Struct 创建性能大比拼（反射，泛型反射，泛型创建，缓存Emit）
上篇介绍了 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), 在这里做一个总结（执行10万次）
- 直接创建Class对象最快 5ms
- 缓存Emit 6ms (不包含Emit时间）
- 泛型反射147ms
- 泛型创建159ms(其实是编译器的语法糖，内部仍然调用泛型反射）
- 反射340ms
- 非缓存Emit 12786ms
经过上面的对比应该很清楚了Class创建原则：
直接创建->用缓存Emit->泛型反射->泛型创建->反射（反射大约比直接调用慢68倍左右），避免非缓存Emit
这篇就来一个Struct创建性能大比拼。因为Struct和Class一个是值类型一个是引用类型，一个是分配在栈上一个是分配在堆上，用在Class上创建原则未必都和在Struct上的创建原则一致。咱们仍然以代码来说话。
被测试的Struct：
struct TestEntity { }
1. 手工创建
[TestInfo(Category = "Struct.Constructor", Name = "Direct")]
class DirectInvokeMode : IRunable
{
public void Run()
{
new TestEntity();
}
}
2. 反射创建
[TestInfo(Category = "Struct.Constructor", Name = "Reflect")]
class ReflectInvokeMode : IRunable
{
public void Run()
{
Activator.CreateInstance(typeof(TestEntity));
}
}
3. 泛型反射创建
[TestInfo(Category = "Struct.Constructor", Name = "GenericReflect")]
class GenericReflectInvokeMode : IRunable
{
public void Run()
{
Activator.CreateInstance<TestEntity>();
}
}
4. 泛型直接创建
[TestInfo(Category = "Struct.Constructor", Name = "Generic Create")]
class GenericCreateInvokeMode : IRunable
{
public void Run()
{
Create<TestEntity>();
}
static T Create<T>() where T : new()
{
return new T();
}
}
5. 缓存Emit创建：因为结构体没有缺省构造函数，不能用IL 进行emit,这里用ExpressionTree进行Emit
/// <summary>
/// 得到缺省构造函数委托
/// </summary>
/// <param name="type"></param>
/// <returns></returns>
public static DefaultConstructorHandler GetDefaultCreator(this Type type)
{
if(type == Types.String)
{
DefaultConstructorHandler s = ()=>null;
return s;
}
var ctorExpression = Expression.Lambda<DefaultConstructorHandler>(Expression.Convert(Expression.New(type), typeof(object)));
var ctor = ctorExpression.Compile();
DefaultConstructorHandler handler = () =>
{
try
{
return ctor();
}
catch (TargetInvocationException ex)
{
throw ex.InnerException.Handle();
}
catch (Exception ex)
{
throw ex.Handle();
}
};
return handler;
}
基于上面Emit代码进行创建的Struct，代码如下：
[TestInfo(Category = "Struct.Constructor", Name = "Emit")]
class EmitInvokeMode : IRunable
{
//结构体没有缺省构造函数
static readonly DefaultConstructorHandler Ctor = typeof(TestEntity).GetDefaultCreator();
public void Run()
{
Ctor();
}
}
测试函数：
for (int i = 0; i < 3; i++)
{
foreach (var item in Mappers)
CodeTimer.Time(item.Metadata.Category + "->" + item.Metadata.Name, 100000, () => item.Value.Run());
}
输出结果如下：
------ Test started: Assembly: NLite.Test.dll ------ Struct.Constructor->Direct Time Elapsed: 4ms CPU Cycles: 156,250 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Reflect Time Elapsed: 330ms CPU Cycles: 2,968,750 Gen 0: 1 Gen 1: 0 Gen 2: 0 Struct.Constructor->GenericReflect Time Elapsed: 26ms CPU Cycles: 156,250 Gen 0: 1 Gen 1: 0 Gen 2: 0 Struct.Constructor->Generic Create Time Elapsed: 3ms CPU Cycles: 156,250 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Emit Time Elapsed: 7ms CPU Cycles: 0 Gen 0: 1 Gen 1: 0 Gen 2: 0 Struct.Constructor->Direct Time Elapsed: 1ms CPU Cycles: 0 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Reflect Time Elapsed: 329ms CPU Cycles: 3,281,250 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->GenericReflect Time Elapsed: 22ms CPU Cycles: 312,500 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Generic Create Time Elapsed: 4ms CPU Cycles: 156,250 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Emit Time Elapsed: 3ms CPU Cycles: 156,250 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Direct Time Elapsed: 1ms CPU Cycles: 0 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Reflect Time Elapsed: 339ms CPU Cycles: 3,437,500 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->GenericReflect Time Elapsed: 22ms CPU Cycles: 312,500 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Generic Create Time Elapsed: 2ms CPU Cycles: 0 Gen 0: 0 Gen 1: 0 Gen 2: 0 Struct.Constructor->Emit Time Elapsed: 3ms CPU Cycles: 0 Gen 0: 0 Gen 1: 0 Gen 2: 0 1 passed, 0 failed, 0 skipped, took 2.53 seconds (NUnit 2.5.5).
从测试结果可以看出一个非常离奇的问题，泛型创建超过Emit超过泛型反射，这在Class的创建测试中，Emit超过泛型反射，泛型反射超过泛型创建。
