155 lines
5.2 KiB
Python
155 lines
5.2 KiB
Python
# -*- coding: utf-8 -*-
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"""
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backports.weakref_finalize
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~~~~~~~~~~~~~~~~~~
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Backports the Python 3 ``weakref.finalize`` method.
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"""
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from __future__ import absolute_import
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import itertools
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import sys
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from weakref import ref
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__all__ = ["weakref_finalize"]
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class weakref_finalize(object):
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"""Class for finalization of weakrefable objects
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finalize(obj, func, *args, **kwargs) returns a callable finalizer
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object which will be called when obj is garbage collected. The
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first time the finalizer is called it evaluates func(*arg, **kwargs)
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and returns the result. After this the finalizer is dead, and
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calling it just returns None.
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When the program exits any remaining finalizers for which the
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atexit attribute is true will be run in reverse order of creation.
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By default atexit is true.
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"""
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# Finalizer objects don't have any state of their own. They are
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# just used as keys to lookup _Info objects in the registry. This
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# ensures that they cannot be part of a ref-cycle.
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__slots__ = ()
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_registry = {}
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_shutdown = False
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_index_iter = itertools.count()
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_dirty = False
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_registered_with_atexit = False
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class _Info(object):
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__slots__ = ("weakref", "func", "args", "kwargs", "atexit", "index")
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def __init__(self, obj, func, *args, **kwargs):
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if not self._registered_with_atexit:
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# We may register the exit function more than once because
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# of a thread race, but that is harmless
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import atexit
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atexit.register(self._exitfunc)
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weakref_finalize._registered_with_atexit = True
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info = self._Info()
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info.weakref = ref(obj, self)
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info.func = func
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info.args = args
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info.kwargs = kwargs or None
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info.atexit = True
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info.index = next(self._index_iter)
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self._registry[self] = info
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weakref_finalize._dirty = True
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def __call__(self, _=None):
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"""If alive then mark as dead and return func(*args, **kwargs);
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otherwise return None"""
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info = self._registry.pop(self, None)
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if info and not self._shutdown:
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return info.func(*info.args, **(info.kwargs or {}))
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def detach(self):
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"""If alive then mark as dead and return (obj, func, args, kwargs);
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otherwise return None"""
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info = self._registry.get(self)
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obj = info and info.weakref()
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if obj is not None and self._registry.pop(self, None):
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return (obj, info.func, info.args, info.kwargs or {})
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def peek(self):
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"""If alive then return (obj, func, args, kwargs);
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otherwise return None"""
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info = self._registry.get(self)
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obj = info and info.weakref()
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if obj is not None:
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return (obj, info.func, info.args, info.kwargs or {})
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@property
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def alive(self):
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"""Whether finalizer is alive"""
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return self in self._registry
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@property
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def atexit(self):
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"""Whether finalizer should be called at exit"""
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info = self._registry.get(self)
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return bool(info) and info.atexit
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@atexit.setter
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def atexit(self, value):
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info = self._registry.get(self)
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if info:
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info.atexit = bool(value)
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def __repr__(self):
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info = self._registry.get(self)
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obj = info and info.weakref()
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if obj is None:
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return "<%s object at %#x; dead>" % (type(self).__name__, id(self))
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else:
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return "<%s object at %#x; for %r at %#x>" % (
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type(self).__name__,
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id(self),
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type(obj).__name__,
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id(obj),
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)
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@classmethod
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def _select_for_exit(cls):
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# Return live finalizers marked for exit, oldest first
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L = [(f, i) for (f, i) in cls._registry.items() if i.atexit]
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L.sort(key=lambda item: item[1].index)
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return [f for (f, i) in L]
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@classmethod
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def _exitfunc(cls):
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# At shutdown invoke finalizers for which atexit is true.
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# This is called once all other non-daemonic threads have been
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# joined.
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reenable_gc = False
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try:
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if cls._registry:
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import gc
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if gc.isenabled():
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reenable_gc = True
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gc.disable()
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pending = None
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while True:
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if pending is None or weakref_finalize._dirty:
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pending = cls._select_for_exit()
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weakref_finalize._dirty = False
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if not pending:
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break
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f = pending.pop()
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try:
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# gc is disabled, so (assuming no daemonic
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# threads) the following is the only line in
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# this function which might trigger creation
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# of a new finalizer
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f()
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except Exception:
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sys.excepthook(*sys.exc_info())
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assert f not in cls._registry
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finally:
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# prevent any more finalizers from executing during shutdown
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weakref_finalize._shutdown = True
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if reenable_gc:
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gc.enable()
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