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172 lines
7.2 KiB
172 lines
7.2 KiB
"""Refactored "safe reference" from dispatcher.py"""
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import weakref, traceback, sys
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if sys.hexversion >= 0x3000000:
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im_func = '__func__'
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im_self = '__self__'
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else:
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im_func = 'im_func'
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im_self = 'im_self'
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def safeRef(target, onDelete = None):
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"""Return a *safe* weak reference to a callable target
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target -- the object to be weakly referenced, if it's a
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bound method reference, will create a BoundMethodWeakref,
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otherwise creates a simple weakref.
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onDelete -- if provided, will have a hard reference stored
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to the callable to be called after the safe reference
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goes out of scope with the reference object, (either a
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weakref or a BoundMethodWeakref) as argument.
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"""
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if hasattr(target, im_self):
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if getattr(target, im_self) is not None:
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# Turn a bound method into a BoundMethodWeakref instance.
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# Keep track of these instances for lookup by disconnect().
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assert hasattr(target, im_func), """safeRef target %r has %s, but no %s, don't know how to create reference"""%( target,im_self,im_func)
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reference = BoundMethodWeakref(
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target=target,
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onDelete=onDelete
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)
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return reference
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if onDelete is not None:
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return weakref.ref(target, onDelete)
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else:
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return weakref.ref( target )
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class BoundMethodWeakref(object):
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"""'Safe' and reusable weak references to instance methods
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BoundMethodWeakref objects provide a mechanism for
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referencing a bound method without requiring that the
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method object itself (which is normally a transient
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object) is kept alive. Instead, the BoundMethodWeakref
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object keeps weak references to both the object and the
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function which together define the instance method.
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Attributes:
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key -- the identity key for the reference, calculated
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by the class's calculateKey method applied to the
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target instance method
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deletionMethods -- sequence of callable objects taking
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single argument, a reference to this object which
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will be called when *either* the target object or
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target function is garbage collected (i.e. when
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this object becomes invalid). These are specified
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as the onDelete parameters of safeRef calls.
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weakSelf -- weak reference to the target object
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weakFunc -- weak reference to the target function
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Class Attributes:
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_allInstances -- class attribute pointing to all live
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BoundMethodWeakref objects indexed by the class's
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calculateKey(target) method applied to the target
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objects. This weak value dictionary is used to
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short-circuit creation so that multiple references
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to the same (object, function) pair produce the
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same BoundMethodWeakref instance.
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"""
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_allInstances = weakref.WeakValueDictionary()
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def __new__( cls, target, onDelete=None, *arguments,**named ):
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"""Create new instance or return current instance
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Basically this method of construction allows us to
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short-circuit creation of references to already-
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referenced instance methods. The key corresponding
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to the target is calculated, and if there is already
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an existing reference, that is returned, with its
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deletionMethods attribute updated. Otherwise the
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new instance is created and registered in the table
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of already-referenced methods.
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"""
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key = cls.calculateKey(target)
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current =cls._allInstances.get(key)
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if current is not None:
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current.deletionMethods.append( onDelete)
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return current
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else:
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base = super( BoundMethodWeakref, cls).__new__( cls )
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cls._allInstances[key] = base
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base.__init__( target, onDelete, *arguments,**named)
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return base
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def __init__(self, target, onDelete=None):
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"""Return a weak-reference-like instance for a bound method
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target -- the instance-method target for the weak
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reference, must have <im_self> and <im_func> attributes
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and be reconstructable via:
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target.<im_func>.__get__( target.<im_self> )
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which is true of built-in instance methods.
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onDelete -- optional callback which will be called
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when this weak reference ceases to be valid
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(i.e. either the object or the function is garbage
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collected). Should take a single argument,
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which will be passed a pointer to this object.
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"""
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def remove(weak, self=self):
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"""Set self.isDead to true when method or instance is destroyed"""
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methods = self.deletionMethods[:]
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del self.deletionMethods[:]
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try:
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del self.__class__._allInstances[ self.key ]
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except KeyError:
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pass
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for function in methods:
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try:
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if hasattr(function, '__call__' ):
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function( self )
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except Exception as e:
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try:
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traceback.print_exc()
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except AttributeError:
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print('''Exception during saferef %s cleanup function %s: %s'''%(
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self, function, e
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))
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self.deletionMethods = [onDelete]
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self.key = self.calculateKey( target )
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self.weakSelf = weakref.ref(getattr(target,im_self), remove)
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self.weakFunc = weakref.ref(getattr(target,im_func), remove)
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self.selfName = getattr(target,im_self).__class__.__name__
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self.funcName = str(getattr(target,im_func).__name__)
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def calculateKey( cls, target ):
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"""Calculate the reference key for this reference
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Currently this is a two-tuple of the id()'s of the
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target object and the target function respectively.
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"""
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return (id(getattr(target,im_self)),id(getattr(target,im_func)))
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calculateKey = classmethod( calculateKey )
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def __str__(self):
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"""Give a friendly representation of the object"""
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return """%s( %s.%s )"""%(
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self.__class__.__name__,
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self.selfName,
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self.funcName,
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)
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__repr__ = __str__
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def __nonzero__( self ):
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"""Whether we are still a valid reference"""
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return self() is not None
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__bool__ = __nonzero__
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def __cmp__( self, other ):
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"""Compare with another reference"""
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if not isinstance (other,self.__class__):
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return cmp( self.__class__, type(other) )
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return cmp( self.key, other.key)
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def __call__(self):
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"""Return a strong reference to the bound method
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If the target cannot be retrieved, then will
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return None, otherwise returns a bound instance
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method for our object and function.
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Note:
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You may call this method any number of times,
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as it does not invalidate the reference.
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"""
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target = self.weakSelf()
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if target is not None:
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function = self.weakFunc()
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if function is not None:
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return function.__get__(target)
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return None
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