View file File name : process_lock.py Content :# -*- 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. """ 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 = 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): self.acquire() 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): raise NotImplementedError() def unlock(self): raise NotImplementedError() class _WindowsLock(_InterProcessLock): """Interprocess lock implementation that works on windows systems.""" def trylock(self): msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_NBLCK, 1) def unlock(self): msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_UNLCK, 1) class _FcntlLock(_InterProcessLock): """Interprocess lock implementation that works on posix systems.""" 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 = _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