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Looking for a small immutable dictionary with better performance

2020-11-08 19:28:17 Newbe36524

Dictionary Is a very common key value pair management data structure . But in the case of demanding performance , Dictionary search speed is not high . therefore , We need a faster solution .

Requirement specification

here , We need a PropertyInfo The mapping relationship corresponding to the delegate , So we can store 《 Looking for better performance dynamics Getter and Setter programme 》 Commission referred to .

therefore , This dictionary has these features :

  1. Once this dictionary is created, it doesn't need to be modified .
  2. There are not many dictionary items , Because usually one class There won't be too many attributes .

Solutions that

programme 1,Switch Expression method . Use expressions to generate a containing switch case Statement delegation .

programme 2, Array skip table . We know ,switch case The reason why it is more than continuous if else The reason to be fast is because it generates IL Contains a skip table algorithm . therefore , If we have a way to use consecutive numbers as subscripts , And an array . You can go to C# In the implementation of their own jump table .

Knowledge points

  1. Create a delegate using an expression
  2. PropertyInfo There is one int MetadataToken attribute , According to current observation , You can know the properties in a type and its MetadataToken It seems to be continuous , Therefore, it can be used as a skip table after taking the module key.
  3. The so-called skip watch , It can be simply understood as , Use the subscript of the array to locate a specific element in the array .

Implementation code

here , Let's go straight to the code used in the benchmark .

among :

  • Directly Direct reading , No search
  • ArrayIndex Array skip table
  • SwitchExp Expression generation Switch programme
  • Dic Traditional dictionary scheme
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using BenchmarkDotNet.Attributes;

namespace Newbe.ObjectVisitor.BenchmarkTest
{
    [Config(typeof(Config))]
    public class FuncSearchTest
    {
        private Func<Yueluo, object>[] _target;
        private readonly Yueluo _yueluo;
        private readonly Func<Yueluo, string> _func;
        private readonly PropertyInfo _nameP;
        private readonly Func<PropertyInfo, Func<Yueluo, object>> _switcher;
        private readonly Dictionary<PropertyInfo, Func<Yueluo, object>> _dic;

        public FuncSearchTest()
        {
            _yueluo = Yueluo.Create();
            var propertyInfos = typeof(Yueluo).GetProperties().ToArray();

            CreateCacheArrayD(propertyInfos);

            _switcher = ValueGetter.CreateGetter<Yueluo, object>(propertyInfos,
                info => Expression.SwitchCase(Expression.Constant(CreateFunc(info)), Expression.Constant(info)));
            _dic = propertyInfos.ToDictionary(x => x, CreateFunc);

            _nameP = typeof(Yueluo).GetProperty(nameof(Yueluo.Name));
            _func = x => x.Name;
        }

        private void CreateCacheArrayD(IReadOnlyCollection<PropertyInfo> propertyInfos)
        {
            _target = new Func<Yueluo, object>[propertyInfos.Count];
            foreach (var info in propertyInfos)
            {
                var key = GetKey(info);
                var index = key % propertyInfos.Count;
                _target[index] = CreateFunc(info);
            }
        }

        private static Func<Yueluo, object> CreateFunc(PropertyInfo info)
        {
            var pExp = Expression.Parameter(typeof(Yueluo), "x");
            var bodyExp = Expression.Property(pExp, info);
            var finalExp =
                Expression.Lambda<Func<Yueluo, object>>(Expression.Convert(bodyExp, typeof(object)), pExp);
            return finalExp.Compile();
        }

        private static int GetKey(MemberInfo info)
        {
            var token = info.MetadataToken;
            return token;
        }

        [Benchmark(Baseline = true)]
        public string Directly() => _func(_yueluo);

        [Benchmark]
        public string ArrayIndex() => (string) _target[_nameP.MetadataToken % _target.Length](_yueluo);

        [Benchmark]
        public string SwitchExp() => (string) _switcher(_nameP)(_yueluo);

        [Benchmark]
        public string Dic() => (string) _dic[_nameP](_yueluo);
    }
}

The benchmark

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19041.572 (2004/?/20H1)
Intel Xeon CPU E5-2678 v3 2.50GHz, 1 CPU, 24 logical and 12 physical cores
.NET Core SDK=5.0.100-rc.2.20479.15
  [Host]       : .NET Core 2.1.23 (CoreCLR 4.6.29321.03, CoreFX 4.6.29321.01), X64 RyuJIT
  net461       : .NET Framework 4.8 (4.8.4250.0), X64 RyuJIT
  net48        : .NET Framework 4.8 (4.8.4250.0), X64 RyuJIT
  netcoreapp21 : .NET Core 2.1.23 (CoreCLR 4.6.29321.03, CoreFX 4.6.29321.01), X64 RyuJIT
  netcoreapp31 : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
  netcoreapp5  : .NET Core 5.0.0 (CoreCLR 5.0.20.47505, CoreFX 5.0.20.47505), X64 RyuJIT

Conclusion

  1. A dictionary is a real drag .
  2. Framework Really pulling the hip .
  3. Net 5 It's just too strong .
  4. Array skipping is the fastest of the indirect schemes .

Chart

FuncSearch

data

Method Job Runtime Mean Error StdDev Ratio RatioSD Rank
Directly net461 .NET 4.6.1 0.9347 ns 0.0363 ns 0.0321 ns 1.00 0.00 1
ArrayIndex net461 .NET 4.6.1 15.0904 ns 0.3820 ns 0.3752 ns 16.13 0.64 2
SwitchExp net461 .NET 4.6.1 17.1585 ns 0.0624 ns 0.0521 ns 18.30 0.56 3
Dic net461 .NET 4.6.1 34.3348 ns 0.2447 ns 0.2169 ns 36.77 1.18 4
                 
Directly net48 .NET 4.8 0.6338 ns 0.0233 ns 0.0218 ns 1.00 0.00 1
ArrayIndex net48 .NET 4.8 15.3098 ns 0.2794 ns 0.2613 ns 24.17 0.69 2
SwitchExp net48 .NET 4.8 17.8113 ns 0.0740 ns 0.0656 ns 28.20 0.98 3
Dic net48 .NET 4.8 33.7930 ns 0.4538 ns 0.4245 ns 53.36 1.64 4
                 
Directly netcoreapp21 .NET Core 2.1 1.2153 ns 0.1168 ns 0.1434 ns 1.00 0.00 1
ArrayIndex netcoreapp21 .NET Core 2.1 4.6545 ns 0.1044 ns 0.0871 ns 4.01 0.51 2
SwitchExp netcoreapp21 .NET Core 2.1 8.1995 ns 0.2567 ns 0.2747 ns 6.81 0.90 3
Dic netcoreapp21 .NET Core 2.1 24.2669 ns 0.5440 ns 0.5586 ns 20.07 2.51 4
                 
Directly netcoreapp31 .NET Core 3.1 0.7382 ns 0.1148 ns 0.1074 ns 1.00 0.00 1
ArrayIndex netcoreapp31 .NET Core 3.1 4.3580 ns 0.1299 ns 0.1085 ns 6.10 0.77 2
SwitchExp netcoreapp31 .NET Core 3.1 7.5985 ns 0.1310 ns 0.1161 ns 10.45 1.41 3
Dic netcoreapp31 .NET Core 3.1 22.2433 ns 0.2756 ns 0.2443 ns 30.61 4.20 4
                 
Directly netcoreapp5 .NET Core 5.0 1.3323 ns 0.0527 ns 0.0493 ns 1.00 0.00 1
ArrayIndex netcoreapp5 .NET Core 5.0 5.0058 ns 0.1361 ns 0.1206 ns 3.77 0.15 2
SwitchExp netcoreapp5 .NET Core 5.0 9.0576 ns 0.0985 ns 0.0921 ns 6.81 0.26 3
Dic netcoreapp5 .NET Core 5.0 20.4052 ns 0.2724 ns 0.2275 ns 15.44 0.59 4

summary

Whether it's array skipping or expression Switch All solutions can solve this problem , And it's faster than using a dictionary .

But there is a problem , At present, the author has not found anything about MetadataToken Whether you really have the same as class The nature of continuity .

Therefore, it is recommended to use Switch Scheme realization .

I'm just a knowledge Porter

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GitHub Project address :https://github.com/newbe36524/Newbe.ObjectVisitor

Gitee Project address :https://gitee.com/yks/Newbe.ObjectVisitor

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