--- /dev/null
+# 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 cinder.openstack.common import cfg
+from cinder.openstack.common import fileutils
+from cinder.openstack.common.gettextutils import _
+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',
+ 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
Code Review / openstack-build / cinder-build.git / commitdiff