为什么通过 Expression.Call 编译的 lambda 构建比应该执行相同操作的委托稍慢？以及如何避免呢？
解释 BenchmarkDotNet 结果。
我们正在比较CallBuildedReal vs CallLambda;另外两个 CallBuilded 和 CallLambdaConst 是以下的“子形式”CallLambda并显示相同的数字。但区别在于CallBuildedReal具有重要意义。
//[Config(typeof(Config))]
[RankColumn, MinColumn, MaxColumn, StdDevColumn, MedianColumn]
[ClrJob , CoreJob]
[HtmlExporter, MarkdownExporter]
[MemoryDiagnoser /*, InliningDiagnoser*/]
public class BenchmarkCallSimple
{
static Func<StringBuilder, int, int, bool> callLambda;
static Func<StringBuilder, int, int, bool> callLambdaConst;
static Func<StringBuilder, int, int, bool> callBuilded;
static Func<StringBuilder, int, int, bool> callBuildedReal;
private static bool Append<T>(StringBuilder sb, T i1, T i2, Func<T, T, T> operation)
{
sb.Append(operation(i1, i2));
return true;
}
private static Func<StringBuilder, T, T, bool> BuildCallMethod<T>(Func<T, T, T> operation)
{
return (sb, i1, i2)=> { sb.Append(operation(i1, i2)); return true; };
}
private static int AddMethod(int a, int b)
{
return a + b;
}
static BenchmarkCallSimple()
{
var x = Expression.Parameter(typeof(int));
var y = Expression.Parameter(typeof(int));
var additionExpr = Expression.Add(x, y);
callLambdaConst = BuildCallMethod<int>(AddMethod);
callLambda = BuildCallMethod<int>((a, b) => a + b);
var operationDelegate = Expression.Lambda<Func<int, int, int>>(additionExpr, x, y).Compile();
callBuilded = BuildCallMethod(operationDelegate);
var operationExpressionConst = Expression.Constant(operationDelegate, operationDelegate.GetType());
var sb1 = Expression.Parameter(typeof(StringBuilder), "sb");
var i1 = Expression.Parameter(typeof(int), "i1");
var i2 = Expression.Parameter(typeof(int), "i2");
var appendMethodInfo = typeof(BenchmarkCallSimple).GetTypeInfo().GetDeclaredMethod(nameof(BenchmarkCallSimple.Append));
var appendMethodInfoGeneric = appendMethodInfo.MakeGenericMethod(typeof(int));
var appendCallExpression = Expression.Call(appendMethodInfoGeneric,
new Expression[] { sb1, i1, i2, operationExpressionConst }
);
var appendLambda = Expression.Lambda(appendCallExpression, new[] { sb1, i1, i2 });
callBuildedReal = (Func<StringBuilder, int, int, bool>)(appendLambda.Compile());
}
[Benchmark]
public string CallBuildedReal()
{
StringBuilder sb = new StringBuilder();
var b = callBuildedReal(sb, 1, 2);
return sb.ToString();
}
[Benchmark]
public string CallBuilded()
{
StringBuilder sb = new StringBuilder();
var b = callBuilded(sb, 1, 2);
return sb.ToString();
}
[Benchmark]
public string CallLambda()
{
StringBuilder sb = new StringBuilder();
var b = callLambda(sb, 1, 2);
return sb.ToString();
}
[Benchmark]
public string CallLambdaConst()
{
StringBuilder sb = new StringBuilder();
var b = callLambdaConst(sb, 1, 2);
return sb.ToString();
}
}
Results:
BenchmarkDotNet=v0.10.5, OS=Windows 10.0.14393
Processor=Intel Core i5-2500K CPU 3.30GHz (Sandy Bridge), ProcessorCount=4
Frequency=3233539 Hz, Resolution=309.2587 ns, Timer=TSC
[Host] : Clr 4.0.30319.42000, 64bit RyuJIT-v4.6.1648.0
Clr : Clr 4.0.30319.42000, 64bit RyuJIT-v4.6.1648.0
Core : .NET Core 4.6.25009.03, 64bit RyuJIT
Method | Job | Runtime | Mean | Error | StdDev | Min | Max | Median | Rank | Gen 0 | Allocated |
---------------- |----- |-------- |---------:|---------:|---------:|---------:|---------:|---------:|-----:|-------:|----------:|
CallBuildedReal | Clr | Clr | 137.8 ns | 2.903 ns | 4.255 ns | 133.6 ns | 149.6 ns | 135.6 ns | 7 | 0.0580 | 192 B |
CallBuilded | Clr | Clr | 122.7 ns | 2.068 ns | 1.934 ns | 118.5 ns | 126.2 ns | 122.6 ns | 6 | 0.0576 | 192 B |
CallLambda | Clr | Clr | 119.8 ns | 1.342 ns | 1.255 ns | 117.9 ns | 121.7 ns | 119.6 ns | 5 | 0.0576 | 192 B |
CallLambdaConst | Clr | Clr | 121.7 ns | 1.347 ns | 1.194 ns | 120.1 ns | 124.5 ns | 121.6 ns | 6 | 0.0571 | 192 B |
CallBuildedReal | Core | Core | 114.8 ns | 2.263 ns | 2.117 ns | 112.7 ns | 118.8 ns | 113.7 ns | 3 | 0.0594 | 191 B |
CallBuilded | Core | Core | 109.0 ns | 1.701 ns | 1.591 ns | 106.5 ns | 112.2 ns | 108.8 ns | 2 | 0.0599 | 191 B |
CallLambda | Core | Core | 107.0 ns | 1.181 ns | 1.105 ns | 105.7 ns | 109.4 ns | 106.8 ns | 1 | 0.0593 | 191 B |
CallLambdaConst | Core | Core | 117.3 ns | 2.706 ns | 3.704 ns | 113.4 ns | 127.8 ns | 116.0 ns | 4 | 0.0592 | 191 B |
基准代码：
注1：有类似的SO线程“表达式树的性能 https://stackoverflow.com/questions/24802222/performance-of-expression-trees/44233174#44233174“其中构建表达式在基准测试中显示出最佳结果。
注2：当我得到编译表达式的IL代码时，我应该接近答案，所以我正在尝试学习如何获取编译表达式的IL代码（linqpad？，ilasm集成到VS？，动态汇编？），但如果你知道可以在 VS 中完成此操作的简单插件 - 它将对我有很大帮助。
注意3：这不起作用
var assemblyBuilder = System.AppDomain.CurrentDomain.DefineDynamicAssembly(new AssemblyName("testLambda"),System.Reflection.Emit.AssemblyBuilderAccess.Save);
var modelBuilder = assemblyBuilder.DefineDynamicModule("testLambda_module", "testLambda.dll");
var typeBuilder = modelBuilder.DefineType("testLambda_type");
var method = typeBuilder.DefineMethod("testLambda_method", MethodAttributes.Public | MethodAttributes.Static, typeof(bool),
new[] { typeof(StringBuilder), typeof(int), typeof(int), typeof(bool) });
appendLambda.CompileToMethod(method);
typeBuilder.CreateType();
assemblyBuilder.Save("testLambda.dll");
因为系统类型初始化异常：“InvalidOperationException：CompileToMethod无法编译常量'System.Func3[System.Int32,System.Int32,System.Int32]' because it is a non-trivial value, such as a live object. Instead, create an expression tree that can construct this value."
That meansappendLambda` 包含一个 is Func 的参数类型，它不是原始类型，并且 CompileToMethod 存在仅使用原始类型的限制。
