NativeBuffering,一种高性能、零内存分配的序列化解决方案[性能测试续篇]

在《NativeBuffering,一种高性能、零内存分配的序列化解决方案[性能测试篇]》我比较了NativeBuffering和System.Text.Json两种序列化方式的性能,通过性能测试结果可以看出NativeBuffering具有非常明显的优势,有的方面的性能优势甚至是“碾压式”的,唯独针对字符串的序列化性能不够理想。我趁这个周末对此做了优化,解决了这块短板,接下来我们就来看看最新的性能测试结果和背后“加速”的原理。[NativeBuffering@github]

一、新版的性能测试结果

我使用《NativeBuffering,一种高性能、零内存分配的序列化解决方案[性能测试篇]》提供的测试用例,选用的依然是如下这个Person类型,它的绝大部分数据成员都是字符串。

[BufferedMessageSource]
public partial class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string[] Hobbies { get; set; }
    public string Address { get; set; }
    public string PhoneNumber { get; set; }
    public string Email { get; set; }
    public string Gender { get; set; }
    public string Nationality { get; set; }
    public string Occupation { get; set; }
    public string EducationLevel { get; set; }
    public string MaritalStatus { get; set; }
    public string SpouseName { get; set; }
    public int NumberOfChildren { get; set; }
    public string[] ChildrenNames { get; set; }
    public string[] LanguagesSpoken { get; set; }
    public bool HasPets { get; set; }
    public string[] PetNames { get; set; }

    public static Person Instance = new Person
    {
        Name = "Bill",
        Age = 30,
        Hobbies = new string[] { "Reading", "Writing", "Coding" },
        Address = "123 Main St.",
        PhoneNumber = "555-555-5555",
        Email = "bill@gmail.com",
        Gender = "M",
        Nationality = "China",
        Occupation = "Software Engineer",
        EducationLevel = "Bachelor's",
        MaritalStatus = "Married",
        SpouseName = "Jane",
        NumberOfChildren = 2,
        ChildrenNames = new string[] { "John", "Jill" },
        LanguagesSpoken = new string[] { "English", "Chinese" },
        HasPets = true,
        PetNames = new string[] { "Fido", "Spot" }
    };
}

这是采用的测试案例。Benchmark方法SerializeAsJson直接将静态字段Instance表示的Person对象序列化成JSON字符串,采用NativeBuffering的Benchmark方法SerializeAsNativeBuffering直接调用WriteTo扩展方法(通过Source Generator生成)对齐进行序列化,并利用一个ArraySegment<T>结构返回序列化结果。WriteTo方法具有一个类型为Func<int, byte[]>的参数,我们使用它来提供一个存放序列化结果的字节数组。作为Func<int, byte[]>输入参数的整数代表序列化结果的字节长度,这样我们才能确保提供的字节数组具有充足的存储空间。

[MemoryDiagnoser]
public class Benchmark
{
    private  static readonly Func<int, byte[]> _bufferFactory = ArrayPool<byte>.Shared.Rent;

    [Benchmark]
    public string SerializeAsJson() => JsonSerializer.Serialize(Person.Instance);

    [Benchmark]
    public void SerializeNativeBuffering()
    {
        var arraySegment = Person.Instance.WriteTo(_bufferFactory);
        ArrayPool<byte>.Shared.Return(arraySegment.Array!);
    }
}

这是上一个版本的测试结果,虽然NativeBuffering具有“零内存分配”的巨大优势,但是在耗时上会多一些。造成这个劣势的主要原因来源于针对字符串的编码,因为NativeBuffering在序列化过程需要涉及两次编码,一次是为了计算总的字节数,另一次才是生成序列化结果。

image

如果切换到目前最新版本(0.1.5),可以看出NativeBuffering的性能已经得到了极大的改善,并且明显优于JSON序列化的性能(对于JSON序列化,两次测试具体的耗时之所以具有加大的差异,是因为测试机器配置不同,12代和13代i7的差异)。而在内存分配层面,针对NativeBuffering的序列化依然是“零分配”。

image

二、背后的故事

接下来我们就来简单说明一下为什么NativeBuffering针对字符串的序列化明显优于JSON序列化,这要从BufferedString这个自定义的结构说起。如下所示的就是Source Generator为Person类型生成的BufferedMessage类型,可以看出它的原有的字符串类型的成员在此类型中全部转换成了BufferedString类型的只读属性。

public unsafe readonly struct PersonBufferedMessage : IReadOnlyBufferedObject<PersonBufferedMessage>
{
    public static PersonBufferedMessage DefaultValue => throw new NotImplementedException();
    public NativeBuffer Buffer { get; }
    public PersonBufferedMessage(NativeBuffer buffer) => Buffer = buffer;
    public static PersonBufferedMessage Parse(NativeBuffer buffer) => new PersonBufferedMessage(buffer);
    public BufferedString Name => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(0);
    public System.Int32 Age => Buffer.ReadUnmanagedField<System.Int32>(1);
    public ReadOnlyNonNullableBufferedObjectList<BufferedString> Hobbies => Buffer.ReadNonNullableBufferedObjectCollectionField<BufferedString>(2);
    public BufferedString Address => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(3);
    public BufferedString PhoneNumber => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(4);
    public BufferedString Email => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(5);
    public BufferedString Gender => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(6);
    public BufferedString Nationality => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(7);
    public BufferedString Occupation => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(8);
    public BufferedString EducationLevel => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(9);
    public BufferedString MaritalStatus => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(10);
    public BufferedString SpouseName => Buffer.ReadNonNullableBufferedObjectField<BufferedString>(11);
    public System.Int32 NumberOfChildren => Buffer.ReadUnmanagedField<System.Int32>(12);
    public ReadOnlyNonNullableBufferedObjectList<BufferedString> ChildrenNames => Buffer.ReadNonNullableBufferedObjectCollectionField<BufferedString>(13);
    public ReadOnlyNonNullableBufferedObjectList<BufferedString> LanguagesSpoken => Buffer.ReadNonNullableBufferedObjectCollectionField<BufferedString>(14);
    public System.Boolean HasPets => Buffer.ReadUnmanagedField<System.Boolean>(15);
    public ReadOnlyNonNullableBufferedObjectList<BufferedString> PetNames => Buffer.ReadNonNullableBufferedObjectCollectionField<BufferedString>(16);
}

BufferedString在NativeBuffering中用来表示字符串。如代码片段所示,BufferedString 同样实现了IReadOnlyBufferedObject<BufferedString>接口,以为着它也是对一段字节序列的封装。BufferedString提供了针对字符串类型的隐式转换,所以我们在编程的时候可以将它当成普通字符串来使用。

public unsafe readonly struct BufferedString : IReadOnlyBufferedObject<BufferedString>
{
    public static BufferedString DefaultValue { get; }
    static BufferedString()
    {
        var size = CalculateStringSize(string.Empty);
        var bytes = new byte[size];

        var context = BufferedObjectWriteContext.Create(bytes);
        context.WriteString(string.Empty);
        DefaultValue = new BufferedString(new NativeBuffer(bytes));
    }
    public BufferedString(NativeBuffer buffer) => _start = buffer.Start;
    public BufferedString(void* start) => _start = start;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static BufferedString Parse(NativeBuffer buffer) =>  new(buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static BufferedString Parse(void* start) => new(start);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int CalculateSize(void* start) => Unsafe.Read<int>(start);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public string AsString()
    {
        string v = default!;
        Unsafe.Write(Unsafe.AsPointer(ref v), new IntPtr(Unsafe.Add<byte>(_start, IntPtr.Size * 2)));
        return v;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static implicit operator string(BufferedString value) => value.AsString();

    public override string ToString() => AsString();

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int CalculateStringSize(string? value)
    {
        var byteCount = value is null ? 0 : Encoding.Unicode.GetByteCount(value);
        var size = _headerByteCount + byteCount;
        return Math.Max(IntPtr.Size * 3 + sizeof(int), size);
    }

    private static readonly int _headerByteCount = sizeof(nint) + sizeof(nint) + sizeof(nint) + sizeof(int);
}

值得一提的是,BufferedString向String的类型转换是没有任何开销的,这一切源自它封装的这段字节序列的结构。我曾经在《你知道.NET的字符串在内存中是如何存储的吗?》中介绍过字符串对象自身在内存中的布局,而BufferedString封装的字节序列就是在这段内容加上前置的4/8个字节(x84为4字节,x64需要添加4字节Padding确保内存对齐)来表示总的字节数。当BufferedString转换成String类型时,只需要将返回的字符串变量指向TypeHandle部分的地址就可以了,这一点体现在上述的AsString方法上。

image

也正是因为NativeBuffering在序列化字符串的时候,生成的字节序列与字符串对象的内存布局一致,所以不在需要对字符串进行编码,直接按照如下所示的方式进行内存拷贝就可以了。这正是NativeBuffering针对字符串的序列化的性能得以提升的原因,不过整个序列化过程中还是需要计算字符串针对默认编码(Unicode)的字节长度。

image

posted @ 2023-11-06 08:29  Artech  阅读(1158)  评论(1编辑  收藏  举报