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weakref.py
"""Weak reference support for Python. This module is an implementation of PEP 205: http://www.python.org/dev/peps/pep-0205/ """ # Naming convention: Variables named "wr" are weak reference objects; # they are called this instead of "ref" to avoid name collisions with # the module-global ref() function imported from _weakref. from _weakref import ( getweakrefcount, getweakrefs, ref, proxy, CallableProxyType, ProxyType, ReferenceType, _remove_dead_weakref) from _weakrefset import WeakSet, _IterationGuard import collections # Import after _weakref to avoid circular import. import sys import itertools ProxyTypes = (ProxyType, CallableProxyType) __all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs", "WeakKeyDictionary", "ReferenceType", "ProxyType", "CallableProxyType", "ProxyTypes", "WeakValueDictionary", "WeakSet", "WeakMethod", "finalize"] class WeakMethod(ref): """ A custom `weakref.ref` subclass which simulates a weak reference to a bound method, working around the lifetime problem of bound methods. """ __slots__ = "_func_ref", "_meth_type", "_alive", "__weakref__" def __new__(cls, meth, callback=None): try: obj = meth.__self__ func = meth.__func__ except AttributeError: raise TypeError("argument should be a bound method, not {}" .format(type(meth))) from None def _cb(arg): # The self-weakref trick is needed to avoid creating a reference # cycle. self = self_wr() if self._alive: self._alive = False if callback is not None: callback(self) self = ref.__new__(cls, obj, _cb) self._func_ref = ref(func, _cb) self._meth_type = type(meth) self._alive = True self_wr = ref(self) return self def __call__(self): obj = super().__call__() func = self._func_ref() if obj is None or func is None: return None return self._meth_type(func, obj) def __eq__(self, other): if isinstance(other, WeakMethod): if not self._alive or not other._alive: return self is other return ref.__eq__(self, other) and self._func_ref == other._func_ref return False def __ne__(self, other): if isinstance(other, WeakMethod): if not self._alive or not other._alive: return self is not other return ref.__ne__(self, other) or self._func_ref != other._func_ref return True __hash__ = ref.__hash__ class WeakValueDictionary(collections.MutableMapping): """Mapping class that references values weakly. Entries in the dictionary will be discarded when no strong reference to the value exists anymore """ # We inherit the constructor without worrying about the input # dictionary; since it uses our .update() method, we get the right # checks (if the other dictionary is a WeakValueDictionary, # objects are unwrapped on the way out, and we always wrap on the # way in). def __init__(*args, **kw): if not args: raise TypeError("descriptor '__init__' of 'WeakValueDictionary' " "object needs an argument") self, *args = args if len(args) > 1: raise TypeError('expected at most 1 arguments, got %d' % len(args)) def remove(wr, selfref=ref(self), _atomic_removal=_remove_dead_weakref): self = selfref() if self is not None: if self._iterating: self._pending_removals.append(wr.key) else: # Atomic removal is necessary since this function # can be called asynchronously by the GC _atomic_removal(d, wr.key) self._remove = remove # A list of keys to be removed self._pending_removals = [] self._iterating = set() self.data = d = {} self.update(*args, **kw) def _commit_removals(self): l = self._pending_removals d = self.data # We shouldn't encounter any KeyError, because this method should # always be called *before* mutating the dict. while l: key = l.pop() _remove_dead_weakref(d, key) def __getitem__(self, key): if self._pending_removals: self._commit_removals() o = self.data[key]() if o is None: raise KeyError(key) else: return o def __delitem__(self, key): if self._pending_removals: self._commit_removals() del self.data[key] def __len__(self): if self._pending_removals: self._commit_removals() return len(self.data) def __contains__(self, key): if self._pending_removals: self._commit_removals() try: o = self.data[key]() except KeyError: return False return o is not None def __repr__(self): return "<%s at %#x>" % (self.__class__.__name__, id(self)) def __setitem__(self, key, value): if self._pending_removals: self._commit_removals() self.data[key] = KeyedRef(value, self._remove, key) def copy(self): if self._pending_removals: self._commit_removals() new = WeakValueDictionary() for key, wr in self.data.items(): o = wr() if o is not None: new[key] = o return new __copy__ = copy def __deepcopy__(self, memo): from copy import deepcopy if self._pending_removals: self._commit_removals() new = self.__class__() for key, wr in self.data.items(): o = wr() if o is not None: new[deepcopy(key, memo)] = o return new def get(self, key, default=None): if self._pending_removals: self._commit_removals() try: wr = self.data[key] except KeyError: return default else: o = wr() if o is None: # This should only happen return default else: return o def items(self): if self._pending_removals: self._commit_removals() with _IterationGuard(self): for k, wr in self.data.items(): v = wr() if v is not None: yield k, v def keys(self): if self._pending_removals: self._commit_removals() with _IterationGuard(self): for k, wr in self.data.items(): if wr() is not None: yield k __iter__ = keys def itervaluerefs(self): """Return an iterator that yields the weak references to the values. The references are not guaranteed to be 'live' at the time they are used, so the result of calling the references needs to be checked before being used. This can be used to avoid creating references that will cause the garbage collector to keep the values around longer than needed. """ if self._pending_removals: self._commit_removals() with _IterationGuard(self): yield from self.data.values() def values(self): if self._pending_removals: self._commit_removals() with _IterationGuard(self): for wr in self.data.values(): obj = wr() if obj is not None: yield obj def popitem(self): if self._pending_removals: self._commit_removals() while True: key, wr = self.data.popitem() o = wr() if o is not None: return key, o def pop(self, key, *args): if self._pending_removals: self._commit_removals() try: o = self.data.pop(key)() except KeyError: o = None if o is None: if args: return args[0] else: raise KeyError(key) else: return o def setdefault(self, key, default=None): try: o = self.data[key]() except KeyError: o = None if o is None: if self._pending_removals: self._commit_removals() self.data[key] = KeyedRef(default, self._remove, key) return default else: return o def update(*args, **kwargs): if not args: raise TypeError("descriptor 'update' of 'WeakValueDictionary' " "object needs an argument") self, *args = args if len(args) > 1: raise TypeError('expected at most 1 arguments, got %d' % len(args)) dict = args[0] if args else None if self._pending_removals: self._commit_removals() d = self.data if dict is not None: if not hasattr(dict, "items"): dict = type({})(dict) for key, o in dict.items(): d[key] = KeyedRef(o, self._remove, key) if len(kwargs): self.update(kwargs) def valuerefs(self): """Return a list of weak references to the values. The references are not guaranteed to be 'live' at the time they are used, so the result of calling the references needs to be checked before being used. This can be used to avoid creating references that will cause the garbage collector to keep the values around longer than needed. """ if self._pending_removals: self._commit_removals() return list(self.data.values()) class KeyedRef(ref): """Specialized reference that includes a key corresponding to the value. This is used in the WeakValueDictionary to avoid having to create a function object for each key stored in the mapping. A shared callback object can use the 'key' attribute of a KeyedRef instead of getting a reference to the key from an enclosing scope. """ __slots__ = "key", def __new__(type, ob, callback, key): self = ref.__new__(type, ob, callback) self.key = key return self def __init__(self, ob, callback, key): super().__init__(ob, callback) class WeakKeyDictionary(collections.MutableMapping): """ Mapping class that references keys weakly. Entries in the dictionary will be discarded when there is no longer a strong reference to the key. This can be used to associate additional data with an object owned by other parts of an application without adding attributes to those objects. This can be especially useful with objects that override attribute accesses. """ def __init__(self, dict=None): self.data = {} def remove(k, selfref=ref(self)): self = selfref() if self is not None: if self._iterating: self._pending_removals.append(k) else: del self.data[k] self._remove = remove # A list of dead weakrefs (keys to be removed) self._pending_removals = [] self._iterating = set() self._dirty_len = False if dict is not None: self.update(dict) def _commit_removals(self): # NOTE: We don't need to call this method before mutating the dict, # because a dead weakref never compares equal to a live weakref, # even if they happened to refer to equal objects. # However, it means keys may already have been removed. l = self._pending_removals d = self.data while l: try: del d[l.pop()] except KeyError: pass def _scrub_removals(self): d = self.data self._pending_removals = [k for k in self._pending_removals if k in d] self._dirty_len = False def __delitem__(self, key): self._dirty_len = True del self.data[ref(key)] def __getitem__(self, key): return self.data[ref(key)] def __len__(self): if self._dirty_len and self._pending_removals: # self._pending_removals may still contain keys which were # explicitly removed, we have to scrub them (see issue #21173). self._scrub_removals() return len(self.data) - len(self._pending_removals) def __repr__(self): return "<%s at %#x>" % (self.__class__.__name__, id(self)) def __setitem__(self, key, value): self.data[ref(key, self._remove)] = value def copy(self): new = WeakKeyDictionary() for key, value in self.data.items(): o = key() if o is not None: new[o] = value return new __copy__ = copy def __deepcopy__(self, memo): from copy import deepcopy new = self.__class__() for key, value in self.data.items(): o = key() if o is not None: new[o] = deepcopy(value, memo) return new def get(self, key, default=None): return self.data.get(ref(key),default) def __contains__(self, key): try: wr = ref(key) except TypeError: return False return wr in self.data def items(self): with _IterationGuard(self): for wr, value in self.data.items(): key = wr() if key is not None: yield key, value def keys(self): with _IterationGuard(self): for wr in self.data: obj = wr() if obj is not None: yield obj __iter__ = keys def values(self): with _IterationGuard(self): for wr, value in self.data.items(): if wr() is not None: yield value def keyrefs(self): """Return a list of weak references to the keys. The references are not guaranteed to be 'live' at the time they are used, so the result of calling the references needs to be checked before being used. This can be used to avoid creating references that will cause the garbage collector to keep the keys around longer than needed. """ return list(self.data) def popitem(self): self._dirty_len = True while True: key, value = self.data.popitem() o = key() if o is not None: return o, value def pop(self, key, *args): self._dirty_len = True return self.data.pop(ref(key), *args) def setdefault(self, key, default=None): return self.data.setdefault(ref(key, self._remove),default) def update(self, dict=None, **kwargs): d = self.data if dict is not None: if not hasattr(dict, "items"): dict = type({})(dict) for key, value in dict.items(): d[ref(key, self._remove)] = value if len(kwargs): self.update(kwargs) class finalize: """Class for finalization of weakrefable objects finalize(obj, func, *args, **kwargs) returns a callable finalizer object which will be called when obj is garbage collected. The first time the finalizer is called it evaluates func(*arg, **kwargs) and returns the result. After this the finalizer is dead, and calling it just returns None. When the program exits any remaining finalizers for which the atexit attribute is true will be run in reverse order of creation. By default atexit is true. """ # Finalizer objects don't have any state of their own. They are # just used as keys to lookup _Info objects in the registry. This # ensures that they cannot be part of a ref-cycle. __slots__ = () _registry = {} _shutdown = False _index_iter = itertools.count() _dirty = False _registered_with_atexit = False class _Info: __slots__ = ("weakref", "func", "args", "kwargs", "atexit", "index") def __init__(self, obj, func, *args, **kwargs): if not self._registered_with_atexit: # We may register the exit function more than once because # of a thread race, but that is harmless import atexit atexit.register(self._exitfunc) finalize._registered_with_atexit = True info = self._Info() info.weakref = ref(obj, self) info.func = func info.args = args info.kwargs = kwargs or None info.atexit = True info.index = next(self._index_iter) self._registry[self] = info finalize._dirty = True def __call__(self, _=None): """If alive then mark as dead and return func(*args, **kwargs); otherwise return None""" info = self._registry.pop(self, None) if info and not self._shutdown: return info.func(*info.args, **(info.kwargs or {})) def detach(self): """If alive then mark as dead and return (obj, func, args, kwargs); otherwise return None""" info = self._registry.get(self) obj = info and info.weakref() if obj is not None and self._registry.pop(self, None): return (obj, info.func, info.args, info.kwargs or {}) def peek(self): """If alive then return (obj, func, args, kwargs); otherwise return None""" info = self._registry.get(self) obj = info and info.weakref() if obj is not None: return (obj, info.func, info.args, info.kwargs or {}) @property def alive(self): """Whether finalizer is alive""" return self in self._registry @property def atexit(self): """Whether finalizer should be called at exit""" info = self._registry.get(self) return bool(info) and info.atexit @atexit.setter def atexit(self, value): info = self._registry.get(self) if info: info.atexit = bool(value) def __repr__(self): info = self._registry.get(self) obj = info and info.weakref() if obj is None: return '<%s object at %#x; dead>' % (type(self).__name__, id(self)) else: return '<%s object at %#x; for %r at %#x>' % \ (type(self).__name__, id(self), type(obj).__name__, id(obj)) @classmethod def _select_for_exit(cls): # Return live finalizers marked for exit, oldest first L = [(f,i) for (f,i) in cls._registry.items() if i.atexit] L.sort(key=lambda item:item[1].index) return [f for (f,i) in L] @classmethod def _exitfunc(cls): # At shutdown invoke finalizers for which atexit is true. # This is called once all other non-daemonic threads have been # joined. reenable_gc = False try: if cls._registry: import gc if gc.isenabled(): reenable_gc = True gc.disable() pending = None while True: if pending is None or finalize._dirty: pending = cls._select_for_exit() finalize._dirty = False if not pending: break f = pending.pop() try: # gc is disabled, so (assuming no daemonic # threads) the following is the only line in # this function which might trigger creation # of a new finalizer f() except Exception: sys.excepthook(*sys.exc_info()) assert f not in cls._registry finally: # prevent any more finalizers from executing during shutdown finalize._shutdown = True if reenable_gc: gc.enable()
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