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