# -*- coding: utf-8 -*-
# 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 logging
import os
import threading
import time
import six
from fasteners import _utils
LOG = logging.getLogger(__name__)
def _ensure_tree(path):
"""Create a directory (and any ancestor directories required).
:param path: Directory to create
"""
try:
os.makedirs(path)
except OSError as e:
if e.errno == errno.EEXIST:
if not os.path.isdir(path):
raise
else:
return False
elif e.errno == errno.EISDIR:
return False
else:
raise
else:
return True
class _InterProcessLock(object):
"""An interprocess locking implementation.
This is a lock implementation which allows multiple locks, working around
issues like http://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 threads in a
single process here. This lock works only between processes.
Note these locks are released when the descriptor is closed, so it's not
safe to close the file descriptor while another thread holds the
lock. Just opening and closing the lock file can break synchronization,
so lock files must be accessed only using this abstraction.
.. warning::
It is quite useful to read before using (to understand
the risks involved): http://0pointer.de/blog/projects/locking.html
"""
MAX_DELAY = 0.1
"""
Default maximum delay we will wait to try to acquire the lock (when
it's busy/being held by another process).
"""
DELAY_INCREMENT = 0.01
"""
Default increment we will use (up to max delay) after each attempt before
next attempt to acquire the lock. For example if 3 attempts have been made
the calling thread will sleep (0.01 * 3) before the next attempt to
acquire the lock (and repeat).
"""
def __init__(self, path, sleep_func=time.sleep, logger=None):
self.lockfile = None
self.path = _utils.canonicalize_path(path)
self.acquired = False
self.sleep_func = sleep_func
self.logger = _utils.pick_first_not_none(logger, LOG)
def _try_acquire(self, blocking, watch):
try:
self.trylock()
except IOError as e:
if e.errno in (errno.EACCES, errno.EAGAIN):
if not blocking or watch.expired():
return False
else:
raise _utils.RetryAgain()
else:
raise threading.ThreadError("Unable to acquire lock on"
" `%(path)s` due to"
" %(exception)s" %
{
'path': self.path,
'exception': e,
})
else:
return True
def _do_open(self):
basedir = os.path.dirname(self.path)
if basedir:
made_basedir = _ensure_tree(basedir)
if made_basedir:
self.logger.log(_utils.BLATHER,
'Created lock base path `%s`', basedir)
# Open in append mode so we don't overwrite any potential contents of
# the target file. This eliminates the possibility of an attacker
# creating a symlink to an important file in our lock path.
if self.lockfile is None or self.lockfile.closed:
self.lockfile = open(self.path, 'a')
def acquire(self, blocking=True,
delay=DELAY_INCREMENT, max_delay=MAX_DELAY,
timeout=None):
"""Attempt to acquire the given lock.
:param blocking: whether to wait forever to try to acquire the lock
:type blocking: bool
:param delay: when blocking this is the delay time in seconds that
will be added after each failed acquisition
:type delay: int/float
:param max_delay: the maximum delay to have (this limits the
accumulated delay(s) added after each failed
acquisition)
:type max_delay: int/float
:param timeout: an optional timeout (limits how long blocking
will occur for)
:type timeout: int/float
:returns: whether or not the acquisition succeeded
:rtype: bool
"""
if delay < 0:
raise ValueError("Delay must be greater than or equal to zero")
if timeout is not None and timeout < 0:
raise ValueError("Timeout must be greater than or equal to zero")
if delay >= max_delay:
max_delay = delay
self._do_open()
watch = _utils.StopWatch(duration=timeout)
r = _utils.Retry(delay, max_delay,
sleep_func=self.sleep_func, watch=watch)
with watch:
gotten = r(self._try_acquire, blocking, watch)
if not gotten:
self.acquired = False
return False
else:
self.acquired = True
self.logger.log(_utils.BLATHER,
"Acquired file lock `%s` after waiting %0.3fs [%s"
" attempts were required]", self.path,
watch.elapsed(), r.attempts)
return True
def _do_close(self):
if self.lockfile is not None:
self.lockfile.close()
self.lockfile = None
def __enter__(self):
gotten = self.acquire()
if not gotten:
# This shouldn't happen, but just incase...
raise threading.ThreadError("Unable to acquire a file lock"
" on `%s` (when used as a"
" context manager)" % self.path)
return self
def release(self):
"""Release the previously acquired lock."""
if not self.acquired:
raise threading.ThreadError("Unable to release an unacquired"
" lock")
try:
self.unlock()
except IOError:
self.logger.exception("Could not unlock the acquired lock opened"
" on `%s`", self.path)
else:
self.acquired = False
try:
self._do_close()
except IOError:
self.logger.exception("Could not close the file handle"
" opened on `%s`", self.path)
else:
self.logger.log(_utils.BLATHER,
"Unlocked and closed file lock open on"
" `%s`", self.path)
def __exit__(self, exc_type, exc_val, exc_tb):
self.release()
def exists(self):
"""Checks if the path that this lock exists at actually exists."""
return os.path.exists(self.path)
def trylock(self):
self._trylock(self.lockfile)
def unlock(self):
self._unlock(self.lockfile)
@staticmethod
def _trylock():
raise NotImplementedError()
@staticmethod
def _unlock():
raise NotImplementedError()
class _WindowsLock(_InterProcessLock):
"""Interprocess lock implementation that works on windows systems."""
@staticmethod
def _trylock(lockfile):
fileno = lockfile.fileno()
msvcrt.locking(fileno, msvcrt.LK_NBLCK, 1)
@staticmethod
def _unlock(lockfile):
fileno = lockfile.fileno()
msvcrt.locking(fileno, msvcrt.LK_UNLCK, 1)
class _FcntlLock(_InterProcessLock):
"""Interprocess lock implementation that works on posix systems."""
@staticmethod
def _trylock(lockfile):
fcntl.lockf(lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)
@staticmethod
def _unlock(lockfile):
fcntl.lockf(lockfile, fcntl.LOCK_UN)
if os.name == 'nt':
import msvcrt
InterProcessLock = _WindowsLock
else:
import fcntl
InterProcessLock = _FcntlLock
def interprocess_locked(path):
"""Acquires & releases a interprocess lock around call into
decorated function."""
lock = InterProcessLock(path)
def decorator(f):
@six.wraps(f)
def wrapper(*args, **kwargs):
with lock:
return f(*args, **kwargs)
return wrapper
return decorator
