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import logging
import time
from threading import Lock
from ._error import Timeout
_LOGGER = logging.getLogger("filelock")
_LOGGER.setLevel(logging.DEBUG)
# This is a helper class which is returned by :meth:`BaseFileLock.acquire` and wraps the lock to make sure __enter__
# is not called twice when entering the with statement. If we would simply return *self*, the lock would be acquired
# again in the *__enter__* method of the BaseFileLock, but not released again automatically. issue #37 (memory leak)
class AcquireReturnProxy(object):
"""A context aware object that will release the lock file when exiting."""
def __init__(self, lock):
self.lock = lock
def __enter__(self):
return self.lock
def __exit__(self, exc_type, exc_value, traceback): # noqa: U100
self.lock.release()
class BaseFileLock(object):
"""Abstract base class for a file lock object."""
def __init__(self, lock_file, timeout=-1):
"""
Create a new lock object.
:param lock_file: path to the file
:param timeout: default timeout when acquiring the lock. It will be used as fallback value in the acquire
method, if no timeout value (``None``) is given. If you want to disable the timeout, set it to a negative value.
A timeout of 0 means, that there is exactly one attempt to acquire the file lock.
"""
# The path to the lock file.
self._lock_file = lock_file
# The file descriptor for the *_lock_file* as it is returned by the os.open() function.
# This file lock is only NOT None, if the object currently holds the lock.
self._lock_file_fd = None
# The default timeout value.
self.timeout = timeout
# We use this lock primarily for the lock counter.
self._thread_lock = Lock()
# The lock counter is used for implementing the nested locking mechanism. Whenever the lock is acquired, the
# counter is increased and the lock is only released, when this value is 0 again.
self._lock_counter = 0
@property
def lock_file(self):
""":return: path to the lock file"""
return self._lock_file
@property
def timeout(self):
"""
:return: the default timeout value
.. versionadded:: 2.0.0
"""
return self._timeout
@timeout.setter
def timeout(self, value):
"""
Change the default timeout value.
:param value: the new value
"""
self._timeout = float(value)
def _acquire(self):
"""If the file lock could be acquired, self._lock_file_fd holds the file descriptor of the lock file."""
raise NotImplementedError
def _release(self):
"""Releases the lock and sets self._lock_file_fd to None."""
raise NotImplementedError
@property
def is_locked(self):
"""
:return: A boolean indicating if the lock file is holding the lock currently.
.. versionchanged:: 2.0.0
This was previously a method and is now a property.
"""
return self._lock_file_fd is not None
def acquire(self, timeout=None, poll_intervall=0.05):
"""
Try to acquire the file lock.
:param timeout: maximum wait time for acquiring the lock, ``None`` means use the default :attr:`~timeout` is and
if ``timeout < 0``, there is no timeout and this method will block until the lock could be acquired
:param poll_intervall: interval of trying to acquire the lock file
:raises Timeout: if fails to acquire lock within the timeout period
:return: a context object that will unlock the file when the context is exited
.. code-block:: python
# You can use this method in the context manager (recommended)
with lock.acquire():
pass
# Or use an equivalent try-finally construct:
lock.acquire()
try:
pass
finally:
lock.release()
.. versionchanged:: 2.0.0
This method returns now a *proxy* object instead of *self*,
so that it can be used in a with statement without side effects.
"""
# Use the default timeout, if no timeout is provided.
if timeout is None:
timeout = self.timeout
# Increment the number right at the beginning. We can still undo it, if something fails.
with self._thread_lock:
self._lock_counter += 1
lock_id = id(self)
lock_filename = self._lock_file
start_time = time.time()
try:
while True:
with self._thread_lock:
if not self.is_locked:
_LOGGER.debug("Attempting to acquire lock %s on %s", lock_id, lock_filename)
self._acquire()
if self.is_locked:
_LOGGER.debug("Lock %s acquired on %s", lock_id, lock_filename)
break
elif 0 <= timeout < time.time() - start_time:
_LOGGER.debug("Timeout on acquiring lock %s on %s", lock_id, lock_filename)
raise Timeout(self._lock_file)
else:
msg = "Lock %s not acquired on %s, waiting %s seconds ..."
_LOGGER.debug(msg, lock_id, lock_filename, poll_intervall)
time.sleep(poll_intervall)
except BaseException: # Something did go wrong, so decrement the counter.
with self._thread_lock:
self._lock_counter = max(0, self._lock_counter - 1)
raise
return AcquireReturnProxy(lock=self)
def release(self, force=False):
"""
Releases the file lock. Please note, that the lock is only completely released, if the lock counter is 0. Also
note, that the lock file itself is not automatically deleted.
:param force: If true, the lock counter is ignored and the lock is released in every case/
"""
with self._thread_lock:
if self.is_locked:
self._lock_counter -= 1
if self._lock_counter == 0 or force:
lock_id, lock_filename = id(self), self._lock_file
_LOGGER.debug("Attempting to release lock %s on %s", lock_id, lock_filename)
self._release()
self._lock_counter = 0
_LOGGER.debug("Lock %s released on %s", lock_id, lock_filename)
def __enter__(self):
"""
Acquire the lock.
:return: the lock object
"""
self.acquire()
return self
def __exit__(self, exc_type, exc_value, traceback): # noqa: U100
"""
Release the lock.
:param exc_type: the exception type if raised
:param exc_value: the exception value if raised
:param traceback: the exception traceback if raised
"""
self.release()
def __del__(self):
"""Called when the lock object is deleted."""
self.release(force=True)
__all__ = [
"BaseFileLock",
"AcquireReturnProxy",
]
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