性能测试笔记

想比较 as , is , typeof , GetType , 强制类型转换 这几个哪个性能更好。

以下是测试代码：

            object a = "hello";
            Stopwatch sw = Stopwatch.StartNew();
            sw.Restart();
            for (int i = 0; i < 10000; i++)
            {
                var d = a as string;
            }
            Console.WriteLine("As:" + sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < 10000; i++)
            {
                var d = (string)a;
            }
            Console.WriteLine("(string):" + sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < 10000; i++)
            {
                var d = a.GetType();
            }
            Console.WriteLine("GetType:" + sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < 10000; i++)
            {
                var d = typeof(string);
            }
            Console.WriteLine("typeof:" + sw.ElapsedTicks);

            for (int i = 0; i < 10000; i++)
            {
                var d = a is int;
            }
            Console.WriteLine("Is:" + sw.ElapsedTicks);

单元测试下Debug
第一次		第二次		第三次		平均
As:142		As:147		As:160		As:150
Is:157		Is:152		Is:177		Is:162
(string):146		(string):147		(string):165		(string):153
typeof:611		typeof:616		typeof:687		typeof:637
GetType:314		GetType:313		GetType:353		GetType:327
单元测试下Release
第一次		第二次		第三次		平均
As:21		As:20		As:20		As:20
Is:20		Is:20		Is:20		Is:20
(string):98		(string):98		(string):98		(string):98
typeof:20		typeof:20		typeof:20		typeof:20
GetType:333		GetType:333		GetType:348		GetType:339
Console程序Debug
第一次		第二次		第三次		平均
As:183		As:184		As:184		As:184
Is:295		Is:295		Is:411		Is:334
(string):231		(string):177		(string):241		(string):216
typeof:278		typeof:216		typeof:213		typeof:236
GetType:477		GetType:430		GetType:424		GetType:443
Console程序Release
第一次		第二次		第三次		平均
As:11		As:11		As:11		As:11
Is:6		Is:6		Is:6		Is:6
(string):45		(string):45		(string):45		(string):45
typeof:7		typeof:6		typeof:6		typeof:6
GetType:6		GetType:7		GetType:7		GetType:7

单元测试下，性能是不准的。

Release 下性能 比较：  is = typeof 高于 GetType 高于 As  高于 强制类型转换。

 ----------------------------------------------------------

持续对以上结果表示怀疑，增加循环次数。

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using MyCmn;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
using System.Diagnostics;
using System.Threading;
using System.Linq;

namespace Test
{
    public class Main_Cls
    {
        const int TIMES = 100000;
        public static void Main()
        {
            object a = "hello world";
            var str = "hello world!";
            Stopwatch sw = Stopwatch.StartNew();

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = typeof(string);
            }
            MyConsole.WriteLine("typeof:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = a.GetType();
            }
            MyConsole.WriteLine("GetType:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = object.Equals(a, null);
            }
            MyConsole.WriteLine("object.Equals:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = default(string);
            }
            MyConsole.WriteLine("default:", sw.ElapsedTicks);

            MyConsole.WriteLine("String______________");
            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = "hello";
            }
            MyConsole.WriteLine("new string:", sw.ElapsedTicks);
            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = str.Length;
            }
            MyConsole.WriteLine("String.Length:", sw.ElapsedTicks);
            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = string.IsNullOrEmpty(str);
            }
            MyConsole.WriteLine("string.IsNullOrEmpty:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = a as string;
            }
            MyConsole.WriteLine("As:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = a is int;
            }
            MyConsole.WriteLine("Is:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = (string)a;
            }
            MyConsole.WriteLine("(string):", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = i.ToString();
            }
            MyConsole.WriteLine("ToString:", sw.ElapsedTicks);
            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = i.AsString();
            }
            MyConsole.WriteLine("AsString:", sw.ElapsedTicks);


            MyConsole.WriteLine("                            ______________String");
            MyConsole.WriteLine("类型转换______________");

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = DateTime.Now;
            }
            MyConsole.WriteLine("DateTime:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = Guid.NewGuid();
            }
            MyConsole.WriteLine("Guid:", sw.ElapsedTicks);


            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = i.AsDecimal();
            }
            MyConsole.WriteLine("AsDecimal:", sw.ElapsedTicks);

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var d = i.AsFloat();
            }
            MyConsole.WriteLine("AsFloat:", sw.ElapsedTicks);
            MyConsole.WriteLine("                            ______________类型转换");

            sw.Restart();
            for (int i = 0; i < TIMES; i++)
            {
                var t = typeof(string).GetProperties();
            }
            MyConsole.WriteLine("Reflect:", sw.ElapsedTicks);
        }
    }

    public static class MyConsole
    {
        public static void WriteLine(string title, long msg = 0)
        {
            if (msg > 0)
            {
                Console.WriteLine(string.Format("{0,27} {1,-8}", title, msg));
            }
            else
            {
                Console.WriteLine(title);
            }
        }
    }
}

结果：

typeof: 45
GetType: 44
object.Equals: 1620
default: 44
String______________
new string: 45
String.Length: 45
string.IsNullOrEmpty: 900
As: 44
Is: 46
(string): 391
ToString: 53567
AsString: 146645
______________String
类型转换______________
DateTime: 35750
Guid: 69539
AsDecimal: 72932
AsFloat: 289442
______________类型转换
Reflect: 71428

As  的性能略高于 Is , 但 判等的性能却是出忽意料的差。

再加入 == 判定测试 和 a.Equals 的判定测试：

typeof: 58
GetType: 50
object.Equals: 1736
==: 49
a.Equals: 2420
default: 50
String______________
new string: 50
String.Length: 50
string.IsNullOrEmpty: 969
As: 50
Is: 50
(string): 441
ToString: 52179
AsString: 139356
______________String
类型转换______________
DateTime: 35400
Guid: 69725
AsDecimal: 82086
AsFloat: 321944
______________类型转换
Reflect: 63618

查看源码：

public static bool IsNullOrEmpty(string value)
{
    if (value != null)
    {
        return (value.Length == 0);
    }
    return true;
}