Fixed #30619 -- Made runserver --nothreading use single threaded WSGIServer.

Browsers often use multiple connections with Connection: keep-alive.
If --nothreading is specified, the WSGI server cannot accept new
connections until the old connection is closed, causing hangs.

Force Connection: close when --nothreading option is used.

tests/servers/tests.py

@@ -9,7 +9,9 @@ from urllib.error import HTTPError
 from urllib.parse import urlencode
 from urllib.request import urlopen
 
+from django.core.servers.basehttp import WSGIServer
 from django.test import LiveServerTestCase, override_settings
+from django.test.testcases import LiveServerThread, QuietWSGIRequestHandler
 
 from .models import Person
 
@@ -50,6 +52,15 @@ class LiveServerAddress(LiveServerBase):
         self.assertEqual(self.live_server_url_test[0], self.live_server_url)
 
 
+class LiveServerSingleThread(LiveServerThread):
+    def _create_server(self):
+        return WSGIServer((self.host, self.port), QuietWSGIRequestHandler, allow_reuse_address=False)
+
+
+class SingleThreadLiveServerTestCase(LiveServerTestCase):
+    server_thread_class = LiveServerSingleThread
+
+
 class LiveServerViews(LiveServerBase):
     def test_protocol(self):
         """Launched server serves with HTTP 1.1."""
@@ -162,6 +173,32 @@ class LiveServerViews(LiveServerBase):
             self.assertIn(b"QUERY_STRING: 'q=%D1%82%D0%B5%D1%81%D1%82'", f.read())
 
 
+@override_settings(ROOT_URLCONF='servers.urls')
+class SingleTreadLiveServerViews(SingleThreadLiveServerTestCase):
+    available_apps = ['servers']
+
+    def test_closes_connection_with_content_length(self):
+        """
+        Contrast to
+        LiveServerViews.test_keep_alive_on_connection_with_content_length().
+        Persistent connections require threading server.
+        """
+        conn = HTTPConnection(
+            SingleTreadLiveServerViews.server_thread.host,
+            SingleTreadLiveServerViews.server_thread.port,
+            timeout=1,
+        )
+        try:
+            conn.request('GET', '/example_view/', headers={'Connection': 'keep-alive'})
+            response = conn.getresponse()
+            self.assertTrue(response.will_close)
+            self.assertEqual(response.read(), b'example view')
+            self.assertEqual(response.status, 200)
+            self.assertEqual(response.getheader('Connection'), 'close')
+        finally:
+            conn.close()
+
+
 class LiveServerDatabase(LiveServerBase):
 
     def test_fixtures_loaded(self):