Refs #24007 -- Removed an apps.populate() call in model unpickling that can cause deadlocks.

django/db/models/base.py

@@ -1694,8 +1694,6 @@ def model_unpickle(model_id, attrs, factory):
     Used to unpickle Model subclasses with deferred fields.
     """
     if isinstance(model_id, tuple):
-        if not apps.ready:
-            apps.populate(settings.INSTALLED_APPS)
         model = apps.get_model(*model_id)
     else:
         # Backwards compat - the model was cached directly in earlier versions.

docs/releases/1.10.txt

@@ -461,6 +461,16 @@ Since the introduction of migrations for the contrib apps in Django 1.8, the
 tables of these custom user test models were not created anymore making them
 unusable in a testing context.
 
+Apps registry is no longer auto-populated when unpickling models outside of Django
+----------------------------------------------------------------------------------
+
+The apps registry is no longer auto-populated when unpickling models. This was
+added in Django 1.7.2 as an attempt to allow unpickling models outside of
+Django, such as in an RQ worker, without calling ``django.setup()``, but it
+creates the possibility of a deadlock. To adapt your code in the case of RQ,
+you can `provide your own worker script <http://python-rq.org/docs/workers/>`_
+that calls ``django.setup()``.
+
 Miscellaneous
 -------------
 

tests/model_regress/test_pickle.py

@@ -1,17 +1,9 @@
-import datetime
-import os
 import pickle
-import subprocess
-import sys
 
-from django.core.files.temp import NamedTemporaryFile
 from django.db import DJANGO_VERSION_PICKLE_KEY, models
-from django.test import TestCase, mock
-from django.utils._os import npath, upath
+from django.test import TestCase
 from django.utils.version import get_version
 
-from .models import Article
-
 
 class ModelPickleTestCase(TestCase):
     def test_missing_django_version_unpickling(self):
@@ -51,41 +43,3 @@ class ModelPickleTestCase(TestCase):
         msg = "Pickled model instance's Django version 1.0 does not match the current version %s." % get_version()
         with self.assertRaisesMessage(RuntimeWarning, msg):
             pickle.loads(pickle.dumps(p))
-
-    def test_unpickling_when_appregistrynotready(self):
-        """
-        #24007 -- Verifies that a pickled model can be unpickled without having
-        to manually setup the apps registry beforehand.
-        """
-        script_template = """#!/usr/bin/env python
-import pickle
-
-from django.conf import settings
-
-data = %r
-
-settings.configure(DEBUG=False, INSTALLED_APPS=['model_regress'], SECRET_KEY = "blah")
-article = pickle.loads(data)
-print(article.headline)"""
-        a = Article.objects.create(
-            headline="Some object",
-            pub_date=datetime.datetime.now(),
-            article_text="This is an article",
-        )
-
-        with NamedTemporaryFile(mode='w+', suffix=".py") as script:
-            script.write(script_template % pickle.dumps(a))
-            script.flush()
-            # A path to model_regress must be set in PYTHONPATH
-            model_regress_dir = os.path.dirname(upath(__file__))
-            model_regress_path = os.path.abspath(model_regress_dir)
-            tests_path = os.path.split(model_regress_path)[0]
-            pythonpath = os.environ.get('PYTHONPATH', '')
-            pythonpath = npath(os.pathsep.join([tests_path, pythonpath]))
-
-            with mock.patch.dict('os.environ', {'PYTHONPATH': pythonpath}):
-                try:
-                    result = subprocess.check_output([sys.executable, script.name])
-                except subprocess.CalledProcessError:
-                    self.fail("Unable to reload model pickled data")
-        self.assertEqual(result.strip().decode(), "Some object")