247 lines
8.7 KiB
Python
247 lines
8.7 KiB
Python
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from __future__ import annotations
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import contextlib
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import logging
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import os
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import time
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import warnings
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from abc import ABC, abstractmethod
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from threading import Lock
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from types import TracebackType
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from typing import Any
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from ._error import Timeout
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_LOGGER = logging.getLogger("filelock")
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# This is a helper class which is returned by :meth:`BaseFileLock.acquire` and wraps the lock to make sure __enter__
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# is not called twice when entering the with statement. If we would simply return *self*, the lock would be acquired
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# again in the *__enter__* method of the BaseFileLock, but not released again automatically. issue #37 (memory leak)
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class AcquireReturnProxy:
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"""A context aware object that will release the lock file when exiting."""
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def __init__(self, lock: BaseFileLock) -> None:
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self.lock = lock
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def __enter__(self) -> BaseFileLock:
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return self.lock
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def __exit__(
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self,
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exc_type: type[BaseException] | None, # noqa: U100
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exc_value: BaseException | None, # noqa: U100
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traceback: TracebackType | None, # noqa: U100
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) -> None:
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self.lock.release()
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class BaseFileLock(ABC, contextlib.ContextDecorator):
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"""Abstract base class for a file lock object."""
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def __init__(self, lock_file: str | os.PathLike[Any], timeout: float = -1) -> None:
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"""
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Create a new lock object.
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:param lock_file: path to the file
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:param timeout: default timeout when acquiring the lock, in seconds. It will be used as fallback value in
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the acquire method, if no timeout value (``None``) is given. If you want to disable the timeout, set it
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to a negative value. A timeout of 0 means, that there is exactly one attempt to acquire the file lock.
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"""
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# The path to the lock file.
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self._lock_file: str = os.fspath(lock_file)
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# The file descriptor for the *_lock_file* as it is returned by the os.open() function.
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# This file lock is only NOT None, if the object currently holds the lock.
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self._lock_file_fd: int | None = None
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# The default timeout value.
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self.timeout: float = timeout
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# We use this lock primarily for the lock counter.
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self._thread_lock: Lock = Lock()
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# The lock counter is used for implementing the nested locking mechanism. Whenever the lock is acquired, the
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# counter is increased and the lock is only released, when this value is 0 again.
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self._lock_counter: int = 0
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@property
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def lock_file(self) -> str:
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""":return: path to the lock file"""
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return self._lock_file
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@property
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def timeout(self) -> float:
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"""
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:return: the default timeout value, in seconds
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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: float | str) -> None:
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"""
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Change the default timeout value.
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:param value: the new value, in seconds
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"""
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self._timeout = float(value)
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@abstractmethod
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def _acquire(self) -> None:
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"""If the file lock could be acquired, self._lock_file_fd holds the file descriptor of the lock file."""
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raise NotImplementedError
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@abstractmethod
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def _release(self) -> None:
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"""Releases the lock and sets self._lock_file_fd to None."""
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raise NotImplementedError
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@property
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def is_locked(self) -> bool:
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"""
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:return: A boolean indicating if the lock file is holding the lock currently.
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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(
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self,
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timeout: float | None = None,
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poll_interval: float = 0.05,
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*,
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poll_intervall: float | None = None,
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blocking: bool = True,
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) -> AcquireReturnProxy:
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"""
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Try to acquire the file lock.
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:param timeout: maximum wait time for acquiring the lock, ``None`` means use the default :attr:`~timeout` is and
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if ``timeout < 0``, there is no timeout and this method will block until the lock could be acquired
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:param poll_interval: interval of trying to acquire the lock file
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:param poll_intervall: deprecated, kept for backwards compatibility, use ``poll_interval`` instead
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:param blocking: defaults to True. If False, function will return immediately if it cannot obtain a lock on the
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first attempt. Otherwise this method will block until the timeout expires or the lock is acquired.
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:raises Timeout: if fails to acquire lock within the timeout period
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:return: a context object that will unlock the file when the context is exited
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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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.. 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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if poll_intervall is not None:
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msg = "use poll_interval instead of poll_intervall"
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warnings.warn(msg, DeprecationWarning, stacklevel=2)
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poll_interval = poll_intervall
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# Increment the number right at the beginning. 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.monotonic()
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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.debug("Lock %s acquired on %s", lock_id, lock_filename)
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break
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elif blocking is False:
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_LOGGER.debug("Failed to immediately acquire lock %s on %s", lock_id, lock_filename)
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raise Timeout(self._lock_file)
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elif 0 <= timeout < time.monotonic() - start_time:
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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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msg = "Lock %s not acquired on %s, waiting %s seconds ..."
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_LOGGER.debug(msg, lock_id, lock_filename, poll_interval)
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time.sleep(poll_interval)
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except BaseException: # 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 AcquireReturnProxy(lock=self)
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def release(self, force: bool = False) -> None:
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"""
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Releases the file lock. Please note, that the lock is only completely released, if the lock counter is 0. Also
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note, that the lock file itself is not automatically deleted.
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:param force: If true, the lock counter is ignored and the lock is released in 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, lock_filename = id(self), 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.debug("Lock %s released on %s", lock_id, lock_filename)
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def __enter__(self) -> BaseFileLock:
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"""
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Acquire the lock.
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:return: the lock object
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"""
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self.acquire()
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return self
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def __exit__(
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self,
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exc_type: type[BaseException] | None, # noqa: U100
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exc_value: BaseException | None, # noqa: U100
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traceback: TracebackType | None, # noqa: U100
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) -> None:
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"""
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Release the lock.
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:param exc_type: the exception type if raised
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:param exc_value: the exception value if raised
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:param traceback: the exception traceback if raised
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"""
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self.release()
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def __del__(self) -> None:
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"""Called when the lock object is deleted."""
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self.release(force=True)
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__all__ = [
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"BaseFileLock",
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"AcquireReturnProxy",
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]
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