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# -*- coding: utf-8 -*-
#
# Copyright 2009-2017 Wander Lairson Costa
# Copyright 2009-2021 PyUSB contributors
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#
# 2. Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in the
# documentation and/or other materials provided with the distribution.
#
# 3. Neither the name of the copyright holder nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
import sys
__all__ = ['AutoFinalizedObject']
class _AutoFinalizedObjectBase(object):
"""
Base class for objects that get automatically
finalized on delete or at exit.
"""
def _finalize_object(self):
"""Actually finalizes the object (frees allocated resources etc.).
Returns: None
Derived classes should implement this.
"""
pass
def __new__(cls, *args, **kwargs):
"""Creates a new object instance and adds the private finalizer
attributes to it.
Returns: new object instance
Arguments:
* *args, **kwargs -- ignored
"""
instance = super(_AutoFinalizedObjectBase, cls).__new__(cls)
instance._finalize_called = False
return instance
def _do_finalize_object(self):
"""Helper method that finalizes the object if not already done.
Returns: None
"""
if not self._finalize_called: # race-free?
self._finalize_called = True
self._finalize_object()
def finalize(self):
"""Finalizes the object if not already done.
Returns: None
"""
# this is the "public" finalize method
raise NotImplementedError(
"finalize() must be implemented by AutoFinalizedObject."
)
def __del__(self):
self.finalize()
if sys.hexversion >= 0x3040000:
# python >= 3.4: use weakref.finalize
import weakref
def _do_finalize_object_ref(obj_ref):
"""Helper function for weakref.finalize() that dereferences a weakref
to an object and calls its _do_finalize_object() method if the object
is still alive. Does nothing otherwise.
Returns: None (implicit)
Arguments:
* obj_ref -- weakref to an object
"""
obj = obj_ref()
if obj is not None:
# else object disappeared
obj._do_finalize_object()
class AutoFinalizedObject(_AutoFinalizedObjectBase):
def __new__(cls, *args, **kwargs):
"""Creates a new object instance and adds the private finalizer
attributes to it.
Returns: new object instance
Arguments:
* *args, **kwargs -- passed to the parent instance creator
(which ignores them)
"""
# Note: Do not pass a (hard) reference to instance to the
# finalizer as func/args/kwargs, it'd keep the object
# alive until the program terminates.
# A weak reference is fine.
#
# Note 2: When using weakrefs and not calling finalize() in
# __del__, the object may already have disappeared
# when weakref.finalize() kicks in.
# Make sure that _finalizer() gets called,
# i.e. keep __del__() from the base class.
#
# Note 3: the _finalize_called attribute is (probably) useless
# for this class
instance = super(AutoFinalizedObject, cls).__new__(
cls, *args, **kwargs
)
instance._finalizer = weakref.finalize(
instance, _do_finalize_object_ref, weakref.ref(instance)
)
return instance
def finalize(self):
"""Finalizes the object if not already done."""
self._finalizer()
else:
# python < 3.4: keep the old behavior (rely on __del__),
# but don't call _finalize_object() more than once
class AutoFinalizedObject(_AutoFinalizedObjectBase):
def finalize(self):
"""Finalizes the object if not already done."""
self._do_finalize_object()
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