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# Copyright 2016 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.
import errno
import fcntl
import time
from oauth2client.contrib import locked_file
class _FcntlOpener(locked_file._Opener):
"""Open, lock, and unlock a file using fcntl.lockf."""
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
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 locked_file.AlreadyLockedException(
'File {0} is already locked'.format(self._filename))
start_time = time.time()
locked_file.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 in (errno.EPERM, errno.EACCES):
self._fh = open(self._filename, self._fallback_mode)
return
# We opened in _mode, try to lock the file.
while True:
try:
fcntl.lockf(self._fh.fileno(), fcntl.LOCK_EX)
self._locked = True
return
except IOError as e:
# If not retrying, then just pass on the error.
if timeout == 0:
raise
if e.errno != errno.EACCES:
raise
# We could not acquire the lock. Try again.
if (time.time() - start_time) >= timeout:
locked_file.logger.warn('Could not lock %s in %s seconds',
self._filename, timeout)
if self._fh:
self._fh.close()
self._fh = open(self._filename, self._fallback_mode)
return
time.sleep(delay)
def unlock_and_close(self):
"""Close and unlock the file using the fcntl.lockf primitive."""
if self._locked:
fcntl.lockf(self._fh.fileno(), fcntl.LOCK_UN)
self._locked = False
if self._fh:
self._fh.close()
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