Use PooledContextFactory

Also needs aspnet/HttpAbstractions#501 to be
real

Author: benaadams

src/Benchmarks/DebugInfoPageMiddleware.cs

@@ -48,7 +48,6 @@ public async Task Invoke(HttpContext httpContext)
                 await httpContext.Response.WriteAsync($"<li>Configuration: {_configurationName}</li>");
                 await httpContext.Response.WriteAsync($"<li>Server: {_hostingEnv.Configuration["server"]}</li>");
                 await httpContext.Response.WriteAsync($"<li>Server URLs: {_hostingEnv.Configuration["server.urls"]}</li>");
-                await httpContext.Response.WriteAsync($"<li>Supports Send File: {httpContext.Response.SupportsSendFile()}</li>");
 
                 await httpContext.Response.WriteAsync($"<li>Server features:<ul>");
 

src/Benchmarks/Startup.cs

@@ -2,12 +2,15 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
 using System;
+using System.Collections.Generic;
 using System.Data.Common;
 using System.Data.SqlClient;
 using Benchmarks.Data;
 using Microsoft.AspNet.Builder;
 using Microsoft.AspNet.Hosting;
 using Microsoft.AspNet.Http;
+using Microsoft.AspNet.Http.Features;
+using Microsoft.AspNet.Http.Internal;
 using Microsoft.Data.Entity;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -44,6 +47,7 @@ public void ConfigureServices(IServiceCollection services)
             // No scenarios covered by the benchmarks require the HttpContextAccessor so we're replacing it with a
             // no-op version to avoid the cost.
             services.AddSingleton(typeof(IHttpContextAccessor), typeof(InertHttpContextAccessor));
+            services.AddSingleton(typeof(IHttpContextFactory), typeof(PooledContextFactory));
 
             if (StartupOptions.EnableDbTests)
             {
@@ -121,5 +125,44 @@ public class Options
 
             public string ConnectionString { get; set; }
         }
+
+        public class PooledContextFactory : IHttpContextFactory
+        {
+            [ThreadStatic]
+            Queue<HttpContext> _contextPool;
+
+            private Queue<HttpContext> ContextPool
+            {
+                get
+                {
+                    if (_contextPool == null)
+                    {
+                        _contextPool = new Queue<HttpContext>(16);
+                    }
+                    return _contextPool;
+                }
+            }
+
+            public HttpContext Create(IFeatureCollection featureCollection)
+            {
+                if (ContextPool.Count > 0)
+                {
+                    var context = ContextPool.Dequeue();
+                    // Needs https://github.com/aspnet/HttpAbstractions/pull/501
+                    // context.ReplaceFeatures(featureCollection);
+                    return context;
+                }
+
+                return new DefaultHttpContext(featureCollection);
+            }
+
+            public void Dispose(HttpContext httpContext)
+            {
+                if (ContextPool.Count < 16)
+                {
+                    ContextPool.Enqueue(httpContext);
+                }
+            }
+        }
     }
 }