C#中的高性能内存操作的利器:Span<T>和Memory<T>

int[] numbers = { 1, 2, 3, 4, 5 };
Span<int> span = numbers; 
span[0] = 10; 
Console.WriteLine(numbers[0]);

using System;

class Program
{
    static void Main()
    {
        string orderData = "ORD-12345-AB: 已发货";

        // 传统方式 - 创建新的字符串对象
        string orderId1 = orderData.Substring(0, 11); // 分配新内存
        string status1 = orderData.Substring(13);     // 再次分配新内存

        // 使用Span<T> - 不创建新的字符串对象
        ReadOnlySpan<char> dataSpan = orderData.AsSpan();
        ReadOnlySpan<char> orderId2 = dataSpan.Slice(0, 11); // 不分配新内存
        ReadOnlySpan<char> status2 = dataSpan.Slice(13);     // 不分配新内存

        // 必要时才将Span转换为string
        Console.WriteLine($"订单号: {orderId2.ToString()}");
        Console.WriteLine($"状态: {status2.ToString()}");
    }
}

using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace AppSpanMemory
{
    internal class Program
    {
        static unsafe void Main()
        {
            Span<int> stackNums = stackalloc int[100];

            for (int i = 0; i < stackNums.Length; i++)
            {
                stackNums[i] = i * 10;
            }

            // 获取Span起始位置的指针
            void* ptr = Unsafe.AsPointer(ref MemoryMarshal.GetReference(stackNums));

            Console.WriteLine($"Span内存地址: 0x{(ulong)ptr:X}");

            // 打印前10个元素
            var firstTen = stackNums.Slice(0, 10);
            foreach (var n in firstTen)
            {
                Console.Write($"{n} ");
            }
            Console.ReadKey();
        }
    }
}

// Memory<T>的基本使用
Memory<int> memory = new int[] { 1, 2, 3, 4, 5 };
Span<int> spanFromMemory = memory.Span; // 从Memory获取Span视图
spanFromMemory[0] = 20;
Console.WriteLine(memory.Span[0]);

using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace AppSpanMemory
{
    internal class Program
    {
        static async Task Main()
        {
            // 创建一个4KB的缓冲区
            byte[] buffer = new byte[4096];
            Memory<byte> memoryBuffer = buffer; 

            using FileStream fileStream = new FileStream("bigdata.dat", FileMode.Open, FileAccess.Read);
            int bytesRead = await fileStream.ReadAsync(memoryBuffer);

            if (bytesRead > 0)
            {
                Memory<byte> actualData = memoryBuffer.Slice(0, bytesRead);
                ProcessData(actualData.Span);
            }

            Console.WriteLine($"读取了 {bytesRead} 字节的数据");
        }

        static void ProcessData(Span<byte> data)
        {
            Console.WriteLine($"前10个字节: {BitConverter.ToString(data.Slice(0, Math.Min(10, data.Length)).ToArray())}");
        }
    }
}

using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace AppSpanMemory
{
    internal class Program
    {
        static async Task Main()
        {
            string csvLine = "张三,30,北京市海淀区,软件工程师";
            ParseCsvLine(csvLine.AsSpan());
        }

        public static void ParseCsvLine(ReadOnlySpan<char> line)
        {
            int start = 0;
            int fieldIndex = 0;

            for (int i = 0; i < line.Length; i++)
            {
                if (line[i] == ',')
                {
                    // 不创建新字符串
                    ReadOnlySpan<char> field = line.Slice(start, i - start);
                    ProcessField(fieldIndex, field);

                    start = i + 1;
                    fieldIndex++;
                }
            }

            // 处理最后一个字段
            if (start < line.Length)
            {
                ReadOnlySpan<char> lastField = line.Slice(start);
                ProcessField(fieldIndex, lastField);
            }
        }

        private static void ProcessField(int index, ReadOnlySpan<char> field)
        {
            Console.WriteLine($"字段 {index}: '{field.ToString()}'");
        }

    }
}

using System;
using System.Buffers.Binary;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;

namespace AppSpanMemory
{
    internal class Program
    {
        static async Task Main()
        {
            string csvLine = "张三,30,北京市海淀区,软件工程师";

            byte[] payloadBytes = Encoding.UTF8.GetBytes(csvLine);

            // 头部4字节 + 数据长度4字节 + 数据体
            byte[] fileData = new byte[4 + 4 + payloadBytes.Length];

            // 写入头部标识 "DATA"
            fileData[0] = (byte)'D';
            fileData[1] = (byte)'A';
            fileData[2] = (byte)'T';
            fileData[3] = (byte)'A';

            // 写入数据长度（小端）
            BinaryPrimitives.WriteInt32LittleEndian(fileData.AsSpan(4, 4), payloadBytes.Length);

            // 写入数据体
            payloadBytes.CopyTo(fileData.AsSpan(8));

            // 传入文件字节数据的只读切片
            ProcessBinaryFile(fileData);
        }

        public static void ProcessBinaryFile(ReadOnlySpan<byte> data)
        {
            // [4字节头部标识][4字节数据长度][实际数据]
            if (data.Length < 8)
            {
                thrownew ArgumentException("数据格式不正确");
            }

            // 检查头部标识"DATA"
            ReadOnlySpan<byte> header = data.Slice(0, 4);
            if (!(header[0] == 'D' && header[1] == 'A' && header[2] == 'T' && header[3] == 'A'))
            {
                thrownew ArgumentException("无效的文件头");
            }

            // 读取数据长度 (小端字节序)
            int dataLength = BinaryPrimitives.ReadInt32LittleEndian(data.Slice(4, 4));

            // 确保数据完整
            if (data.Length < 8 + dataLength)
            {
                thrownew ArgumentException("数据不完整");
            }

            // 获取实际数据部分
            ReadOnlySpan<byte> payload = data.Slice(8, dataLength);

            Console.WriteLine($"有效载荷大小: {payload.Length} 字节");
            Console.WriteLine($"前10个字节: {BitConverter.ToString(payload.Slice(0, Math.Min(10, payload.Length)).ToArray())}");
        }

    }
}