vmware-nsx/quantum/openstack/common/lockutils.py
Nachi Ueno c9af623025 Import lockutils and fileutils from openstack-common
File lock function is needed to support iptables-based security group
implementation.

This is used by bp quantum-security-groups-iptables
Change-Id: Id9c116a1e10e5c240913fae7a127110b806eff0f
2012-11-08 14:31:44 -08:00

233 lines
8.3 KiB
Python

# vim: tabstop=4 shiftwidth=4 softtabstop=4
# Copyright 2011 OpenStack LLC.
# 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 quantum.openstack.common import cfg
from quantum.openstack.common import fileutils
from quantum.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',
default=os.path.abspath(os.path.join(os.path.dirname(__file__),
'../')),
help='Directory to use for lock files')
]
CONF = cfg.CONF
CONF.register_opts(util_opts)
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.
"""
def __init__(self, name):
self.lockfile = None
self.fname = name
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, 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
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)
def trylock(self):
raise NotImplementedError()
def unlock(self):
raise NotImplementedError()
class _WindowsLock(_InterProcessLock):
def trylock(self):
msvcrt.locking(self.lockfile, msvcrt.LK_NBLCK, 1)
def unlock(self):
msvcrt.locking(self.lockfile, msvcrt.LK_UNLCK, 1)
class _PosixLock(_InterProcessLock):
def trylock(self):
fcntl.lockf(self.lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)
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 bar 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.
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.
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.
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.
"""
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__})
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):
cleanup_dir = True
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:
# 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)
return retval
return inner
return wrap