C#如何通过静态委托提升性能
起因
说是<<String.Create真的快吗?>>的后续,其实关系不是很大,只是使用的代码示例是有关系的,更多的是如何高效使用委托.最近将文章迁移了一部分到今日头条,其中一篇<<写更好的C#代码>>,@Alsein评论在.Net高版本可以使用静态委托,可以避免多余的内存分配,从而提高委托的性能.先看看测试代码
using System;
using System.Buffers;
using BenchmarkDotNet.Attributes;
namespace CSharpBenchmarks.StringTest
{
[MemoryDiagnoser]
[DisassemblyDiagnoser(printSource: true)]
public class StringCreateTest
{
[Params(4096)]
public int Count { get; set; }
public static string OrderNum = "FA210609";
[Benchmark(Baseline = true)]
public void ArrayTest()
{
for (int i = 0; i < Count; i++)
{
Array(OrderNum);
}
}
[Benchmark]
public void CreateTest()
{
for (int i = 0; i < Count; i++)
{
Create(OrderNum);
}
}
[Benchmark]
public void LocalCreateTest()
{
for (int i = 0; i < Count; i++)
{
LocalCreate(OrderNum);
}
}
[Benchmark]
public void StaticCreateTest()
{
for (int i = 0; i < Count; i++)
{
StaticCreate(OrderNum);
}
}
[Benchmark]
public void CreateCaheTest()
{
for (int i = 0; i < Count; i++)
{
CreateCache(OrderNum);
}
}
public string Array(string input)
{
int len = input.Length;
int postion = -1;
char[] arr = new char[len];
for (int i = 0; i < len; i++)
{
if (input[i] >= 'A' && input[i] <= 'Z')
{
arr[i] = input[i];
}
else
{
postion = i;
break;
}
}
if (postion > 0)
{
arr[postion] = 'R';
}
int start = postion + 1;
for (int i = start; i < len; i++)
{
arr[i] = input[i];
}
return new string(arr, 0, len);
}
public string Create(string input)
{
int len = input.Length;
return string.Create(len, input, (target, src) =>
{
int postion = -1;
for (int i = 0; i < len; i++)
{
if (src[i] >= 'A' && src[i] <= 'Z')
{
target[i] = src[i];
}
else
{
postion = i;
break;
}
}
if (postion > 0)
{
target[postion] = 'R';
}
int start = postion + 1;
for (int i = start; i < len; i++)
{
target[i] = src[i];
}
});
}
/// <summary>
/// 减少使用外部变量
/// </summary>
/// <param name="input"></param>
/// <returns></returns>
public string LocalCreate(string input)
{
int len = input.Length;
return string.Create(len, input, (target, src) =>
{
int postion = -1;
int strLen = target.Length;
for (int i = 0; i < strLen; i++)
{
if (src[i] >= 'A' && src[i] <= 'Z')
{
target[i] = src[i];
}
else
{
postion = i;
break;
}
}
if (postion > 0)
{
target[postion] = 'R';
}
int start = postion + 1;
for (int i = start; i < strLen; i++)
{
target[i] = src[i];
}
});
}
/// <summary>
/// 使用静态匿名函数
/// </summary>
/// <param name="input"></param>
/// <returns></returns>
public string StaticCreate(string input)
{
int len = input.Length;
//在委托前加入static关键字修饰,主要避免创建多余的委托对象
//在C# 9加入,静态匿名函数(包含lambda和匿名函数)
return string.Create(len, input, static (target, src) =>
{
int postion = -1;
int strLen = target.Length;
for (int i = 0; i < strLen; i++)
{
if (src[i] >= 'A' && src[i] <= 'Z')
{
target[i] = src[i];
}
else
{
postion = i;
break;
}
}
if (postion > 0)
{
target[postion] = 'R';
}
int start = postion + 1;
for (int i = start; i < strLen; i++)
{
target[i] = src[i];
}
});
}
public void CreateAction(Span<char> target, string src)
{
int postion = -1;
for (int i = 0; i < src.Length; i++)
{
if (src[i] >= 'A' && src[i] <= 'Z')
{
target[i] = src[i];
}
else
{
postion = i;
break;
}
}
if (postion > 0)
{
target[postion] = 'R';
}
int start = postion + 1;
for (int i = start; i < src.Length; i++)
{
target[i] = src[i];
}
}
//给Create所需的委托加缓存,而不是每次都创建新的委托实例
public SpanAction<char, string> spanAction = null;
public string CreateCache(string input)
{
int len = input.Length;
if (spanAction == null) //只有为空的,才会创建委托实例
{
spanAction = CreateAction; //缓存委托实例
}
return string.Create(len, input, spanAction);
}
}
}在使用静态委托,发现是不允许使用作用域外的变量,便调整了代码,增加一个不用static关键字修饰的测试示例,下面看一下性能基准测试结果:
由于基准测试,主要以.Net 5为基线和.Net 6进行对比,结果发现:
- 性能最好的还是缓存委托
- 静态委托和不使用static关键字修饰(不使用作用域外的变量)的要稍慢一下,在反编译源码发现是一样的,为什么静态委托要稍慢一点呢? 有点不太理解.
public string LocalCreate(string input)
{
int num2 = input.get_Length();
string str = input;
SpanAction<char, string> u003cu003e9_120 = StringCreateTest.u003cu003ec.u003cu003e9__12_0;
if (u003cu003e9_120 == null) //看到这里是不是感觉熟悉的套路,只创建一次委托示例对象,和缓存委托是一样,只是由编译器去做
{
u003cu003e9_120 = new SpanAction<char, string>(StringCreateTest.u003cu003ec.u003cu003e9, (Span<char> target, string src) => {
int num = -1;
int length = target.get_Length();
int num1 = 0;
while (num1 < length)
{
if (src[num1] < 'A' || src[num1] > 'Z')
{
num = num1;
break;
}
else
{
*((target.get_Item(num1))) = src[num1];
num1++;
}
}
if (num > 0)
{
*((target.get_Item(num))) = 'R';
}
for (int i = num + 1; i < length; i++)
{
*((target.get_Item(i))) = src[i];
}
});
StringCreateTest.u003cu003ec.u003cu003e9__12_0 = u003cu003e9_120;
}
return string.Create<string>(num2, str, u003cu003e9_120);
}不使用static关键字修饰,在编译时,由编译器自动优化,性能基准测试是随着.Net版本更新,有所不同.
秋风
2021-10-05