deadlock at load time from register_plugin

[John Bazik]

I'm experiencing deadlock at load time (python manage.py help) due to a nested call to apps.populate in django 1.8.7 and django-cms 3.2.0.  It was suggested to me that the problem lies with register_plugin, which loads templates; that since django 1.7, that should happen in AppConfig.ready().

The detailed description of my problem and responses are here:

https://groups.google.com/forum/#!topic/django-users/WiRzQ8EFOdo

John

[John Bazik]

Hey, so, in that other thread, Shai (of django-dev) said:

> I have never used Django-CMS, but according to your description, it (or its plugins) is doing what
> applications should avoid doing since Django 1.7 and the app-loading refactor. Registrations which
> involve interactions with applications -- and loading templates falls under this definition -- should
> happen only in an app's AppConfig.ready(), after all the models are already loaded.

The problem is in plugin_pool.register_plugin.  In validating the plugin, it invokes the template
loader stack, and if any third party loaders are in there, they can, for instance (in my case)
attempt to retrieve a model from cache before all the models are loaded.

If you agree that this is a problem, how about splitting registration and validation of plugins and
doing the former at load time and the latter in cms.apps.CMSConfig.ready()?  I can offer a patch
if you're okay with the concept.

John

[Iacopo Spalletti]

Thanks for the time investigating this.
Given that I overlooked that part when doing the 1.7 migration, I guess
it's up to me to fix this :)
See https://github.com/divio/django-cms/pull/4946

Tests may fail due to unrelated change in classytags. The code being the
same in 3.1/3.2 I opened PR on 3.1, but it should apply cleanly on 3.2 too

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Iacopo Spalletti

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