Faster RequestServices (#941)

* Faster RequestServices

src/Microsoft.AspNetCore.Hosting/Internal/RequestServicesContainerMiddleware.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
@@ -12,7 +13,7 @@ namespace Microsoft.AspNetCore.Hosting.Internal
     public class RequestServicesContainerMiddleware
     {
         private readonly RequestDelegate _next;
-        private IServiceScopeFactory _scopeFactory;
+        private readonly IServiceScopeFactory _scopeFactory;
 
         public RequestServicesContainerMiddleware(RequestDelegate next, IServiceScopeFactory scopeFactory)
         {
@@ -25,37 +26,37 @@ namespace Microsoft.AspNetCore.Hosting.Internal
                 throw new ArgumentNullException(nameof(scopeFactory));
             }
 
-            _scopeFactory = scopeFactory;
             _next = next;
+            _scopeFactory = scopeFactory;
         }
 
         public async Task Invoke(HttpContext httpContext)
         {
-            if (httpContext == null)
+            Debug.Assert(httpContext != null);
-            {
-                throw new ArgumentNullException(nameof(httpContext));
-            }
 
-            var existingFeature = httpContext.Features.Get<IServiceProvidersFeature>();
+            // local cache for virtual disptach result
+            var features = httpContext.Features;
+            var existingFeature = features.Get<IServiceProvidersFeature>();
 
-            // All done if request services is set
+            // All done if RequestServices is set
             if (existingFeature?.RequestServices != null)
             {
                 await _next.Invoke(httpContext);
                 return;
             }
 
-            using (var feature = new RequestServicesFeature(_scopeFactory))
+            var replacementFeature = new RequestServicesFeature(_scopeFactory);
+
+            try
             {
-                try
+                features.Set<IServiceProvidersFeature>(replacementFeature);
-                {
+                await _next.Invoke(httpContext);
-                    httpContext.Features.Set<IServiceProvidersFeature>(feature);
+            }
-                    await _next.Invoke(httpContext);
+            finally
-                }
+            {
-                finally
+                replacementFeature.Dispose();
-                {
+                // Restore previous feature state
-                    httpContext.Features.Set(existingFeature);
+                features.Set(existingFeature);
-                }
             }
         }
     }

src/Microsoft.AspNetCore.Hosting/Internal/RequestServicesFeature.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using Microsoft.AspNetCore.Http.Features;
 using Microsoft.Extensions.DependencyInjection;
 
@@ -9,18 +10,14 @@ namespace Microsoft.AspNetCore.Hosting.Internal
 {
     public class RequestServicesFeature : IServiceProvidersFeature, IDisposable
     {
-        private IServiceScopeFactory _scopeFactory;
+        private readonly IServiceScopeFactory _scopeFactory;
         private IServiceProvider _requestServices;
         private IServiceScope _scope;
         private bool _requestServicesSet;
 
         public RequestServicesFeature(IServiceScopeFactory scopeFactory)
         {
-            if (scopeFactory == null)
+            Debug.Assert(scopeFactory != null);
-            {
-                throw new ArgumentNullException(nameof(scopeFactory));
-            }
-
             _scopeFactory = scopeFactory;
         }