Thread safe bound method weakrefs

[German M. Bravo]

I'm often getting this traceback:

AttributeError: 'BoundMethodWeakref' object has no attribute 'deletionMethods'

Stacktrace (most recent call last):

  File "django/core/handlers/base.py", line 119, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "posts/views.py", line 404, in get
    posts_post.save()
  File "django/db/models/base.py", line 475, in save
    self.save_base(using=using, force_insert=force_insert, force_update=force_update)
  File "django/db/models/base.py", line 506, in save_base
    signals.pre_save.send(sender=origin, instance=self, raw=raw, using=using)
  File "django/dispatch/dispatcher.py", line 183, in send
    response = receiver(signal=self, sender=sender, **named)
  File "haystack/models.py", line 268, in load_indexes
    ui.setup_indexes()
  File "haystack/utils/loading.py", line 283, in setup_indexes
    index._setup_save()
  File "celery_haystack/indexes.py", line 33, in _setup_save
    signals.post_save.connect(self._enqueue_save, sender=model, dispatch_uid=CelerySearchIndex)
  File "django/dispatch/dispatcher.py", line 105, in connect
    receiver = saferef.safeRef(receiver, onDelete=self._remove_receiver)
  File "django/dispatch/saferef.py", line 29, in safeRef
    onDelete=onDelete
  File "django/dispatch/saferef.py", line 248, in get_bound_method_weakref
    return BoundMethodWeakref(target=target, onDelete=onDelete)
  File "django/dispatch/saferef.py", line 88, in __new__
    current.deletionMethods.append( onDelete)

I suspect this has something to do with the threading environment I'm using. I'm attaching a patch that I believe fixes the issue.

[Florian Apolloner]

Did you attach the wrong patch here?

[Florian Apolloner]

Wth did the resolution get set to fixed :/

[Aymeric Augustin]

This may be a valid issue, but the description doesn't include enough information to reproduce it and the wrong patch was attached.

[German M. Bravo]

Sorry I attached the wrong file, I've just attached the correct one.

The problem seems to be the BoundMethodWeakref._allInstances is filled with an uninitialised object, and when/if another thread tries to get and use the object right away, it doesn't still have at least the deletionMethods attribute which is added during the call to __init__().

[Anssi Kääriäinen]

The explanation seems correct to me. It also seems this will be impossible to test. You will need to switch to another thread in between the dict assignment and the __init__() call, and then you need to access the same key in another thread. An unlikely scenario.

[Marc Tamlyn]

Our implementation of weakrefs has now gone in favour of (backported) code from python 3.4. This should hopefully no longer be an issue.