Skip middleware code when there are no user middlewares installed

CHANGES/2629.feature

@@ -0,0 +1 @@
+Fixes performance issue introduced by #2577. When there are no middlewares installed by the user, no additional and useless code is executed.

aiohttp/web_app.py

@@ -110,15 +110,18 @@ def freeze(self):
             return
 
         self._frozen = True
-        self._middlewares = tuple(self._prepare_middleware())
+        self._middlewares.freeze()
         self._router.freeze()
         self._on_response_prepare.freeze()
         self._on_startup.freeze()
         self._on_shutdown.freeze()
         self._on_cleanup.freeze()
+        self._run_middlewares = len(self.middlewares) > 0
+        self._middlewares_handlers = tuple(self._prepare_middleware())
 
         for subapp in self._subapps:
             subapp.freeze()
+            self._run_middlewares |= len(subapp._middlewares) > 0
 
     @property
     def debug(self):
@@ -241,6 +244,7 @@ def _prepare_middleware(self):
                               'see #2252'.format(m),
                               DeprecationWarning, stacklevel=2)
                 yield m, False
+
         yield _fix_request_current_app(self), True
 
     async def _handle(self, request):
@@ -260,12 +264,14 @@ async def _handle(self, request):
 
         if resp is None:
             handler = match_info.handler
-            for app in match_info.apps[::-1]:
-                for m, new_style in app._middlewares:
-                    if new_style:
-                        handler = partial(m, handler=handler)
-                    else:
-                        handler = await m(app, handler)
+
+            if self._run_middlewares:
+                for app in match_info.apps[::-1]:
+                    for m, new_style in app._middlewares_handlers:
+                        if new_style:
+                            handler = partial(m, handler=handler)
+                        else:
+                            handler = await m(app, handler)
 
             resp = await handler(request)
 

tests/test_web_app.py

@@ -195,6 +195,7 @@ def test_app_delitem():
 def test_app_freeze():
     app = web.Application()
     subapp = mock.Mock()
+    subapp._middlewares = ()
     app._subapps.append(subapp)
 
     app.freeze()
@@ -210,3 +211,28 @@ def test_equality():
 
     assert app1 == app1
     assert app1 != app2
+
+
+def test_app_run_middlewares():
+
+    root = web.Application()
+    sub = web.Application()
+    root.add_subapp('/sub', sub)
+    root.freeze()
+    assert root._run_middlewares is False
+
+    @web.middleware
+    async def middleware(request, handler):
+        return await handler(request)
+
+    root = web.Application(middlewares=[middleware])
+    sub = web.Application()
+    root.add_subapp('/sub', sub)
+    root.freeze()
+    assert root._run_middlewares is True
+
+    root = web.Application()
+    sub = web.Application(middlewares=[middleware])
+    root.add_subapp('/sub', sub)
+    root.freeze()
+    assert root._run_middlewares is True