打字性能

它可能是可测量的,如果它正在做数十亿次,而其他工作很少。我不知道clr是否会有效地缓存演员表工作的事实,所以它不需要再这样做-如果现在不这样做,它可能在以后的版本中这样做。它可以在64位的JIT中实现,但不能在32位的版本中实现,反之亦然——你明白了。不过,我怀疑它会对正常代码产生重大影响。

我个人喜欢 可读性 更重要的是,第二种形式。

@我测试了两种方法。这是我在电脑上找到的东西:

他们是关于 相同的 在表演中。实际上,我发现第二种方法稍慢一些。原因(我相信)是额外变量和初始铸造的成本。当然,如果你使用足够的石膏,你可能会得到性能成本回来。看起来你只有在节省20-30次演员后才能在表现上达到收支平衡。

以下是最近两次测试运行的结果:

TestMuliCast\_3x:      00:00:00.5970000   
TestSingleCast\_3x:    00:00:00.6020000   
TestMuliCast\_30x:     00:00:06.0930000   
TestSingleCast\_30x:   00:00:06.0480000   

TestMuliCast\_3x:      00:00:00.6120000   
TestSingleCast\_3x:    00:00:00.6250000   
TestMuliCast\_30x:     00:00:06.5490000   
TestSingleCast\_30x:   00:00:06.4440000   

我还测试了 castclass 和 isinst . 根据我读到的:

http://m3mia.blogspot.com/2007/11/comparing-isinst-to-castclass.html
http://www.codeproject.com/KB/cs/csharpcasts.aspx
http://discuss.joelonsoftware.com/default.asp?dotnet.12.635066.13

我以为ISISINT会比CastClass更快,即使没有例外。然而,在创建了自己的基准之后,我发现 更慢的 比CastClass更重要。非常有趣。以下是我的结果:

TestEmptyLoop:        00:00:00.0870000   
TestDCast\_castclass:  00:00:00.2640000   
TestDCast\_isinst:     00:00:00.3780000   

TestEmptyLoop:        00:00:00.0870000   
TestDCast\_castclass:  00:00:00.2600000   
TestDCast\_isinst:     00:00:00.3750000   

所以,斯基特先生,我接受纠正。

环境:

Windows Vista
最大核心速度3.2GHz
.NET Framework 2.0.50727版

以下是我创建和运行的基准的完整来源: (利用jon skeets微标记框架 here )

using System;   
using System.Collections;

public class CastingBenchmark   
{
    static Int64 Iterations=100000000;
    static Int64 TestWork = 0;

    public static void Init(string[] args)
    {
        if (args.Length>0)
            Iterations = Int64.Parse(args[0]);
    }

    public static void Reset()
    {
        TestWork = 0;
    }

    internal class BaseType { public void TestBaseMethod() { TestWork++; } }

    internal class DerivedType : BaseType { 
        public void TestDerivedMethod() { TestWork++; }
        public void TestDerivedMethod2() { TestWork++; }
        public void TestDerivedMethod3() { TestWork++; } 
}

[Benchmark]
public static void TestMuliCast_3x()
{
    BaseType TestBaseType = new DerivedType();

    for (int x = 0; x < Iterations; x++)
    {
        ((DerivedType)TestBaseType).TestDerivedMethod();
        ((DerivedType)TestBaseType).TestDerivedMethod2();
        ((DerivedType)TestBaseType).TestDerivedMethod3();
    }
}

[Benchmark]
public static void TestSingleCast_3x()
{
    BaseType TestBaseType = new DerivedType();

    for (int x = 0; x < Iterations; x++)
    {
        DerivedType TestDerivedType = (DerivedType)TestBaseType;
        TestDerivedType.TestDerivedMethod();
        TestDerivedType.TestDerivedMethod2();
        TestDerivedType.TestDerivedMethod3();
    }
}

[Benchmark]
public static void TestMuliCast_30x()
{
    BaseType TestBaseType = new DerivedType();

    for (int x = 0; x < Iterations; x++)
    {
        //Simulate 3 x 10 method calls while casting
        for (int y = 0; y < 10; y++) {

            ((DerivedType)TestBaseType).TestDerivedMethod();
            ((DerivedType)TestBaseType).TestDerivedMethod2();
            ((DerivedType)TestBaseType).TestDerivedMethod3();
        }
    }
}

[Benchmark]
public static void TestSingleCast_30x()
{
    BaseType TestBaseType = new DerivedType();

    for (int x = 0; x < Iterations; x++)
    {
        DerivedType TestDerivedType = (DerivedType)TestBaseType;

        //Simulate 3 x 10 method calls on already-cast object
        for (int y = 0; y < 10; y++)
        {
            TestDerivedType.TestDerivedMethod();
            TestDerivedType.TestDerivedMethod2();
            TestDerivedType.TestDerivedMethod3();
        }
    }
}

    [Benchmark]
    public static void TestEmptyLoop()
    {
        for (int x = 0; x < Iterations; x++)
        {
        }
    }

    [Benchmark]
    public static void TestDCast_castclass()
    {
        BaseType TestDerivedType = new DerivedType();

        for (int x = 0; x < Iterations; x++)
        {
            ((DerivedType)TestDerivedType).TestDerivedMethod();
        }    
    }

    [Benchmark]
    public static void TestDCast_isinst()
    {
        BaseType TestDerivedType = new DerivedType();

        for (int x = 0; x < Iterations; x++)
        {
            (TestDerivedType as DerivedType).TestDerivedMethod();
        }
    }
}

以及由此产生的IL 伊辛 和 铸钢类 方法:

method public hidebysig static void TestDCast_isinst() cil managed
{
    .custom instance void BenchmarkAttribute::.ctor()
    .maxstack 2
    .locals init (
        [0] class CastingBenchmark/BaseType TestDerivedType,
        [1] int32 x)
    L_0000: newobj instance void CastingBenchmark/DerivedType::.ctor()
    L_0005: stloc.0 
    L_0006: ldc.i4.0 
    L_0007: stloc.1 
    L_0008: br.s L_0019
    L_000a: ldloc.0 
    L_000b: isinst CastingBenchmark/DerivedType
    L_0010: callvirt instance void CastingBenchmark/DerivedType::TestDerivedMethod()
    L_0015: ldloc.1 
    L_0016: ldc.i4.1 
    L_0017: add 
    L_0018: stloc.1 
    L_0019: ldloc.1 
    L_001a: conv.i8 
    L_001b: ldsfld int64 CastingBenchmark::Iterations
    L_0020: blt.s L_000a
    L_0022: ret 
}

.method public hidebysig static void TestDCast_castclass() cil managed
{
    .custom instance void BenchmarkAttribute::.ctor()
    .maxstack 2
    .locals init (
        [0] class CastingBenchmark/BaseType TestDerivedType,
        [1] int32 x)
    L_0000: newobj instance void CastingBenchmark/DerivedType::.ctor()
    L_0005: stloc.0 
    L_0006: ldc.i4.0 
    L_0007: stloc.1 
    L_0008: br.s L_0019
    L_000a: ldloc.0 
    L_000b: castclass CastingBenchmark/DerivedType
    L_0010: callvirt instance void CastingBenchmark/DerivedType::TestDerivedMethod()
    L_0015: ldloc.1 
    L_0016: ldc.i4.1 
    L_0017: add 
    L_0018: stloc.1 
    L_0019: ldloc.1 
    L_001a: conv.i8 
    L_001b: ldsfld int64 CastingBenchmark::Iterations
    L_0020: blt.s L_000a
    L_0022: ret 
}