OpenStack Block Storage (Cinder)
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# Copyright 2015 Intel
# All Rights Reserved.
#
# 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.
"""Coordination and locking utilities."""
import inspect
import uuid
import decorator
from oslo_config import cfg
from oslo_log import log
from oslo_utils import timeutils
from tooz import coordination
from cinder import exception
from cinder.i18n import _
LOG = log.getLogger(__name__)
coordination_opts = [
cfg.StrOpt('backend_url',
default='file://$state_path',
help='The backend URL to use for distributed coordination.'),
]
CONF = cfg.CONF
CONF.register_opts(coordination_opts, group='coordination')
class Coordinator(object):
"""Tooz coordination wrapper.
Coordination member id is created from concatenated
`prefix` and `agent_id` parameters.
:param str agent_id: Agent identifier
:param str prefix: Used to provide member identifier with a
meaningful prefix.
"""
def __init__(self, agent_id=None, prefix=''):
self.coordinator = None
self.agent_id = agent_id or str(uuid.uuid4())
self.started = False
self.prefix = prefix
def start(self):
if self.started:
return
# NOTE(bluex): Tooz expects member_id as a byte string.
member_id = (self.prefix + self.agent_id).encode('ascii')
self.coordinator = coordination.get_coordinator(
cfg.CONF.coordination.backend_url, member_id)
self.coordinator.start(start_heart=True)
self.started = True
def stop(self):
"""Disconnect from coordination backend and stop heartbeat."""
if self.started:
self.coordinator.stop()
self.coordinator = None
self.started = False
def get_lock(self, name):
"""Return a Tooz backend lock.
:param str name: The lock name that is used to identify it
across all nodes.
"""
# NOTE(bluex): Tooz expects lock name as a byte string.
lock_name = (self.prefix + name).encode('ascii')
if self.coordinator is not None:
return self.coordinator.get_lock(lock_name)
else:
raise exception.LockCreationFailed(_('Coordinator uninitialized.'))
COORDINATOR = Coordinator(prefix='cinder-')
def synchronized(lock_name, blocking=True, coordinator=COORDINATOR):
"""Synchronization decorator.
:param str lock_name: Lock name.
:param blocking: If True, blocks until the lock is acquired.
If False, raises exception when not acquired. Otherwise,
the value is used as a timeout value and if lock is not acquired
after this number of seconds exception is raised.
:param coordinator: Coordinator class to use when creating lock.
Defaults to the global coordinator.
:raises tooz.coordination.LockAcquireFailed: if lock is not acquired
Decorating a method like so::
@synchronized('mylock')
def foo(self, *args):
...
ensures that only one process will execute the foo method at a time.
Different methods can share the same lock::
@synchronized('mylock')
def foo(self, *args):
...
@synchronized('mylock')
def bar(self, *args):
...
This way only one of either foo or bar can be executing at a time.
Lock name can be formatted using Python format string syntax::
@synchronized('{f_name}-{vol.id}-{snap[name]}')
def foo(self, vol, snap):
...
Available field names are: decorated function parameters and
`f_name` as a decorated function name.
"""
@decorator.decorator
def _synchronized(f, *a, **k):
call_args = inspect.getcallargs(f, *a, **k)
call_args['f_name'] = f.__name__
lock = coordinator.get_lock(lock_name.format(**call_args))
t1 = timeutils.now()
t2 = None
try:
with lock(blocking):
t2 = timeutils.now()
LOG.debug('Lock "%(name)s" acquired by "%(function)s" :: '
'waited %(wait_secs)0.3fs',
{'name': lock.name,
'function': f.__name__,
'wait_secs': (t2 - t1)})
return f(*a, **k)
finally:
t3 = timeutils.now()
if t2 is None:
held_secs = "N/A"
else:
held_secs = "%0.3fs" % (t3 - t2)
LOG.debug('Lock "%(name)s" released by "%(function)s" :: held '
'%(held_secs)s',
{'name': lock.name,
'function': f.__name__,
'held_secs': held_secs})
return _synchronized