Added a context manager to hold the import lock.

"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

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

        # 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:

                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):

        """

from __future__ import absolute_import  # Avoid importing `importlib` from this package.

from contextlib import contextmanager

import copy

import imp

from importlib import import_module

    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