Edit file

File name : _objfinalizer.py

Content :# -*- coding: utf-8 -*- # # Copyright (C) 2014 André Erdmann # # The following terms apply to all files associated # with the software unless explicitly disclaimed in individual files. # # The authors hereby grant permission to use, copy, modify, distribute, # and license this software and its documentation for any purpose, provided # that existing copyright notices are retained in all copies and that this # notice is included verbatim in any distributions. No written agreement, # license, or royalty fee is required for any of the authorized uses. # Modifications to this software may be copyrighted by their authors # and need not follow the licensing terms described here, provided that # the new terms are clearly indicated on the first page of each file where # they apply. # # IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY # FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES # ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY # DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE # POSSIBILITY OF SUCH DAMAGE. # # THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES, # INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, # FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT. THIS SOFTWARE # IS PROVIDED ON AN "AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE # NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR # MODIFICATIONS. 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()

Save