81 lines
2.9 KiB
Python
81 lines
2.9 KiB
Python
# Copyright 2016 Google Inc. All rights reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import errno
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import fcntl
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import time
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from oauth2client.contrib import locked_file
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class _FcntlOpener(locked_file._Opener):
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"""Open, lock, and unlock a file using fcntl.lockf."""
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def open_and_lock(self, timeout, delay):
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"""Open the file and lock it.
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Args:
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timeout: float, How long to try to lock for.
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delay: float, How long to wait between retries
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Raises:
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AlreadyLockedException: if the lock is already acquired.
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IOError: if the open fails.
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CredentialsFileSymbolicLinkError: if the file is a symbolic
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link.
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"""
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if self._locked:
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raise locked_file.AlreadyLockedException(
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'File {0} is already locked'.format(self._filename))
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start_time = time.time()
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locked_file.validate_file(self._filename)
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try:
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self._fh = open(self._filename, self._mode)
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except IOError as e:
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# If we can't access with _mode, try _fallback_mode and
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# don't lock.
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if e.errno in (errno.EPERM, errno.EACCES):
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self._fh = open(self._filename, self._fallback_mode)
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return
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# We opened in _mode, try to lock the file.
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while True:
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try:
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fcntl.lockf(self._fh.fileno(), fcntl.LOCK_EX)
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self._locked = True
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return
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except IOError as e:
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# If not retrying, then just pass on the error.
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if timeout == 0:
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raise
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if e.errno != errno.EACCES:
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raise
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# We could not acquire the lock. Try again.
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if (time.time() - start_time) >= timeout:
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locked_file.logger.warn('Could not lock %s in %s seconds',
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self._filename, timeout)
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if self._fh:
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self._fh.close()
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self._fh = open(self._filename, self._fallback_mode)
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return
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time.sleep(delay)
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def unlock_and_close(self):
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"""Close and unlock the file using the fcntl.lockf primitive."""
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if self._locked:
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fcntl.lockf(self._fh.fileno(), fcntl.LOCK_UN)
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self._locked = False
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if self._fh:
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self._fh.close()
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