name : weakref_finalize.py # -*- coding: utf-8 -*- """ backports.weakref_finalize ~~~~~~~~~~~~~~~~~~ Backports the Python 3 ``weakref.finalize`` method. """ from __future__ import absolute_import import itertools import sys from weakref import ref __all__ = ["weakref_finalize"] class weakref_finalize(object): """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(object): __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) weakref_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 weakref_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 weakref_finalize._dirty: pending = cls._select_for_exit() weakref_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 weakref_finalize._shutdown = True if reenable_gc: gc.enable()