Remove lazy loading of middleware

This mirrors the equivalent change in Django itsef. See:

https://code.djangoproject.com/ticket/26452

99bb7fcc18

channels/handler.py

@@ -7,7 +7,6 @@ import sys
 import time
 import traceback
 from io import BytesIO
-from threading import Lock
 
 from django import http
 from django.conf import settings
@@ -168,20 +167,16 @@ class AsgiHandler(base.BaseHandler):
     a HTTP request)
     """
 
-    initLock = Lock()
     request_class = AsgiRequest
 
     # Size to chunk response bodies into for multiple response messages
     chunk_size = 512 * 1024
 
+    def __init__(self, *args, **kwargs):
+        super(AsgiHandler, self).__init__(*args, **kwargs)
+        self.load_middleware()
+
     def __call__(self, message):
-        # Set up middleware if needed. We couldn't do this earlier, because
-        # settings weren't available.
-        if self._request_middleware is None:
-            with self.initLock:
-                # Check that middleware is still uninitialized.
-                if self._request_middleware is None:
-                    self.load_middleware()
         # Set script prefix from message root_path
         set_script_prefix(message.get('root_path', ''))
         signals.request_started.send(sender=self.__class__, message=message)