利用表达式树构建委托改善反射性能

最近搞一个系统时由于在比较关键地方用到反射了，所以要关注了一下反射的性能问题。搜索一下，不难搜到老赵的这篇文章，下面是一些杂乱的笔记。（建议先看老赵的文章）

.Net4.0反射性能改善

看老赵的文章，老赵得到的结果是这样的：

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00:00:00.0125539 (Directly invoke)
00:00:04.5349626 (Reflection invoke)
00:00:00.0322555 (Dynamic executor)

而我把代码搞下来自己运行得到这样的结果：

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00:00:00.0009710 (Directly invoke)
00:00:00.4142893 (Reflection invoke)
00:00:00.0194501 (Dynamic executor)

这里不是说机器性能造成绝对的时间，而是差距比例完全不一样，想了一阵想起了老赵当时应该是基于.Net3.5，果断把程序的目标框架切换到.Net3.5，结果如下：

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00:00:00.0018801 (Directly invoke)
00:00:02.4288876 (Reflection invoke)
00:00:00.0141537 (Dynamic executor)
三者的差距仍然有些不一样，老赵那边的直接调用与动态执行同一数量级的结果还是没有。但发现了另一些信息。反射和直接调用方法.Net4.0比.Net3.5有非常大的改善，特别是反射，性能提升了好几倍。反而构建表达式树动态调用的方式性能比.Net3.5差了一点。但是相对反射还是有差距，按照这个比例，写写表达式树还是值得的。

改善老赵的DynamicMethodExecutor

老赵的那篇的文章的思路是使用DynamicMethodExecutor来构造一个万能的委托Func<object, object[],="" object=""><object, object[], object>其中第一个参数是实例对象，第二是参数列表，第三是返回值。.Net4.0的表达式树要比3.5的先进一点，经过一番改造发现是不需要这么一个万能委托的，直接用Expression.Lambda.Compile()编译出来的Delegate强制转换为强类型的委托来得更加简单。全部代码一个方法即可，精简了许多。

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/// <summary>
/// 动态构造委托
/// </summary>
/// <param name="methodInfo">方法元数据</param>
/// <returns>委托</returns>
public static Delegate BuildDynamicDelegate(MethodInfo methodInfo)
{
    if (methodInfo == null)
        throw new ArgumentNullException("methodInfo");
 
    var paramExpressions = methodInfo.GetParameters().Select((p, i) =>
    {
        var name = "param" + (i + 1).ToString(CultureInfo.InvariantCulture);
        return Expression.Parameter(p.ParameterType, name);
    }).ToList();
 
    MethodCallExpression callExpression;
    if (methodInfo.IsStatic)
    {
        //Call(params....)
        callExpression = Expression.Call(methodInfo, paramExpressions);
    }
    else
    {
        var instanceExpression = Expression.Parameter(methodInfo.ReflectedType, "instance");
        //insatnce.Call(params….)
        callExpression = Expression.Call(instanceExpression, methodInfo, paramExpressions);
        paramExpressions.Insert(0, instanceExpression);
    }
    var lambdaExpression = Expression.Lambda(callExpression, paramExpressions);
    return lambdaExpression.Compile();
}

使用时转换为强类型的委托即可：

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var action = (Action<TInstance, T1, T2>)BuildDynamicDelegate(methodInfo);
var func = (Func<TInstance, T1, T2, TReturn>)BuildDynamicDelegate(methodInfo);

老赵那个委托都是object，使用时的类型转换，还有装箱，拆箱都会有一定的性能损失，而强类型就没有这个问题。

首先在老赵的那篇文章上一个方法改为两个方法，然后测试：

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public void Call1(object o1, object o2, object o3) { }
public void Call2(int o1, int o2, int o3) { }
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private static void DynamicExecutor_ObjectType()
{
    var executor = new DynamicMethodExecutor(Call1MethodInfo);
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i < Times; i++)
    {
        executor.Execute(ProgramInstance, ObjectParameters);
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Dynamic executor(object))(JeffreyZhao)");
}
private static void DynamicExecutor_IntType()
{
    var executor = new DynamicMethodExecutor(Call2MethodInfo);
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i < Times; i++)
    {
        executor.Execute(ProgramInstance, IntParameters);
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Dynamic executor(int))(JeffreyZhao)");
}
private static void DynamicExecutor_StrongObject()
{
    var action = DynamicMethodBuilder.BuildAction<Program, object, object, object>(Call1MethodInfo);
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i < Times; i++)
    {
        action(ProgramInstance, ObjectParameters[0], ObjectParameters[1], ObjectParameters[2]);
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Dynamic executor(object))(zhangweiwen)");
}
 
private static void DynamicExecutor_StrongInt()
{
    var action = DynamicMethodBuilder.BuildAction<Program, int, int, int>(Call2MethodInfo);
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i < Times; i++)
    {
        action(ProgramInstance, IntParameters1[0], IntParameters1[1], IntParameters1[2]);
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Dynamic executor(int))(zhangweiwen)");
}

结果：

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00:00:00.0188422 (Dynamic executor(object))(JeffreyZhao)
00:00:00.0210869 (Dynamic executor(int))(JeffreyZhao)
00:00:00.0142841 (Dynamic executor(object))(zhangweiwen)
00:00:00.0147589 (Dynamic executor(int))(zhangweiwen)

差距不大，但是还是有一定得改善，特别参数是int的方法，用了强类型后性能比较稳定，不会出现偏差。

构建委托动态赋值

既然有动态调用方法，同样也可以动态赋值，而且据我的经验，根据PropertyInfo的SetValue去反射设属性值用得比反射调用方法更加频繁。所以同样需要有方法来动态构建委托改善性能。

幸好，.Net4.0提供了支持，.Net4.0新增了Expression.Assign来表示一个赋值表达式。有了它，构建起来比方法的更加简单：

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private static Action<TInstance, TProperty> BuildSetPropertyAction<TInstance, TProperty>(PropertyInfo propertyInfo)
{
    var instanceParam = Expression.Parameter(typeof(TInstance), "instance");
    var valueParam = Expression.Parameter(typeof(TProperty), "value");
    //instance.Property
    var propertyProperty = Expression.Property(instanceParam, propertyInfo);
    //instance.Property = value
    var assignExpression = Expression.Assign(propertyProperty, valueParam);
    var lambdaExpression = Expression.Lambda<Action<TInstance, TProperty>>(assignExpression, instanceParam, valueParam);
    return lambdaExpression.Compile();
}

直接返回了强类型的委托，所以使用起来更加简单：

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var action = BuildSetPropertyAction<Program, object>(ObjectPropertyInfo);
action(ProgramInstance, ObjectValue);

来测试一下性能：

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private static void DirectlySetValueType()
{
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i &lt; Times; i++)
    {
        ProgramInstance.IntProperty = IntValue;
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Directly Set IntProperty)");
}
 
private static void ReflectionSetValueType()
{
    var watch2 = new Stopwatch();
    watch2.Start();
    for (var i = 0; i &lt; Times; i++)
    {
        IntPropertyInfo.SetValue(ProgramInstance, IntValue, null);
    }
    watch2.Stop();
    Console.WriteLine(watch2.Elapsed + " (Reflection Set IntProperty)");
}
 
private static void DynamicSetValueType()
{
    var action = BuildSetPropertyAction&lt;Program, int&gt;(IntPropertyInfo);
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i &lt; Times; i++)
    {
        action(ProgramInstance, IntValue);
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Dynamic Set IntProperty)");
}
 
private static void DirectlySetReferenceType()
{
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i &lt; Times; i++)
    {
        ProgramInstance.ObjectProperty = ObjectValue;
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Directly Set ObjectProperty)");
}
 
private static void ReflectionSetReferenceType()
{
    var watch2 = new Stopwatch();
    watch2.Start();
    for (var i = 0; i &lt; Times; i++)
    {
        ObjectPropertyInfo.SetValue(ProgramInstance, ObjectValue, null);
    }
    watch2.Stop();
    Console.WriteLine(watch2.Elapsed + " (Reflection Set ObjectProperty)");
}
 
private static void DynamicSetReferenceType()
{
    var action = BuildSetPropertyAction&lt;Program, object&gt;(ObjectPropertyInfo);
    //action(ProgramInstance, ObjectValue);
    var watch1 = new Stopwatch();
    watch1.Start();
    for (var i = 0; i &lt; Times; i++)
    {
        action(ProgramInstance, ObjectValue);
    }
    watch1.Stop();
    Console.WriteLine(watch1.Elapsed + " (Dynamic Set ObjectProperty)");
}

结果如下：

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Test Set Value：
00:00:00.0003237 (Directly Set IntProperty)
00:00:00.3160570 (Reflection Set IntProperty)
00:00:00.0132668 (Dynamic Set IntProperty)
-----
00:00:00.0028183 (Directly Set ObjectProperty)
00:00:00.2937783 (Reflection Set ObjectProperty)
00:00:00.0150118 (Dynamic Set ObjectProperty)

虽然跟直接赋值不能比，但比反射快大概30倍。

全部代码

希望对大家有帮助

The End。

 http://www.cnblogs.com/lemontea/archive/2013/02/04/2891281.html

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原文地址：https://www.cnblogs.com/Leo_wl/p/2891839.html