Class Finalize

Lib/multiprocessing/util.py:253–336

Class which supports object finalization using weakrefs

class Finalize(object):
    '''
    Class which supports object finalization using weakrefs
    '''
    def __init__(self, obj, callback, args=(), kwargs=None, exitpriority=None):
        if (exitpriority is not None) and not isinstance(exitpriority,int):
            raise TypeError(
                "Exitpriority ({0!r}) must be None or int, not {1!s}".format(
                    exitpriority, type(exitpriority)))

        if obj is not None:
            self._weakref = weakref.ref(obj, self)
        elif exitpriority is None:
            raise ValueError("Without object, exitpriority cannot be None")

        self._callback = callback
        self._args = args
        self._kwargs = kwargs or {}
        self._key = (exitpriority, next(_finalizer_counter))
        self._pid = os.getpid()

        _finalizer_registry[self._key] = self

    def __call__(self, wr=None,
                 # Need to bind these locally because the globals can have
                 # been cleared at shutdown
                 _finalizer_registry=_finalizer_registry,
                 sub_debug=sub_debug, getpid=os.getpid):
        '''
        Run the callback unless it has already been called or cancelled
        '''
        try:
            del _finalizer_registry[self._key]
        except KeyError:
            sub_debug('finalizer no longer registered')
        else:
            if self._pid != getpid():
                sub_debug('finalizer ignored because different process')
                res = None
            else:
                sub_debug('finalizer calling %s with args %s and kwargs %s',
                          self._callback, self._args, self._kwargs)
                res = self._callback(*self._args, **self._kwargs)
            self._weakref = self._callback = self._args = \
                            self._kwargs = self._key = None
            return res

    def cancel(self):
        '''
        Cancel finalization of the object
        '''
        try:
            del _finalizer_registry[self._key]
        except KeyError:
            pass
        else:
            self._weakref = self._callback = self._args = \
                            self._kwargs = self._key = None