Question

I wrote a simple object copier that copies public properties.
I can’t figure out why the Dynamic method is a lot slower than the c# version.

Durations

C# method : 4,963 ms

Dynamic method : 19,924 ms

Note that – as I run the dynamic method before starting the stopwatch – the duration do not include the compilation phase.
I run that in Debug and Release mode, in x86 and x64 mode, and from VS and from the command line with roughly the same result (dynamic method is 400% slower).

        const int NBRECORDS = 100 * 1000 * 1000;

        public class Person
        {
            private int mSomeNumber;

            public string FirstName { get; set; }
            public string LastName { get; set; }
            public DateTime DateOfBirth { get; set; }
            public int SomeNumber
            {
                get { return mSomeNumber; }
                set { mSomeNumber = value; }
            }
        }

        public static Action<T1, T2> CreateCopier<T1, T2>()
        {
            var meth = new DynamicMethod("copy", null, new Type[] { typeof(T1), typeof(T2) }, restrictedSkipVisibility: true);
            ILGenerator il = meth.GetILGenerator();
            int cpt = 0;

            var stopHere = typeof(Program).GetMethod("StopHere");

            foreach (var mi1 in typeof(T1).GetProperties(BindingFlags.Public | BindingFlags.Instance))
            {
                var mi2 = typeof(T2).GetProperty(mi1.Name, BindingFlags.Public | BindingFlags.Instance);
                if (mi1 != null && mi2 != null)
                {
                    cpt++;
                    il.Emit(OpCodes.Ldarg_1);
                    il.Emit(OpCodes.Ldarg_0);
                    il.Emit(OpCodes.Callvirt, mi1.GetMethod);
                    il.Emit(OpCodes.Callvirt, mi2.SetMethod);
                }
            }
            il.Emit(OpCodes.Ret);

            var dlg = meth.CreateDelegate(typeof(Action<T1, T2>));
            return (Action<T1, T2>)dlg;
        }

        static void Main(string[] args)
        {
            var person1 = new Person() { FirstName = "Pascal", LastName = "Ganaye", DateOfBirth = new DateTime(1909, 5, 1), SomeNumber = 23456 };
            var person2 = new Person();

            var copyUsingAMethod = (Action<Person, Person>)CopyPerson;
            var copyUsingADynamicMethod = CreateCopier<Person, Person>();

            copyUsingAMethod(person1, person2); // 4882 ms
            var sw = Stopwatch.StartNew();
            for (int i = 0; i < NBRECORDS; i++)
            {
                copyUsingAMethod(person1, person2);
            }
            Console.WriteLine("{0} ms", sw.ElapsedMilliseconds);

            copyUsingADynamicMethod(person1, person2); // 19920 ms
            sw = Stopwatch.StartNew();
            for (int i = 0; i < NBRECORDS; i++)
            {
                copyUsingADynamicMethod(person1, person2); 
            }
            Console.WriteLine("{0} ms", sw.ElapsedMilliseconds);


            Console.ReadKey(intercept: true);
        }

        private static void CopyPerson(Person person1, Person person2)
        {
            person2.FirstName = person1.FirstName;
            person2.LastName = person1.LastName;
            person2.DateOfBirth = person1.DateOfBirth;
            person2.SomeNumber = person1.SomeNumber;
        }

From what I can debug the two methods have the same IL code.

IL_0000: nop
IL_0001: ldarg.1
IL_0002: ldarg.0
IL_0003: callvirt   System.String get_FirstName()/DuckCopy.SpeedTests.Program+Person
IL_0008: callvirt   Void set_FirstName(System.String)/DuckCopy.SpeedTests.Program+Person
IL_000d: nop
IL_000e: ldarg.1
IL_000f: ldarg.0
IL_0010: callvirt   System.String get_LastName()/DuckCopy.SpeedTests.Program+Person
IL_0015: callvirt   Void set_LastName(System.String)/DuckCopy.SpeedTests.Program+Person
IL_001a: nop
IL_001b: ldarg.1
IL_001c: ldarg.0
IL_001d: callvirt   System.DateTime get_DateOfBirth()/DuckCopy.SpeedTests.Program+Person
IL_0022: callvirt   Void set_DateOfBirth(System.DateTime)/DuckCopy.SpeedTests.Program+Person
IL_0027: nop
IL_0028: ldarg.1
IL_0029: ldarg.0
IL_002a: callvirt   Int32 get_SomeNumber()/DuckCopy.SpeedTests.Program+Person
IL_002f: callvirt   Void set_SomeNumber(Int32)/DuckCopy.SpeedTests.Program+Person
IL_0034: nop
IL_0035: ret

I applogize if you read this twice.
I posted this originally in: http://www.codeproject.com/Answers/494714/Can-27tplusfigureplusoutpluswhyplusthisplusDynamic
but did not get all the answers I hoped.

edited 17 nov 2012 15:11:

removed the nop
removed the extra ="" which came from I don't where.

Answer 1

This problem was introduced by changes made in .NET Framework 4.0. I found a solution posted by user “Alan-N” on CodeProject.

The big slowdown in execution time is caused when the DynamicMethod gets associated with a “system-provided, fully trusted, security-transparent assembly,” which happens if you use the DynamicMethod(string, Type, Type[], bool) constructor. It appears that .NET 4 is doing more security checks than the previous versions although I have no insight into, or explanation for, what is actually going on.

Associating the DynamicMethod with a Type (by using the DynamicMethod(string, Type, Type[], Type, bool) constructor instead; notice the additional Type-valued parameter, ‘owner’) completely removes the speed penalty.

There are some notes on MSDN which may be relevant (if only I could understand them!):

• DynamicMethod Constructor (String, Type, Type[], Boolean)
• Security Issues in Reflection Emit