From 73c9e65b75cd956410ae71f39fb2f6a9b7b45b42 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Wed, 18 Dec 2013 10:34:20 +0100
Subject: [PATCH] Added a context manager to hold the import lock.

---
 django/core/apps/cache.py      |  8 ++------
 django/utils/module_loading.py | 13 +++++++++++++
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/django/core/apps/cache.py b/django/core/apps/cache.py
index b076fc1968..d07c3bbe34 100644
--- a/django/core/apps/cache.py
+++ b/django/core/apps/cache.py
@@ -1,7 +1,6 @@
 "Utilities for loading models and the modules that contain them."
 
 from collections import OrderedDict
-import imp
 from importlib import import_module
 import os
 import sys
@@ -9,7 +8,7 @@ import warnings
 
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
-from django.utils.module_loading import module_has_submodule
+from django.utils.module_loading import import_lock, module_has_submodule
 from django.utils._os import upath
 from django.utils import six
 
@@ -74,8 +73,7 @@ class AppCache(object):
         # without holding the importer lock and another thread then tries to
         # import something which also launches the app loading. For details of
         # this situation see #18251.
-        imp.acquire_lock()
-        try:
+        with import_lock():
             if self.loaded:
                 return
             for app_name in settings.INSTALLED_APPS:
@@ -86,8 +84,6 @@ class AppCache(object):
                 for app_name in self.postponed:
                     self.load_app(app_name)
                 self.loaded = True
-        finally:
-            imp.release_lock()
 
     def load_app(self, app_name, can_postpone=False):
         """
diff --git a/django/utils/module_loading.py b/django/utils/module_loading.py
index 8868a2d3ab..0c6bad2a7b 100644
--- a/django/utils/module_loading.py
+++ b/django/utils/module_loading.py
@@ -1,5 +1,6 @@
 from __future__ import absolute_import  # Avoid importing `importlib` from this package.
 
+from contextlib import contextmanager
 import copy
 import imp
 from importlib import import_module
@@ -35,6 +36,18 @@ def import_by_path(dotted_path, error_prefix=''):
     return attr
 
 
+@contextmanager
+def import_lock():
+    """
+    Context manager that aquires the import lock.
+    """
+    imp.acquire_lock()
+    try:
+        yield
+    finally:
+        imp.release_lock()
+
+
 def autodiscover_modules(*args, **kwargs):
     """
     Auto-discover INSTALLED_APPS modules and fail silently when