forked from mirrors/gecko-dev
c8b4aaeb2d
Backed out changeset 09f7f3d1c6dd (bug 1766497) Backed out changeset 6bb5f754957a (bug 1766497) Backed out changeset aedf2d7af408 (bug 1766497) Backed out changeset 394555265c86 (bug 1766497) Backed out changeset 41be40696e00 (bug 1766497)
451 lines
13 KiB
Python
451 lines
13 KiB
Python
# This is free and unencumbered software released into the public domain.
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#
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# Anyone is free to copy, modify, publish, use, compile, sell, or
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# distribute this software, either in source code form or as a compiled
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# binary, for any purpose, commercial or non-commercial, and by any
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# means.
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#
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# In jurisdictions that recognize copyright laws, the author or authors
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# of this software dedicate any and all copyright interest in the
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# software to the public domain. We make this dedication for the benefit
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# of the public at large and to the detriment of our heirs and
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# successors. We intend this dedication to be an overt act of
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# relinquishment in perpetuity of all present and future rights to this
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# software under copyright law.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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# IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
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# OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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# ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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# OTHER DEALINGS IN THE SOFTWARE.
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#
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# For more information, please refer to <http://unlicense.org>
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"""
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A platform independent file lock that supports the with-statement.
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"""
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# Modules
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# ------------------------------------------------
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import logging
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import os
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import threading
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import time
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try:
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import warnings
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except ImportError:
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warnings = None
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try:
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import msvcrt
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except ImportError:
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msvcrt = None
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try:
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import fcntl
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except ImportError:
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fcntl = None
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# Backward compatibility
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# ------------------------------------------------
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try:
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TimeoutError
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except NameError:
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TimeoutError = OSError
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# Data
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# ------------------------------------------------
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__all__ = [
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"Timeout",
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"BaseFileLock",
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"WindowsFileLock",
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"UnixFileLock",
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"SoftFileLock",
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"FileLock"
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]
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__version__ = "3.0.12"
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_logger = None
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def logger():
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"""Returns the logger instance used in this module."""
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global _logger
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_logger = _logger or logging.getLogger(__name__)
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return _logger
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# Exceptions
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# ------------------------------------------------
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class Timeout(TimeoutError):
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"""
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Raised when the lock could not be acquired in *timeout*
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seconds.
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"""
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def __init__(self, lock_file):
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"""
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"""
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#: The path of the file lock.
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self.lock_file = lock_file
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return None
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def __str__(self):
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temp = "The file lock '{}' could not be acquired."\
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.format(self.lock_file)
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return temp
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# Classes
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# ------------------------------------------------
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# This is a helper class which is returned by :meth:`BaseFileLock.acquire`
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# and wraps the lock to make sure __enter__ is not called twice when entering
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# the with statement.
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# If we would simply return *self*, the lock would be acquired again
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# in the *__enter__* method of the BaseFileLock, but not released again
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# automatically.
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#
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# :seealso: issue #37 (memory leak)
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class _Acquire_ReturnProxy(object):
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def __init__(self, lock):
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self.lock = lock
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return None
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def __enter__(self):
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return self.lock
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def __exit__(self, exc_type, exc_value, traceback):
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self.lock.release()
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return None
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class BaseFileLock(object):
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"""
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Implements the base class of a file lock.
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"""
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def __init__(self, lock_file, timeout = -1):
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"""
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"""
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# The path to the lock file.
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self._lock_file = lock_file
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# The file descriptor for the *_lock_file* as it is returned by the
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# os.open() function.
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# This file lock is only NOT None, if the object currently holds the
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# lock.
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self._lock_file_fd = None
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# The default timeout value.
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self.timeout = timeout
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# We use this lock primarily for the lock counter.
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self._thread_lock = threading.Lock()
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# The lock counter is used for implementing the nested locking
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# mechanism. Whenever the lock is acquired, the counter is increased and
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# the lock is only released, when this value is 0 again.
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self._lock_counter = 0
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return None
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@property
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def lock_file(self):
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"""
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The path to the lock file.
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"""
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return self._lock_file
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@property
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def timeout(self):
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"""
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You can set a default timeout for the filelock. It will be used as
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fallback value in the acquire method, if no timeout value (*None*) is
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given.
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If you want to disable the timeout, set it to a negative value.
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A timeout of 0 means, that there is exactly one attempt to acquire the
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file lock.
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.. versionadded:: 2.0.0
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"""
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return self._timeout
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@timeout.setter
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def timeout(self, value):
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"""
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"""
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self._timeout = float(value)
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return None
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# Platform dependent locking
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# --------------------------------------------
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def _acquire(self):
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"""
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Platform dependent. If the file lock could be
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acquired, self._lock_file_fd holds the file descriptor
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of the lock file.
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"""
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raise NotImplementedError()
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def _release(self):
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"""
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Releases the lock and sets self._lock_file_fd to None.
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"""
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raise NotImplementedError()
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# Platform independent methods
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# --------------------------------------------
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@property
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def is_locked(self):
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"""
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True, if the object holds the file lock.
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.. versionchanged:: 2.0.0
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This was previously a method and is now a property.
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"""
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return self._lock_file_fd is not None
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def acquire(self, timeout=None, poll_intervall=0.05):
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"""
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Acquires the file lock or fails with a :exc:`Timeout` error.
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.. code-block:: python
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# You can use this method in the context manager (recommended)
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with lock.acquire():
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pass
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# Or use an equivalent try-finally construct:
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lock.acquire()
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try:
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pass
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finally:
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lock.release()
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:arg float timeout:
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The maximum time waited for the file lock.
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If ``timeout < 0``, there is no timeout and this method will
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block until the lock could be acquired.
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If ``timeout`` is None, the default :attr:`~timeout` is used.
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:arg float poll_intervall:
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We check once in *poll_intervall* seconds if we can acquire the
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file lock.
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:raises Timeout:
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if the lock could not be acquired in *timeout* seconds.
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.. versionchanged:: 2.0.0
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This method returns now a *proxy* object instead of *self*,
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so that it can be used in a with statement without side effects.
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"""
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# Use the default timeout, if no timeout is provided.
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if timeout is None:
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timeout = self.timeout
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# Increment the number right at the beginning.
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# We can still undo it, if something fails.
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with self._thread_lock:
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self._lock_counter += 1
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lock_id = id(self)
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lock_filename = self._lock_file
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start_time = time.time()
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try:
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while True:
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with self._thread_lock:
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if not self.is_locked:
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logger().debug('Attempting to acquire lock %s on %s', lock_id, lock_filename)
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self._acquire()
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if self.is_locked:
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logger().info('Lock %s acquired on %s', lock_id, lock_filename)
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break
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elif timeout >= 0 and time.time() - start_time > timeout:
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logger().debug('Timeout on acquiring lock %s on %s', lock_id, lock_filename)
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raise Timeout(self._lock_file)
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else:
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logger().debug(
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'Lock %s not acquired on %s, waiting %s seconds ...',
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lock_id, lock_filename, poll_intervall
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)
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time.sleep(poll_intervall)
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except:
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# Something did go wrong, so decrement the counter.
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with self._thread_lock:
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self._lock_counter = max(0, self._lock_counter - 1)
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raise
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return _Acquire_ReturnProxy(lock = self)
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def release(self, force = False):
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"""
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Releases the file lock.
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Please note, that the lock is only completly released, if the lock
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counter is 0.
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Also note, that the lock file itself is not automatically deleted.
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:arg bool force:
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If true, the lock counter is ignored and the lock is released in
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every case.
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"""
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with self._thread_lock:
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if self.is_locked:
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self._lock_counter -= 1
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if self._lock_counter == 0 or force:
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lock_id = id(self)
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lock_filename = self._lock_file
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logger().debug('Attempting to release lock %s on %s', lock_id, lock_filename)
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self._release()
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self._lock_counter = 0
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logger().info('Lock %s released on %s', lock_id, lock_filename)
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return None
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def __enter__(self):
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self.acquire()
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return self
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def __exit__(self, exc_type, exc_value, traceback):
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self.release()
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return None
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def __del__(self):
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self.release(force = True)
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return None
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# Windows locking mechanism
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# ~~~~~~~~~~~~~~~~~~~~~~~~~
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class WindowsFileLock(BaseFileLock):
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"""
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Uses the :func:`msvcrt.locking` function to hard lock the lock file on
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windows systems.
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"""
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def _acquire(self):
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open_mode = os.O_RDWR | os.O_CREAT | os.O_TRUNC
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try:
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fd = os.open(self._lock_file, open_mode)
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except OSError:
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pass
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else:
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try:
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msvcrt.locking(fd, msvcrt.LK_NBLCK, 1)
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except (IOError, OSError):
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os.close(fd)
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else:
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self._lock_file_fd = fd
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return None
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def _release(self):
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fd = self._lock_file_fd
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self._lock_file_fd = None
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msvcrt.locking(fd, msvcrt.LK_UNLCK, 1)
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os.close(fd)
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try:
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os.remove(self._lock_file)
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# Probably another instance of the application
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# that acquired the file lock.
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except OSError:
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pass
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return None
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# Unix locking mechanism
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# ~~~~~~~~~~~~~~~~~~~~~~
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class UnixFileLock(BaseFileLock):
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"""
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Uses the :func:`fcntl.flock` to hard lock the lock file on unix systems.
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"""
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def _acquire(self):
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open_mode = os.O_RDWR | os.O_CREAT | os.O_TRUNC
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fd = os.open(self._lock_file, open_mode)
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try:
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fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
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except (IOError, OSError):
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os.close(fd)
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else:
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self._lock_file_fd = fd
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return None
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def _release(self):
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# Do not remove the lockfile:
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#
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# https://github.com/benediktschmitt/py-filelock/issues/31
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# https://stackoverflow.com/questions/17708885/flock-removing-locked-file-without-race-condition
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fd = self._lock_file_fd
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self._lock_file_fd = None
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fcntl.flock(fd, fcntl.LOCK_UN)
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os.close(fd)
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return None
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# Soft lock
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# ~~~~~~~~~
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class SoftFileLock(BaseFileLock):
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"""
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Simply watches the existence of the lock file.
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"""
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def _acquire(self):
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open_mode = os.O_WRONLY | os.O_CREAT | os.O_EXCL | os.O_TRUNC
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try:
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fd = os.open(self._lock_file, open_mode)
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except (IOError, OSError):
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pass
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else:
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self._lock_file_fd = fd
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return None
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def _release(self):
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os.close(self._lock_file_fd)
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self._lock_file_fd = None
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try:
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os.remove(self._lock_file)
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# The file is already deleted and that's what we want.
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except OSError:
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pass
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return None
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# Platform filelock
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# ~~~~~~~~~~~~~~~~~
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#: Alias for the lock, which should be used for the current platform. On
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#: Windows, this is an alias for :class:`WindowsFileLock`, on Unix for
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#: :class:`UnixFileLock` and otherwise for :class:`SoftFileLock`.
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FileLock = None
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if msvcrt:
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FileLock = WindowsFileLock
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elif fcntl:
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FileLock = UnixFileLock
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else:
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FileLock = SoftFileLock
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if warnings is not None:
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warnings.warn("only soft file lock is available")
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