Use dynamically compiled factory instead of Activator.CreateInstance in TypedClientBuilder

src/SignalR/perf/Microbenchmarks/TypedClientBuilderBenchmark.cs

@@ -0,0 +1,31 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Threading;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+using Microsoft.AspNetCore.SignalR.Internal;
+
+namespace Microsoft.AspNetCore.SignalR.Microbenchmarks
+{
+    public class TypedClientBuilderBenchmark
+    {
+        private static readonly IClientProxy Dummy = new DummyProxy();
+
+        [Benchmark]
+        public ITestClient Build()
+        {
+            return TypedClientBuilder<ITestClient>.Build(Dummy);
+        }
+
+        public interface ITestClient { }
+
+        private class DummyProxy : IClientProxy
+        {
+            public Task SendCoreAsync(string method, object[] args, CancellationToken cancellationToken = default)
+            {
+                return Task.CompletedTask;
+            }
+        }
+    }
+}

src/SignalR/server/Core/src/Internal/TypedClientBuilder.cs

@@ -20,6 +20,10 @@ internal static class TypedClientBuilder<T>
 
         private static readonly PropertyInfo CancellationTokenNoneProperty = typeof(CancellationToken).GetProperty("None", BindingFlags.Public | BindingFlags.Static);
 
+        private static readonly ConstructorInfo ObjectConstructor = typeof(object).GetConstructors().Single();
+
+        private static readonly Type[] ParameterTypes = new Type[] { typeof(IClientProxy) };
+
         public static T Build(IClientProxy proxy)
         {
             return _builder.Value(proxy);
@@ -40,20 +44,24 @@ private static Func<IClientProxy, T> GenerateClientBuilder()
             var moduleBuilder = assemblyBuilder.DefineDynamicModule(ClientModuleName);
             var clientType = GenerateInterfaceImplementation(moduleBuilder);
 
-            return proxy => (T)Activator.CreateInstance(clientType, proxy);
+            var factoryMethod = clientType.GetMethod(nameof(Build), BindingFlags.Public | BindingFlags.Static);
+            return (Func<IClientProxy, T>)factoryMethod.CreateDelegate(typeof(Func<IClientProxy, T>));
         }
 
         private static Type GenerateInterfaceImplementation(ModuleBuilder moduleBuilder)
         {
-            var type = moduleBuilder.DefineType(
-                ClientModuleName + "." + typeof(T).Name + "Impl",
-                TypeAttributes.Public,
-                typeof(Object),
-                new[] { typeof(T) });
+            var name = ClientModuleName + "." + typeof(T).Name + "Impl";
+
+            var type = moduleBuilder.DefineType(name, TypeAttributes.Public, typeof(object), new[] { typeof(T) });
+
+            var proxyField = type.DefineField("_proxy", typeof(IClientProxy), FieldAttributes.Private | FieldAttributes.InitOnly);
 
-            var proxyField = type.DefineField("_proxy", typeof(IClientProxy), FieldAttributes.Private);
+            var ctor = BuildConstructor(type, proxyField);
 
-            BuildConstructor(type, proxyField);
+            // Because a constructor doesn't return anything, it can't be wrapped in a
+            // delegate directly, so we emit a factory method that just takes the IClientProxy,
+            // invokes the constructor (using newobj) and returns the new instance of type T.
+            BuildFactoryMethod(type, ctor);
 
             foreach (var method in GetAllInterfaceMethods(typeof(T)))
             {
@@ -79,27 +87,23 @@ private static IEnumerable<MethodInfo> GetAllInterfaceMethods(Type interfaceType
             }
         }
 
-        private static void BuildConstructor(TypeBuilder type, FieldInfo proxyField)
+        private static ConstructorInfo BuildConstructor(TypeBuilder type, FieldInfo proxyField)
         {
-            var method = type.DefineMethod(".ctor", System.Reflection.MethodAttributes.Public | System.Reflection.MethodAttributes.HideBySig);
+            var ctor = type.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, ParameterTypes);
 
-            var ctor = typeof(object).GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
-                null, new Type[] { }, null);
-
-            method.SetReturnType(typeof(void));
-            method.SetParameters(typeof(IClientProxy));
-
-            var generator = method.GetILGenerator();
+            var generator = ctor.GetILGenerator();
 
             // Call object constructor
             generator.Emit(OpCodes.Ldarg_0);
-            generator.Emit(OpCodes.Call, ctor);
+            generator.Emit(OpCodes.Call, ObjectConstructor);
 
             // Assign constructor argument to the proxyField
             generator.Emit(OpCodes.Ldarg_0); // type
             generator.Emit(OpCodes.Ldarg_1); // type proxyfield
             generator.Emit(OpCodes.Stfld, proxyField); // type.proxyField = proxyField
             generator.Emit(OpCodes.Ret);
+
+            return ctor;
         }
 
         private static void BuildMethod(TypeBuilder type, MethodInfo interfaceMethodInfo, FieldInfo proxyField)
@@ -187,6 +191,17 @@ private static void BuildMethod(TypeBuilder type, MethodInfo interfaceMethodInfo
             generator.Emit(OpCodes.Ret); // Return the Task returned by 'invokeMethod'
         }
 
+        private static void BuildFactoryMethod(TypeBuilder type, ConstructorInfo ctor)
+        {
+            var method = type.DefineMethod(nameof(Build), MethodAttributes.Public | MethodAttributes.Static, CallingConventions.Standard, typeof(T), ParameterTypes);
+
+            var generator = method.GetILGenerator();
+
+            generator.Emit(OpCodes.Ldarg_0); // Load the IClientProxy argument onto the stack
+            generator.Emit(OpCodes.Newobj, ctor); // Call the generated constructor with the proxy
+            generator.Emit(OpCodes.Ret); // Return the typed client
+        }
+
         private static void VerifyInterface(Type interfaceType)
         {
             if (!interfaceType.IsInterface)
@@ -206,7 +221,7 @@ private static void VerifyInterface(Type interfaceType)
 
             foreach (var method in interfaceType.GetMethods())
             {
-                VerifyMethod(interfaceType, method);
+                VerifyMethod(method);
             }
 
             foreach (var parent in interfaceType.GetInterfaces())
@@ -215,7 +230,7 @@ private static void VerifyInterface(Type interfaceType)
             }
         }
 
-        private static void VerifyMethod(Type interfaceType, MethodInfo interfaceMethod)
+        private static void VerifyMethod(MethodInfo interfaceMethod)
         {
             if (interfaceMethod.ReturnType != typeof(Task))
             {