1

我在 Windows 10 64 位操作系统上使用 .net core 2.0.5。每次，我都会使用 string.Concat 或 string.Format 连接字符串，因为我了解到使用字符串“abc”+“def”的性能更差。（内存使用是一个不同的话题。） - 我最近对字符串连接进行了基准测试，但结果非常有趣；


using System;

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Attributes.Columns;
using BenchmarkDotNet.Attributes.Exporters;

namespace TryBenchmark.ConsoleApp.Benchmarks
{
    [RPlotExporter, RankColumn]
    public class StringConcatVsStringFormat
    {
        [Benchmark]
        public void StringConcat001()
        {
            string result = "test1 " + "test2 " + "test3";

            if (result != "test1 test2 test3")
            {
                throw new InvalidOperationException("Tests are faulty !");
            }
        }

        [Benchmark]
        public void StringConcat002()
        {
            string result = String.Concat("test1 ", "test2 ", "test3");

            if (result != "test1 test2 test3")
            {
                throw new InvalidOperationException("Tests are faulty !");
            }
        }

        [Benchmark]
        public void StringConcat003()
        {
            string name1 = "test1";
            string name2 = "test2";
            string name3 = "test3";

            string result = $"{name1} {name2} {name3}";

            if (result != "test1 test2 test3")
            {
                throw new InvalidOperationException("Tests are faulty !");
            }
        }

        [Benchmark]
        public void StringFormat()
        {
            string result = String.Format("{0} {1} {2}", "test1", "test2", "test3");

            if (result != "test1 test2 test3")
            {
                throw new InvalidOperationException("Tests are faulty !");
            }
        }
    }
}

结果; 


StringConcatVsStringFormat.StringFormat: DefaultJob
Runtime = .NET Core 2.0.5 (CoreCLR 4.6.26020.03, CoreFX 4.6.26018.01), 64bit RyuJIT; GC = Concurrent Workstation
Mean = 149.2378 ns, StdErr = 0.9310 ns (0.62%); N = 79, StdDev = 8.2749 ns
Min = 140.0365 ns, Q1 = 143.8430 ns, Median = 145.9400 ns, Q3 = 150.4091 ns, Max = 172.1811 ns
IQR = 6.5661 ns, LowerFence = 133.9939 ns, UpperFence = 160.2582 ns
ConfidenceInterval = [146.0541 ns; 152.4215 ns] (CI 99.9%), Margin = 3.1837 ns (2.13% of Mean)
Skewness = 1.29, Kurtosis = 3.57, MValue = 2
-------------------- Histogram --------------------
[139.525 ns ; 142.434 ns) | @@@@@@@@@@@
[142.434 ns ; 145.809 ns) | @@@@@@@@@@@@@@@@@@@@@@@@@@@@
[145.809 ns ; 150.658 ns) | @@@@@@@@@@@@@@@@@@@@@@
[150.658 ns ; 156.460 ns) | @@@@
[156.460 ns ; 160.840 ns) | @
[160.840 ns ; 164.215 ns) | @@@@@@@
[164.215 ns ; 169.531 ns) | @@@@
[169.531 ns ; 173.869 ns) | @@
---------------------------------------------------

Total time: 00:03:26 (206.65 sec)

// * Summary *

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.16299.248 (1709/FallCreatorsUpdate/Redstone3)
Intel Core i7-7500U CPU 2.70GHz (Kaby Lake), 1 CPU, 4 logical and 2 physical cores
Frequency=2835939 Hz, Resolution=352.6169 ns, Timer=TSC
.NET Core SDK=2.1.100
  [Host]     : .NET Core 2.0.5 (CoreCLR 4.6.26020.03, CoreFX 4.6.26018.01), 64bit RyuJIT  [AttachedDebugger]
  DefaultJob : .NET Core 2.0.5 (CoreCLR 4.6.26020.03, CoreFX 4.6.26018.01), 64bit RyuJIT


          Method |       Mean |     Error |    StdDev |      Median | Rank |
---------------- |-----------:|----------:|----------:|------------:|-----:|
 StringConcat001 |   1.043 ns | 0.0608 ns | 0.1558 ns |   0.9972 ns |    1 |
 StringConcat002 |  26.680 ns | 0.5303 ns | 0.5445 ns |  26.7079 ns |    2 |
 StringConcat003 | 143.028 ns | 2.4180 ns | 2.2618 ns | 143.9356 ns |    3 |
    StringFormat | 149.238 ns | 3.1837 ns | 8.2749 ns | 145.9400 ns |    4 |

// * Warnings *
Environment
  Summary -> Benchmark was executed with attached debugger

StringConcat001 怎么最快？
难道我做错了什么？还是我错误配置了 benchmarkdotnet？

4

1 回答 1

4

C# 编译器足够聪明，可以检测到 的值string result = "test1 " + "test2 " + "test3";是一个常量。

您可以使用 ILSpy 查看编译器生成的内容：

[Benchmark]
public void StringConcat001()
{
    if (!("test1 test2 test3" != "test1 test2 test3"))
    {
        return;
    }
    throw new InvalidOperationException("Tests are faulty !");
}

要欺骗编译器，您要么必须将这些值放入公共的非只读字段，要么将它们用作给定方法的参数。BenchmarkDotNet0.10.14允许您提供值作为参数。

[RPlotExporter, RankColumn]
[MarkdownExporterAttribute.StackOverflow]
[MemoryDiagnoser]
public class StringConcatVsStringFormat
{
    [Benchmark]
    [Arguments("test1 ", "test2 ", "test3")]
    public string StringConcat001(string arg1, string arg2, string arg3)
        => arg1 + arg2 + arg3;

    [Benchmark]
    [Arguments("test1 ", "test2 ", "test3")]
    public string StringConcat002(string arg1, string arg2, string arg3)
        => String.Concat(arg1, arg2, arg3);

    [Benchmark]
    [Arguments("test1 ", "test2 ", "test3")]
    public string StringConcat003(string arg1, string arg2, string arg3)
        => $"{arg1} {arg2} {arg3}";

    [Benchmark]
    [Arguments("test1 ", "test2 ", "test3")]
    public string StringFormat(string arg1, string arg2, string arg3)
        => string.Format("{0} {1} {2}", arg1, arg2, arg3);
}

在我的电脑上给出以下结果：

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.16299.309 (1709/FallCreatorsUpdate/Redstone3)
Intel Xeon CPU E5-1650 v4 3.60GHz, 1 CPU, 12 logical and 6 physical cores
Frequency=3507503 Hz, Resolution=285.1031 ns, Timer=TSC
  [Host]     : .NET Framework 4.7.1 (CLR 4.0.30319.42000), 32bit LegacyJIT-v4.7.2633.0
  DefaultJob : .NET Framework 4.7.1 (CLR 4.0.30319.42000), 32bit LegacyJIT-v4.7.2633.0


          Method |   arg1 |   arg2 |  arg3 |      Mean |     Error |    StdDev | Rank |  Gen 0 | Allocated |
---------------- |------- |------- |------ |----------:|----------:|----------:|-----:|-------:|----------:|
 StringConcat001 | test1  | test2  | test3 |  25.95 ns | 0.1755 ns | 0.1642 ns |    2 | 0.0091 |      48 B |
 StringConcat002 | test1  | test2  | test3 |  25.66 ns | 0.3480 ns | 0.3085 ns |    1 | 0.0091 |      48 B |
 StringConcat003 | test1  | test2  | test3 | 112.32 ns | 0.9539 ns | 0.8923 ns |    4 | 0.0098 |      52 B |
    StringFormat | test1  | test2  | test3 | 111.62 ns | 0.9982 ns | 0.8849 ns |    3 | 0.0098 |      52 B |
于 2018-04-10T10:36:55.493 回答