Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/FastDelegateCreator.cs

@@ -0,0 +1,58 @@
+//------------------------------------------------------------------------------
+// <copyright file="FastDelegateCreator.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Reflection;
+    using System.Reflection.Emit;
+    using System.Security.Permissions;
+
+    // Helper utility to quickly create a Delegate by calling its unmanaged ctor
+
+    [SecurityPermission(SecurityAction.LinkDemand, Unrestricted = true)]
+    internal static class FastDelegateCreator<TDelegate> where TDelegate : class {
+
+        private static readonly Func<object, IntPtr, TDelegate> _factory = GetFactory();
+
+        // obj is the 'this' pointer (potentially null)
+        // method is RuntimeMethodHandle.GetFunctionPointer()
+        internal static TDelegate BindTo(object obj, IntPtr method) {
+            return _factory(obj, method);
+        }
+
+        // obj is the 'this' pointer (potentially null)
+        // method is the MethodInfo to bind to
+        internal static TDelegate BindTo(object obj, MethodInfo method) {
+            return BindTo(obj, method.MethodHandle.GetFunctionPointer());
+        }
+
+        // Assert needed since we'll be asked to create delegates to potentially private / protected methods
+        [ReflectionPermission(SecurityAction.Assert, MemberAccess = true)]
+        private static Func<object, IntPtr, TDelegate> GetFactory() {
+            // All delegates have a .ctor(object @object, IntPtr method), but since we can't call this
+            // directly from C# we just need to LCG it.
+            ConstructorInfo delegateCtor = typeof(TDelegate).GetConstructor(new Type[] { typeof(object), typeof(IntPtr) });
+
+            // Define method FastCreateDelegate_X: (object, IntPtr) -> TDelegate
+            DynamicMethod dynamicMethod = new DynamicMethod(
+                name: "FastCreateDelegate_" + typeof(TDelegate).Name,
+                returnType: typeof(TDelegate),
+                parameterTypes: new Type[] { typeof(object), typeof(IntPtr) },
+                owner: typeof(FastDelegateCreator<TDelegate>),
+                skipVisibility: true);
+
+            // return new TDelegate(obj, method);
+            ILGenerator ilGen = dynamicMethod.GetILGenerator();
+            ilGen.Emit(OpCodes.Ldarg_0); // Stack contains ('this')
+            ilGen.Emit(OpCodes.Ldarg_1); // Stack contains ('this', 'method')
+            ilGen.Emit(OpCodes.Newobj, delegateCtor); // Stack contains (delegate)
+            ilGen.Emit(OpCodes.Ret);
+
+            return (Func<object, IntPtr, TDelegate>)dynamicMethod.CreateDelegate(typeof(Func<object, IntPtr, TDelegate>));
+        }
+
+    }
+}