
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partition (typically this is accomplished by write availability being
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lost and therefore nothing can change).
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"""
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SAME_VIEW_ACROSS_CLIENTS = 'SAME_VIEW_ACROSS_CLIENTS'
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"""A client connected to one server will *always* have the same view
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every other client will have (no matter what server those other
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clients are connected to). Typically this is a sacrifice in
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write availability because before a write can be acknowledged it must
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be acknowledged by *all* servers in a cluster (so that all clients
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that are connected to those servers read the exact *same* thing).
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"""
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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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class Heart(object):
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"""Coordination drivers main liveness pump (its heart)."""
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def __init__(self, driver, thread_cls=threading.Thread,
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event_cls=threading.Event):
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self._thread_cls = thread_cls
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self._dead = event_cls()
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self._finished = event_cls()
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self._finished.set()
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self._runner = None
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self._driver = driver
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self._beats = 0
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@property
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def beats(self):
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"""How many times the heart has beaten."""
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return self._beats
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def is_alive(self):
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"""Returns if the heart is beating."""
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return not (self._runner is None
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or not self._runner.is_alive()
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or self._finished.is_set())
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@excutils.forever_retry_uncaught_exceptions
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def _beat_forever_until_stopped(self):
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"""Inner beating loop."""
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try:
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while not self._dead.is_set():
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with timeutils.StopWatch() as w:
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wait_until_next_beat = self._driver.heartbeat()
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ran_for = w.elapsed()
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if ran_for > wait_until_next_beat:
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LOG.warning(
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"Heartbeating took too long to execute (it ran for"
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" %0.2f seconds which is %0.2f seconds longer than"
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" the next heartbeat idle time). This may cause"
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" timeouts (in locks, leadership, ...) to"
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" happen (which will not end well).", ran_for,
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ran_for - wait_until_next_beat)
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self._beats += 1
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# NOTE(harlowja): use the event object for waiting and
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# not a sleep function since doing that will allow this code
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# to terminate early if stopped via the stop() method vs
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# having to wait until the sleep function returns.
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self._dead.wait(wait_until_next_beat)
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finally:
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self._finished.set()
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def start(self, thread_cls=None):
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"""Starts the heart beating thread (noop if already started)."""
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if not self.is_alive():
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self._finished.clear()
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self._dead.clear()
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self._beats = 0
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if thread_cls is None:
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thread_cls = self._thread_cls
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self._runner = thread_cls(target=self._beat_forever_until_stopped)
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self._runner.daemon = True
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self._runner.start()
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def stop(self):
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"""Requests the heart beating thread to stop beating."""
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self._dead.set()
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def wait(self, timeout=None):
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"""Wait up to given timeout for the heart beating thread to stop."""
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self._finished.wait(timeout)
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return self._finished.is_set()
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@six.add_metaclass(abc.ABCMeta)
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class CoordinationDriver(object):
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requires_beating = False
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"""
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Usage requirement that if true requires that the :py:meth:`~.heartbeat`
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be called periodically (at a given rate) to avoid locks, sessions and
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other from being automatically closed/discarded by the coordinators
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backing store.
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"""
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CHARACTERISTICS = ()
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"""
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Tuple of :py:class:`~tooz.coordination.Characteristics` introspectable
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enum member(s) that can be used to interogate how this driver works.
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"""
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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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self.requires_beating = (
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CoordinationDriver.heartbeat != self.__class__.heartbeat
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)
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self.heart = Heart(self)
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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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try:
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self._hooks_join_group[group_id].remove(callback)
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except ValueError:
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raise WatchCallbackNotFound(group_id, callback)
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if (not self._has_hooks_for_group(group_id) and
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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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try:
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self._hooks_leave_group[group_id].remove(callback)
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except ValueError:
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raise WatchCallbackNotFound(group_id, callback)
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if (not self._has_hooks_for_group(group_id) and
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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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try:
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self._hooks_elected_leader[group_id].remove(callback)
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except ValueError:
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raise WatchCallbackNotFound(group_id, 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, start_heart=False):
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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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if self.requires_beating and start_heart:
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self.heart.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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if self.heart.is_alive():
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self.heart.stop()
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self.heart.wait()
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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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: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 get_member_info(group_id, member_id):
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"""Return the statistics and 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 and statistics 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 member capabilities in the specified group.
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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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"""Update member status to indicate it is still alive.
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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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:return: The number of seconds to wait before sending a new heartbeat.
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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.
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Every call API 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:
|
||
try:
|
||
group_members_fut = self.get_members(group_id)
|
||
group_members = group_members_fut.get(
|
||
timeout=w.leftover(return_none=True))
|
||
except GroupNotCreated:
|
||
group_members = set()
|
||
else:
|
||
group_members = set(group_members)
|
||
if (group_id in self._joined_groups and
|
||
self._member_id not in group_members):
|
||
self._joined_groups.discard(group_id)
|
||
old_group_members = self._group_members.get(group_id, set())
|
||
for member_id in (group_members - old_group_members):
|
||
result.extend(
|
||
self._hooks_join_group[group_id].run(
|
||
MemberJoinedGroup(group_id, member_id)))
|
||
for member_id in (old_group_members - group_members):
|
||
result.extend(
|
||
self._hooks_leave_group[group_id].run(
|
||
MemberLeftGroup(group_id, member_id)))
|
||
self._group_members[group_id] = group_members
|
||
return result
|
||
|
||
|
||
def get_coordinator(backend_url, member_id,
|
||
characteristics=frozenset(), **kwargs):
|
||
"""Initialize and load the backend.
|
||
|
||
:param backend_url: the backend URL to use
|
||
:type backend: str
|
||
:param member_id: the id of the member
|
||
:type member_id: str
|
||
:param characteristics: set
|
||
:type characteristics: set of :py:class:`.Characteristics` that will
|
||
be matched to the requested driver (this **will**
|
||
become a **required** parameter in a future tooz
|
||
version)
|
||
:param kwargs: additional coordinator options (these take precedence over
|
||
options of the **same** name found in the ``backend_url``
|
||
arguments query string)
|
||
"""
|
||
parsed_url = netutils.urlsplit(backend_url)
|
||
parsed_qs = six.moves.urllib.parse.parse_qs(parsed_url.query)
|
||
if kwargs:
|
||
options = {}
|
||
for (k, v) in six.iteritems(kwargs):
|
||
options[k] = [v]
|
||
for (k, v) in six.iteritems(parsed_qs):
|
||
if k not in options:
|
||
options[k] = v
|
||
else:
|
||
options = parsed_qs
|
||
d = driver.DriverManager(
|
||
namespace=TOOZ_BACKENDS_NAMESPACE,
|
||
name=parsed_url.scheme,
|
||
invoke_on_load=True,
|
||
invoke_args=(member_id, parsed_url, options)).driver
|
||
characteristics = set(characteristics)
|
||
driver_characteristics = set(getattr(d, 'CHARACTERISTICS', set()))
|
||
missing_characteristics = characteristics - driver_characteristics
|
||
if missing_characteristics:
|
||
raise ToozDriverChosenPoorly("Desired characteristics %s"
|
||
" is not a strict subset of driver"
|
||
" characteristics %s, %s"
|
||
" characteristics were not found"
|
||
% (characteristics,
|
||
driver_characteristics,
|
||
missing_characteristics))
|
||
return d
|
||
|
||
|
||
class ToozError(Exception):
|
||
"""Exception raised when an internal error occurs.
|
||
|
||
Raised for instance in case of server internal error.
|
||
|
||
:ivar cause: the cause of the exception being raised, when not none this
|
||
will itself be an exception instance, this is useful for
|
||
creating a chain of exceptions for versions of python where
|
||
this is not yet implemented/supported natively.
|
||
|
||
"""
|
||
|
||
def __init__(self, message, cause=None):
|
||
super(ToozError, self).__init__(message)
|
||
self.cause = cause
|
||
|
||
|
||
class ToozDriverChosenPoorly(ToozError):
|
||
"""Raised when a driver does not match desired characteristics."""
|
||
|
||
|
||
class ToozConnectionError(ToozError):
|
||
"""Exception raised when the client cannot connect to the server."""
|
||
|
||
|
||
class OperationTimedOut(ToozError):
|
||
"""Exception raised when an operation times out."""
|
||
|
||
|
||
class LockAcquireFailed(ToozError):
|
||
"""Exception raised when a lock acquire fails in a context manager."""
|
||
|
||
|
||
class GroupNotCreated(ToozError):
|
||
"""Exception raised when the caller request an nonexistent group."""
|
||
def __init__(self, group_id):
|
||
self.group_id = group_id
|
||
super(GroupNotCreated, self).__init__(
|
||
"Group %s does not exist" % group_id)
|
||
|
||
|
||
class GroupAlreadyExist(ToozError):
|
||
"""Exception raised trying to create an already existing group."""
|
||
def __init__(self, group_id):
|
||
self.group_id = group_id
|
||
super(GroupAlreadyExist, self).__init__(
|
||
"Group %s already exists" % group_id)
|
||
|
||
|
||
class MemberAlreadyExist(ToozError):
|
||
"""Exception raised trying to join a group already joined."""
|
||
def __init__(self, group_id, member_id):
|
||
self.group_id = group_id
|
||
self.member_id = member_id
|
||
super(MemberAlreadyExist, self).__init__(
|
||
"Member %s has already joined %s" %
|
||
(member_id, group_id))
|
||
|
||
|
||
class MemberNotJoined(ToozError):
|
||
"""Exception raised trying to access a member not in a group."""
|
||
def __init__(self, group_id, member_id):
|
||
self.group_id = group_id
|
||
self.member_id = member_id
|
||
super(MemberNotJoined, self).__init__("Member %s has not joined %s" %
|
||
(member_id, group_id))
|
||
|
||
|
||
class GroupNotEmpty(ToozError):
|
||
"Exception raised when the caller try to delete a group with members."
|
||
def __init__(self, group_id):
|
||
self.group_id = group_id
|
||
super(GroupNotEmpty, self).__init__("Group %s is not empty" % group_id)
|
||
|
||
|
||
class WatchCallbackNotFound(ToozError):
|
||
"""Exception raised when unwatching a group.
|
||
|
||
Raised when the caller tries to unwatch a group with a callback that
|
||
does not exist.
|
||
|
||
"""
|
||
def __init__(self, group_id, callback):
|
||
self.group_id = group_id
|
||
self.callback = callback
|
||
super(WatchCallbackNotFound, self).__init__(
|
||
'Callback %s is not registered on group %s' %
|
||
(callback.__name__, group_id))
|
||
|
||
|
||
class SerializationError(ToozError):
|
||
"Exception raised when serialization or deserialization breaks."
|
||
|
||
|
||
def raise_with_cause(exc_cls, message, *args, **kwargs):
|
||
"""Helper to raise + chain exceptions (when able) and associate a *cause*.
|
||
|
||
**For internal usage only.**
|
||
|
||
NOTE(harlowja): Since in py3.x exceptions can be chained (due to
|
||
:pep:`3134`) we should try to raise the desired exception with the given
|
||
*cause*.
|
||
|
||
:param exc_cls: the :py:class:`~tooz.coordination.ToozError` class
|
||
to raise.
|
||
:param message: the text/str message that will be passed to
|
||
the exceptions constructor as its first positional
|
||
argument.
|
||
:param args: any additional positional arguments to pass to the
|
||
exceptions constructor.
|
||
:param kwargs: any additional keyword arguments to pass to the
|
||
exceptions constructor.
|
||
"""
|
||
if not issubclass(exc_cls, ToozError):
|
||
raise ValueError("Subclass of tooz error is required")
|
||
excutils.raise_with_cause(exc_cls, message, *args, **kwargs)
|