234 lines
7.4 KiB
Python
234 lines
7.4 KiB
Python
# Copyright 2014 Google Inc. 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.
|
|
|
|
"""Locked file interface that should work on Unix and Windows pythons.
|
|
|
|
This module first tries to use fcntl locking to ensure serialized access
|
|
to a file, then falls back on a lock file if that is unavialable.
|
|
|
|
Usage::
|
|
|
|
f = LockedFile('filename', 'r+b', 'rb')
|
|
f.open_and_lock()
|
|
if f.is_locked():
|
|
print('Acquired filename with r+b mode')
|
|
f.file_handle().write('locked data')
|
|
else:
|
|
print('Acquired filename with rb mode')
|
|
f.unlock_and_close()
|
|
|
|
"""
|
|
|
|
from __future__ import print_function
|
|
|
|
import errno
|
|
import logging
|
|
import os
|
|
import time
|
|
|
|
from oauth2client import util
|
|
|
|
|
|
__author__ = 'cache@google.com (David T McWherter)'
|
|
|
|
logger = logging.getLogger(__name__)
|
|
|
|
|
|
class CredentialsFileSymbolicLinkError(Exception):
|
|
"""Credentials files must not be symbolic links."""
|
|
|
|
|
|
class AlreadyLockedException(Exception):
|
|
"""Trying to lock a file that has already been locked by the LockedFile."""
|
|
pass
|
|
|
|
|
|
def validate_file(filename):
|
|
if os.path.islink(filename):
|
|
raise CredentialsFileSymbolicLinkError(
|
|
'File: {0} is a symbolic link.'.format(filename))
|
|
|
|
|
|
class _Opener(object):
|
|
"""Base class for different locking primitives."""
|
|
|
|
def __init__(self, filename, mode, fallback_mode):
|
|
"""Create an Opener.
|
|
|
|
Args:
|
|
filename: string, The pathname of the file.
|
|
mode: string, The preferred mode to access the file with.
|
|
fallback_mode: string, The mode to use if locking fails.
|
|
"""
|
|
self._locked = False
|
|
self._filename = filename
|
|
self._mode = mode
|
|
self._fallback_mode = fallback_mode
|
|
self._fh = None
|
|
self._lock_fd = None
|
|
|
|
def is_locked(self):
|
|
"""Was the file locked."""
|
|
return self._locked
|
|
|
|
def file_handle(self):
|
|
"""The file handle to the file. Valid only after opened."""
|
|
return self._fh
|
|
|
|
def filename(self):
|
|
"""The filename that is being locked."""
|
|
return self._filename
|
|
|
|
def open_and_lock(self, timeout, delay):
|
|
"""Open the file and lock it.
|
|
|
|
Args:
|
|
timeout: float, How long to try to lock for.
|
|
delay: float, How long to wait between retries.
|
|
"""
|
|
pass
|
|
|
|
def unlock_and_close(self):
|
|
"""Unlock and close the file."""
|
|
pass
|
|
|
|
|
|
class _PosixOpener(_Opener):
|
|
"""Lock files using Posix advisory lock files."""
|
|
|
|
def open_and_lock(self, timeout, delay):
|
|
"""Open the file and lock it.
|
|
|
|
Tries to create a .lock file next to the file we're trying to open.
|
|
|
|
Args:
|
|
timeout: float, How long to try to lock for.
|
|
delay: float, How long to wait between retries.
|
|
|
|
Raises:
|
|
AlreadyLockedException: if the lock is already acquired.
|
|
IOError: if the open fails.
|
|
CredentialsFileSymbolicLinkError if the file is a symbolic link.
|
|
"""
|
|
if self._locked:
|
|
raise AlreadyLockedException(
|
|
'File {0} is already locked'.format(self._filename))
|
|
self._locked = False
|
|
|
|
validate_file(self._filename)
|
|
try:
|
|
self._fh = open(self._filename, self._mode)
|
|
except IOError as e:
|
|
# If we can't access with _mode, try _fallback_mode and don't lock.
|
|
if e.errno == errno.EACCES:
|
|
self._fh = open(self._filename, self._fallback_mode)
|
|
return
|
|
|
|
lock_filename = self._posix_lockfile(self._filename)
|
|
start_time = time.time()
|
|
while True:
|
|
try:
|
|
self._lock_fd = os.open(lock_filename,
|
|
os.O_CREAT | os.O_EXCL | os.O_RDWR)
|
|
self._locked = True
|
|
break
|
|
|
|
except OSError as e:
|
|
if e.errno != errno.EEXIST:
|
|
raise
|
|
if (time.time() - start_time) >= timeout:
|
|
logger.warn('Could not acquire lock %s in %s seconds',
|
|
lock_filename, timeout)
|
|
# Close the file and open in fallback_mode.
|
|
if self._fh:
|
|
self._fh.close()
|
|
self._fh = open(self._filename, self._fallback_mode)
|
|
return
|
|
time.sleep(delay)
|
|
|
|
def unlock_and_close(self):
|
|
"""Unlock a file by removing the .lock file, and close the handle."""
|
|
if self._locked:
|
|
lock_filename = self._posix_lockfile(self._filename)
|
|
os.close(self._lock_fd)
|
|
os.unlink(lock_filename)
|
|
self._locked = False
|
|
self._lock_fd = None
|
|
if self._fh:
|
|
self._fh.close()
|
|
|
|
def _posix_lockfile(self, filename):
|
|
"""The name of the lock file to use for posix locking."""
|
|
return '{0}.lock'.format(filename)
|
|
|
|
|
|
class LockedFile(object):
|
|
"""Represent a file that has exclusive access."""
|
|
|
|
@util.positional(4)
|
|
def __init__(self, filename, mode, fallback_mode, use_native_locking=True):
|
|
"""Construct a LockedFile.
|
|
|
|
Args:
|
|
filename: string, The path of the file to open.
|
|
mode: string, The mode to try to open the file with.
|
|
fallback_mode: string, The mode to use if locking fails.
|
|
use_native_locking: bool, Whether or not fcntl/win32 locking is
|
|
used.
|
|
"""
|
|
opener = None
|
|
if not opener and use_native_locking:
|
|
try:
|
|
from oauth2client.contrib._win32_opener import _Win32Opener
|
|
opener = _Win32Opener(filename, mode, fallback_mode)
|
|
except ImportError:
|
|
try:
|
|
from oauth2client.contrib._fcntl_opener import _FcntlOpener
|
|
opener = _FcntlOpener(filename, mode, fallback_mode)
|
|
except ImportError:
|
|
pass
|
|
|
|
if not opener:
|
|
opener = _PosixOpener(filename, mode, fallback_mode)
|
|
|
|
self._opener = opener
|
|
|
|
def filename(self):
|
|
"""Return the filename we were constructed with."""
|
|
return self._opener._filename
|
|
|
|
def file_handle(self):
|
|
"""Return the file_handle to the opened file."""
|
|
return self._opener.file_handle()
|
|
|
|
def is_locked(self):
|
|
"""Return whether we successfully locked the file."""
|
|
return self._opener.is_locked()
|
|
|
|
def open_and_lock(self, timeout=0, delay=0.05):
|
|
"""Open the file, trying to lock it.
|
|
|
|
Args:
|
|
timeout: float, The number of seconds to try to acquire the lock.
|
|
delay: float, The number of seconds to wait between retry attempts.
|
|
|
|
Raises:
|
|
AlreadyLockedException: if the lock is already acquired.
|
|
IOError: if the open fails.
|
|
"""
|
|
self._opener.open_and_lock(timeout, delay)
|
|
|
|
def unlock_and_close(self):
|
|
"""Unlock and close a file."""
|
|
self._opener.unlock_and_close()
|