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