def populate(self, installed_apps=None):
        """
        Loads application configurations and models.

        This method imports each application module and then each model module.

        It is thread safe and idempotent, but not reentrant.
        """
        if self.ready:
            return

        # populate() might be called by two threads in parallel on servers
        # that create threads before initializing the WSGI callable.
        with self._lock:
            if self.ready:
                return

            # app_config should be pristine, otherwise the code below won't
            # guarantee that the order matches the order in INSTALLED_APPS.
            if self.app_configs:
                raise RuntimeError("populate() isn't reentrant")

            # Load app configs and app modules.
            for entry in installed_apps:
                if isinstance(entry, AppConfig):
                    app_config = entry
                else:
                    app_config = AppConfig.create(entry)
                if app_config.label in self.app_configs:
                    raise ImproperlyConfigured(
                        "Application labels aren't unique, "
                        "duplicates: %s" % app_config.label)

                self.app_configs[app_config.label] = app_config

            # Check for duplicate app names.
            counts = Counter(
                app_config.name for app_config in self.app_configs.values())
            duplicates = [
                name for name, count in counts.most_common() if count > 1]
            if duplicates:
                raise ImproperlyConfigured(
                    "Application names aren't unique, "
                    "duplicates: %s" % ", ".join(duplicates))

            self.apps_ready = True

            # Load models.
            for app_config in self.app_configs.values():
                all_models = self.all_models[app_config.label]
                app_config.import_models(all_models)

            self.clear_cache()

            self.models_ready = True

            for app_config in self.get_app_configs():
                app_config.ready()

            self.ready = True
dataset/ETHPy150Open django/django/django/apps/registry.py/Apps.populate/original