Le blog de Thibaud :-): octobre 2010

Abstract

I need to access property value on a object with Reflection API. It is very useful to create for example a generic Deep Clone API on POCO object.

BUT :

Sometimes, Setter method of the object is not public.
I need the very very high performance to do it.
It seems the better way to do is Deletage.CreateDelegate method but it is important to use Invoke() method on it. DynamicMethod is very poor performance approach.
I don’t want use IL approach because it is too hard to develop and maintains.

I propose helper based PropertyInfo, which support the interface IPropertyAccessor. This interface has a method GetValue and SetValue.

A solution

I create a small helper to encapsulate a delegate in generic decorator that’s support my own IPropertyAccessor interface :

IPropertyAccessor Interface is simple :

    public interface IPropertyAccessor
    {
        PropertyInfo PropertyInfo { get; }
        string Name { get; }
        object GetValue(object source)
        void SetValue(object source, object value);
    }

An example :

// UneClasse : a simple class with an Int property PropertyA
var c = new UneClasse();
c.PropertyA= 12345;
PropertyInfo piA = typeof(UneClasse).GetProperty("PropertyA");
var paA = PropertyInfoHelper.GetFastAccessor(piA);
Assert.AreEqual(c.FieldA, 12345); // Ok !
Assert.AreEqual(piA.GetValue(c, null), 12345); // Ok !
Assert.AreEqual(paA.GetValue(c), 12345); // Ok !
paA.SetValue(c, 54321);
Assert.AreEqual(c.PropertyA, 54321); // Ok !
Assert.AreEqual(piA.GetValue(c, null), 54321); // Ok !
Assert.AreEqual(paA.GetValue(c), 54321); // Ok !

Performance

Some tests show importants differences between differences approachs.

NB : all duration is done with 100 000 call on my computer.

Direct call :	~4 ms.
PropertyInfo.SetValue on public setter	~300 ms.
PropertyInfo.SetValue on private setter	~1400 ms.
Stronged delegate on SetValue MethodInfo (Private or public)	~5 ms.
Delegate call with DynamicInvoke (Private or public)	~1500 ms.
IPropertyAccessor helper	~9 ms.

the better way, of course, is direct call : (4 ms)

myInstance.PropertyA = 1234;

Use SetValue method on PropertyInfo (282 ms) (Setter is public)

PropertyInfo piA = typeof(UneClasse).GetProperty("PropertyA");
…
piA.SetValue(myInstance, 1234, null);

Use SetValue method on PropertyInfo (1391 ms) (Setter is private)

Use strong typed Delegate created with Delegate.CreateDelegate() : 4 ms !! (same of direct call and even if Setter is private)

var setMethodA = piA.GetSetMethod(true);
var _setHandlerATyped = (SetValueHandler<UneClasse,int>)Delegate.CreateDelegate(typeof(SetValueHandler<UneClasse,int>),
setMethodA);
…
_setHandlerATyped.Invoke(myInstance, 1234)

Use my helper : 9 ms !!

IPropertyAccessor paA = PropertyInfoHelper.GetFastAccessor(piA);
…
paA.SetValue(myInstance, 1234)

Compare “CreateDelegate” versus “dynamic IL” during intialisation process

in System.Web.dll, you can find an internal class “System.Web.Util.FastPropertyAccessor”.This class use Emit functions to generate dynamic assembly and dynamic code.

I compare this approach (with little reflection to acces internal members) with CreateDelegate approach in console application and 5000 Test class with One property.

The result is :

	IL Approach (System.Web.Util .FastPropertyAccessor)	CreateDelegate Approach (IPropertyAccessor)
Duration	11920 ms.	1337 ms.
Memory delta	~32300 Ko	~6000 Ko

The code of the helper

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;

namespace Tools.Reflection
{
    /// 
    /// Représentation d'une propriété pour accélerer de maniére considérable les écritures/lectures par reflection
    /// sur les propriétés d'un object
    /// 

    public interface IPropertyAccessor
    {
        /// 
        /// La propriété concernée
        /// 

        PropertyInfo PropertyInfo { get; }
        /// 
        /// Le nom de cette propriété
        /// 

        string Name { get; }
        /// 
        /// Récupération de la valeur de la propriété
        /// 

        /// l'object concerné
        /// valeur de la propriété
        object GetValue(object source);

        /// 
        /// Mise en place d'une nouvelle valeur dans la propriété
        /// 

        /// l'object concerné
        /// la nouvelle valeur pour la propriété
        void SetValue(object source, object value);

    }

    /// 
    /// Classe helper pour obtenir l'accesseur sur une propriété donnée
    /// 

    public static class PropertyInfoHelper
    {
        private static Dictionary _cache = new Dictionary();
        /// 
        /// Obtention du helper pour acceder au getter/setter de la propriété
        /// 

        /// 
        /// 
        public static IPropertyAccessor GetFastAccessor(PropertyInfo propertyInfo)
        {
            IPropertyAccessor result;
            lock (_cache)
            {
                if (!_cache.TryGetValue(propertyInfo, out result))
                {
                    result = CreateAccessor(propertyInfo);
                    _cache.Add(propertyInfo, result); ;
                }
            }
            return result;
        }

        /// 
        /// public pour les tests de performances
        /// 

        /// 
        /// 
        public static IPropertyAccessor CreateAccessor(PropertyInfo propertyInfo)
        {
            return (IPropertyAccessor)Activator.CreateInstance(
                        typeof(PropertyWrapper<,>).MakeGenericType
                           (propertyInfo.DeclaringType, propertyInfo.PropertyType), propertyInfo);
        }
    }

    /// 
    /// Classe concrete implémentant IPropertyAccessor
    /// 

    /// 
    /// 
    internal class PropertyWrapper : IPropertyAccessor
    {
        private PropertyInfo _propertyInfo;

        private Func _getMethod;
        private Action _setMethod;

        /// 
        /// Constructeur public
        /// 

        /// la propriété à encapsulé
        public PropertyWrapper(PropertyInfo propertyInfo)
        {
            _propertyInfo = propertyInfo;

            MethodInfo mGet = propertyInfo.GetGetMethod(true);
            MethodInfo mSet = propertyInfo.GetSetMethod(true);

             // Rq : on peut par se biais acceder aussi aux accesseur privé
            //      tous les aspects liés à la sécurité est donc pris en charge par CreateDelegate
            //      et non à chaque appel à GetMethod/SetMethod

            _getMethod = (Func)Delegate.CreateDelegate
                    (typeof(Func), mGet);
            _setMethod = (Action)Delegate.CreateDelegate
                    (typeof(Action), mSet);
        }

        object IPropertyAccessor.GetValue(object source)
        {
            return _getMethod((TObject)source);
        }
        void IPropertyAccessor.SetValue(object source, object value)
        {
            _setMethod((TObject)source, (TValue)value);
        }

        /// 
        /// Voir 
        /// 

        public string Name
        {
            get
            {
                return _propertyInfo.Name;
            }
        }

        /// 
        /// Voir 
        /// 

        public PropertyInfo PropertyInfo
        {
            get
            {
                return _propertyInfo;
            }
        }

    }

}