Use ActivatorUtlities.CreateFactory instead of CreateInstance (#1643)

* Use ActivatorUtlities.CreateFactory instead of CreateInstance
- Turns out CreateFactory is much much faster
- Added a benchmark for hub activation

benchmarks/Microsoft.AspNetCore.SignalR.Microbenchmarks/DefaultHubActivatorBenchmark.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using BenchmarkDotNet.Attributes;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.AspNetCore.SignalR.Microbenchmarks
+{
+    public class DefaultHubActivatorBenchmark
+    {
+        private DefaultHubActivator<MyHub> _activator;
+
+        [GlobalSetup]
+        public void GlobalSetup()
+        {
+            var services = new ServiceCollection();
+
+            _activator = new DefaultHubActivator<MyHub>(services.BuildServiceProvider());
+        }
+
+        [Benchmark]
+        public int Create()
+        {
+            var hub = _activator.Create();
+            int result = hub.Addition();
+            return result;
+        }
+
+        public class MyHub : Hub
+        {
+            public int Addition()
+            {
+                return 1 + 1;
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.SignalR.Core/DefaultHubActivator.cs

@@ -9,6 +9,8 @@ namespace Microsoft.AspNetCore.SignalR
 {
     public class DefaultHubActivator<THub> : IHubActivator<THub> where THub: Hub
     {
+        // Object factory for THub instances
+        private static readonly Lazy<ObjectFactory> _objectFactory = new Lazy<ObjectFactory>(() => ActivatorUtilities.CreateFactory(typeof(THub), Type.EmptyTypes));
         private readonly IServiceProvider _serviceProvider;
         private bool? _created;
 
@@ -25,7 +27,7 @@ namespace Microsoft.AspNetCore.SignalR
             var hub = _serviceProvider.GetService<THub>();
             if (hub == null)
             {
-                hub = ActivatorUtilities.CreateInstance<THub>(_serviceProvider);
+                hub = (THub)_objectFactory.Value(_serviceProvider, Array.Empty<object>());
                 _created = true;
             }