Class 创建性能大比拼（反射，泛型反射，泛型创建，缓存Emit，非缓存Emit）

　　一说到反射，很多人都想到了性能，更有甚者直接说“慎用反射，遗患无穷”，“用反射，感觉怎么像是退步啊～”，看到这种言论，直接把反射妖魔化了，如果这种言论长此以往，势必会对很多对反射初学者造成负面影响。反射是一把双刃剑，看你怎样使用了，下面我就用代码说话。

class TestEntity { }

　　1. 手工创建TestEntity 

 [TestInfo(Category = "Class.Constructor", Name = "Direct")]
class DirectInvokeMode:IRunable
 {
public void Run()
 {
new TestEntity();
 }
 }

     2. 反射创建TestEntity 

[TestInfo(Category = "Class.Constructor", Name = "Reflect")]
class ReflectInvokeMode : IRunable
 {
public void Run()
 {
 Activator.CreateInstance(typeof(TestEntity));
 }
 }

　　3. 泛型反射创建TestEntity

[TestInfo(Category = "Class.Constructor", Name = "GenericReflect")]
class GenericReflectInvokeMode : IRunable
 {
public void Run()
 {
 Activator.CreateInstance<TestEntity>();
 }
 }

　　4. Generic 直接创建

[TestInfo(Category = "Class.Constructor", Name = "Generic Create")]
class GenericCreateInvokeMode : IRunable
 {
public void Run()
 {
 Create<TestEntity>();
 }

static T Create<T>() where T : new()
 {
return new T();
 }
 }

5. Emit创建

[TestInfo(Category = "Class.Constructor", Name = "Emit")]
class EmitInvokeMode : IRunable
 {
static readonly ConstructorHandler Ctor = typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator();

public void Run()
 {
 Ctor();
 }
 }

　　6. 不缓存Emit的创建

[TestInfo(Category = "Class.Constructor", Name = "NoCacheEmit")]
class NoCacheEmitInvokeMode : IRunable
 {
public void Run()
 {
typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator()();
 }
 }

　　测试程序：（执行10万次创建Class对象）

foreach (var item in Mappers)
 CodeTimer.Time(item.Metadata.Category + "->" + item.Metadata.Name, 100000, () => item.Value.Run());

输出结果：

------ Test started: Assembly: NLite.Test.dll ------


Class.Constructor->Direct
 Time Elapsed: 5ms
 CPU Cycles: 0
 Gen 0: 1
 Gen 1: 0
 Gen 2: 0

Class.Constructor->Reflect
 Time Elapsed: 320ms
 CPU Cycles: 2,968,750
 Gen 0: 1
 Gen 1: 0
 Gen 2: 0

Class.Constructor->GenericReflect
 Time Elapsed: 147ms
 CPU Cycles: 1,250,000
 Gen 0: 1
 Gen 1: 0
 Gen 2: 0

Class.Constructor->Generic Create
 Time Elapsed: 159ms
 CPU Cycles: 1,406,250
 Gen 0: 1
 Gen 1: 0
 Gen 2: 0

Class.Constructor->Emit
 Time Elapsed: 6ms
 CPU Cycles: 0
 Gen 0: 2
 Gen 1: 0
 Gen 2: 0

Class.Constructor->NoCacheEmit
 Time Elapsed: 12,786ms
 CPU Cycles: 119,218,750
 Gen 0: 162
 Gen 1: 81
 Gen 2: 0

1 passed, 0 failed, 0 skipped, took 67.77 seconds (NUnit 2.5.5).

　　性能比较结果应该是一目了然了！

      附上源代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using NUnit.Framework;
using System.Reflection;
using NLite.Reflection;namespace NLite.Test.Reflection
{[Contract]public interface IRunable{void Run();}//测试器元数据public interface ITestInfo{//目录string Category { get; }//名称string Name { get; }}//映射器元数据注解[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)][MetadataAttributeAttribute]public class TestInfoAttribute : ComponentAttribute{public string Category { get; set; }public string Name { get; set; }}[TestFixture]public class SpecBase{public SpecBase(){}[SetUp]public void SetUp(){Given();When();}public virtual void Given() { }public virtual void When(){}[Test]public void Test(){}}public abstract class PerformanceSpecBase : SpecBase{[InjectMany]protected Lazy<IRunable, ITestInfo>[] Mappers;protected abstract void RegisterComponents();public virtual int Times{get { return 100000; }}public override void Given(){RegisterComponents();ServiceRegistry.Compose(this);}public override void When(){for (int i = 0; i < 3; i++){foreach (var item in Mappers)CodeTimer.Time(item.Metadata.Category + "->" + item.Metadata.Name, Times, () => item.Value.Run());}}}public class InvokeConstructorPerformanceSpec : PerformanceSpecBase{class TestEntity { }protected override void RegisterComponents(){ServiceRegistry.Register<DirectInvokeMode>().Register<ReflectInvokeMode>().Register<GenericReflectInvokeMode>().Register <GenericCreateInvokeMode>().Register<EmitInvokeMode>().Register < NoCacheEmitInvokeMode>().Register < GenericReflectInvokeMode2>();}[TestInfo(Category = "Class.Constructor", Name = "Direct")]class DirectInvokeMode:IRunable{public void Run(){new TestEntity();}}[TestInfo(Category = "Class.Constructor", Name = "Reflect")]class ReflectInvokeMode : IRunable{public void Run(){Activator.CreateInstance(typeof(TestEntity));}}[TestInfo(Category = "Class.Constructor", Name = "GenericReflect")]class GenericReflectInvokeMode : IRunable{public void Run(){Activator.CreateInstance<TestEntity>();}}[TestInfo(Category = "Class.Constructor", Name = "Reflect->Reflect")]class GenericReflectInvokeMode2 : IRunable{static readonly MethodInfo CreateMethod = typeof(Activator).GetMethod("CreateInstance", Type.EmptyTypes).MakeGenericMethod(typeof(TestEntity));public void Run(){CreateMethod.Invoke(null,null);}}[TestInfo(Category = "Class.Constructor", Name = "Generic Create")]class GenericCreateInvokeMode : IRunable{public void Run(){Create<TestEntity>();}static T Create<T>() where T : new(){return new T();}}[TestInfo(Category = "Class.Constructor", Name = "Emit")]class EmitInvokeMode : IRunable{static readonly ConstructorHandler Ctor = typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator();public void Run(){Ctor();}}[TestInfo(Category = "Class.Constructor", Name = "NoCacheEmit")]class NoCacheEmitInvokeMode : IRunable{public void Run(){typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator()();}}}}

      最后给大家一个思考题：Struct 创建性能大比拼的结果是怎样的？（注意Struct是值类型，Class是引用类型，值类型是分配在栈上的，引用类型是分配在堆上的）