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OpenStack Study: lockutils.py**** CubicPower OpenStack Study ****
# vim: tabstop=4 shiftwidth=4 softtabstop=4 # Copyright 2011 OpenStack Foundation. # 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. import errno import functools import os import shutil import tempfile import time import weakref from eventlet import semaphore from oslo.config import cfg from cinder.openstack.common import fileutils from cinder.openstack.common.gettextutils import _ from cinder.openstack.common import local from cinder.openstack.common import log as logging LOG = logging.getLogger(__name__) util_opts = [ cfg.BoolOpt('disable_process_locking', default=False, help='Whether to disable inter-process locks'), cfg.StrOpt('lock_path', help=('Directory to use for lock files. Default to a ' 'temp directory')) ] CONF = cfg.CONF CONF.register_opts(util_opts)
**** CubicPower OpenStack Study **** def set_defaults(lock_path): cfg.set_defaults(util_opts, lock_path=lock_path)
**** CubicPower OpenStack Study **** class _InterProcessLock(object): """Lock implementation which allows multiple locks, working around issues like bugs.debian.org/cgi-bin/bugreport.cgi?bug=632857 and does not require any cleanup. Since the lock is always held on a file descriptor rather than outside of the process, the lock gets dropped automatically if the process crashes, even if __exit__ is not executed. There are no guarantees regarding usage by multiple green threads in a single process here. This lock works only between processes. Exclusive access between local threads should be achieved using the semaphores in the @synchronized decorator. Note these locks are released when the descriptor is closed, so it's not safe to close the file descriptor while another green thread holds the lock. Just opening and closing the lock file can break synchronisation, so lock files must be accessed only using this abstraction. """
**** CubicPower OpenStack Study **** def __init__(self, name): self.lockfile = None self.fname = name
**** CubicPower OpenStack Study **** def __enter__(self): self.lockfile = open(self.fname, 'w') while True: try: # Using non-blocking locks since green threads are not # patched to deal with blocking locking calls. # Also upon reading the MSDN docs for locking(), it seems # to have a laughable 10 attempts "blocking" mechanism. self.trylock() return self except IOError as e: if e.errno in (errno.EACCES, errno.EAGAIN): # external locks synchronise things like iptables # updates - give it some time to prevent busy spinning time.sleep(0.01) else: raise
**** CubicPower OpenStack Study **** def __exit__(self, exc_type, exc_val, exc_tb): try: self.unlock() self.lockfile.close() except IOError: LOG.exception(_("Could not release the acquired lock `%s`"), self.fname)
**** CubicPower OpenStack Study **** def trylock(self): raise NotImplementedError()
**** CubicPower OpenStack Study **** def unlock(self): raise NotImplementedError()
**** CubicPower OpenStack Study **** class _WindowsLock(_InterProcessLock):
**** CubicPower OpenStack Study **** def trylock(self): msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_NBLCK, 1)
**** CubicPower OpenStack Study **** def unlock(self): msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_UNLCK, 1)
**** CubicPower OpenStack Study **** class _PosixLock(_InterProcessLock):
**** CubicPower OpenStack Study **** def trylock(self): fcntl.lockf(self.lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)
**** CubicPower OpenStack Study **** def unlock(self): fcntl.lockf(self.lockfile, fcntl.LOCK_UN) if os.name == 'nt': import msvcrt InterProcessLock = _WindowsLock else: import fcntl InterProcessLock = _PosixLock _semaphores = weakref.WeakValueDictionary() def synchronized(name, lock_file_prefix, external=False, lock_path=None): """Synchronization decorator. Decorating a method like so:: @synchronized('mylock') def foo(self, *args): ... ensures that only one thread 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. :param lock_file_prefix: The lock_file_prefix argument is used to provide lock files on disk with a meaningful prefix. The prefix should end with a hyphen ('-') if specified. :param external: The external keyword argument denotes whether this lock should work across multiple processes. This means that if two different workers both run a a method decorated with @synchronized('mylock', external=True), only one of them will execute at a time. :param lock_path: The lock_path keyword argument is used to specify a special location for external lock files to live. If nothing is set, then CONF.lock_path is used as a default. """
**** CubicPower OpenStack Study **** def foo(self, *args): ... ensures that only one thread will execute the foo method at a time. Different methods can share the same lock:: @synchronized('mylock')
**** CubicPower OpenStack Study **** def foo(self, *args): ... @synchronized('mylock')
**** CubicPower OpenStack Study **** def bar(self, *args): ... This way only one of either foo or bar can be executing at a time. :param lock_file_prefix: The lock_file_prefix argument is used to provide lock files on disk with a meaningful prefix. The prefix should end with a hyphen ('-') if specified. :param external: The external keyword argument denotes whether this lock should work across multiple processes. This means that if two different workers both run a a method decorated with @synchronized('mylock', external=True), only one of them will execute at a time. :param lock_path: The lock_path keyword argument is used to specify a special location for external lock files to live. If nothing is set, then CONF.lock_path is used as a default. """
**** CubicPower OpenStack Study **** def wrap(f): @functools.wraps(f) def inner(*args, **kwargs): # NOTE(soren): If we ever go natively threaded, this will be racy. # See http://stackoverflow.com/questions/5390569/dyn # amically-allocating-and-destroying-mutexes sem = _semaphores.get(name, semaphore.Semaphore()) if name not in _semaphores: # this check is not racy - we're already holding ref locally # so GC won't remove the item and there was no IO switch # (only valid in greenthreads) _semaphores[name] = sem with sem: LOG.debug(_('Got semaphore "%(lock)s" for method ' '"%(method)s"...'), {'lock': name, 'method': f.__name__}) # NOTE(mikal): I know this looks odd if not hasattr(local.strong_store, 'locks_held'): local.strong_store.locks_held = [] local.strong_store.locks_held.append(name) try: if external and not CONF.disable_process_locking: LOG.debug(_('Attempting to grab file lock "%(lock)s" ' 'for method "%(method)s"...'), {'lock': name, 'method': f.__name__}) cleanup_dir = False # We need a copy of lock_path because it is non-local local_lock_path = lock_path if not local_lock_path: local_lock_path = CONF.lock_path if not local_lock_path: cleanup_dir = True local_lock_path = tempfile.mkdtemp() if not os.path.exists(local_lock_path): fileutils.ensure_tree(local_lock_path) # NOTE(mikal): the lock name cannot contain directory # separators safe_name = name.replace(os.sep, '_') lock_file_name = '%s%s' % (lock_file_prefix, safe_name) lock_file_path = os.path.join(local_lock_path, lock_file_name) try: lock = InterProcessLock(lock_file_path) with lock: LOG.debug(_('Got file lock "%(lock)s" at ' '%(path)s for method ' '"%(method)s"...'), {'lock': name, 'path': lock_file_path, 'method': f.__name__}) retval = f(*args, **kwargs) finally: LOG.debug(_('Released file lock "%(lock)s" at ' '%(path)s for method "%(method)s"...'), {'lock': name, 'path': lock_file_path, 'method': f.__name__}) # NOTE(vish): This removes the tempdir if we needed # to create one. This is used to # cleanup the locks left behind by unit # tests. if cleanup_dir: shutil.rmtree(local_lock_path) else: retval = f(*args, **kwargs) finally: local.strong_store.locks_held.remove(name) return retval return inner return wrap def synchronized_with_prefix(lock_file_prefix): """Partial object generator for the synchronization decorator. Redefine @synchronized in each project like so:: (in nova/utils.py) from nova.openstack.common import lockutils synchronized = lockutils.synchronized_with_prefix('nova-') (in nova/foo.py) from nova import utils @utils.synchronized('mylock') def bar(self, *args): ... The lock_file_prefix argument is used to provide lock files on disk with a meaningful prefix. The prefix should end with a hyphen ('-') if specified. """ return functools.partial(synchronized, lock_file_prefix=lock_file_prefix)
**** CubicPower OpenStack Study **** def inner(*args, **kwargs): # NOTE(soren): If we ever go natively threaded, this will be racy. # See http://stackoverflow.com/questions/5390569/dyn # amically-allocating-and-destroying-mutexes sem = _semaphores.get(name, semaphore.Semaphore()) if name not in _semaphores: # this check is not racy - we're already holding ref locally # so GC won't remove the item and there was no IO switch # (only valid in greenthreads) _semaphores[name] = sem with sem: LOG.debug(_('Got semaphore "%(lock)s" for method ' '"%(method)s"...'), {'lock': name, 'method': f.__name__}) # NOTE(mikal): I know this looks odd if not hasattr(local.strong_store, 'locks_held'): local.strong_store.locks_held = [] local.strong_store.locks_held.append(name) try: if external and not CONF.disable_process_locking: LOG.debug(_('Attempting to grab file lock "%(lock)s" ' 'for method "%(method)s"...'), {'lock': name, 'method': f.__name__}) cleanup_dir = False # We need a copy of lock_path because it is non-local local_lock_path = lock_path if not local_lock_path: local_lock_path = CONF.lock_path if not local_lock_path: cleanup_dir = True local_lock_path = tempfile.mkdtemp() if not os.path.exists(local_lock_path): fileutils.ensure_tree(local_lock_path) # NOTE(mikal): the lock name cannot contain directory # separators safe_name = name.replace(os.sep, '_') lock_file_name = '%s%s' % (lock_file_prefix, safe_name) lock_file_path = os.path.join(local_lock_path, lock_file_name) try: lock = InterProcessLock(lock_file_path) with lock: LOG.debug(_('Got file lock "%(lock)s" at ' '%(path)s for method ' '"%(method)s"...'), {'lock': name, 'path': lock_file_path, 'method': f.__name__}) retval = f(*args, **kwargs) finally: LOG.debug(_('Released file lock "%(lock)s" at ' '%(path)s for method "%(method)s"...'), {'lock': name, 'path': lock_file_path, 'method': f.__name__}) # NOTE(vish): This removes the tempdir if we needed # to create one. This is used to # cleanup the locks left behind by unit # tests. if cleanup_dir: shutil.rmtree(local_lock_path) else: retval = f(*args, **kwargs) finally: local.strong_store.locks_held.remove(name) return retval return inner return wrap def synchronized_with_prefix(lock_file_prefix): """Partial object generator for the synchronization decorator. Redefine @synchronized in each project like so:: (in nova/utils.py) from nova.openstack.common import lockutils synchronized = lockutils.synchronized_with_prefix('nova-') (in nova/foo.py) from nova import utils @utils.synchronized('mylock')
**** CubicPower OpenStack Study **** def bar(self, *args): ... The lock_file_prefix argument is used to provide lock files on disk with a meaningful prefix. The prefix should end with a hyphen ('-') if specified. """ return functools.partial(synchronized, lock_file_prefix=lock_file_prefix)
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