如何动态扩展内存映射文件

| 我已经使用C＃解决了以下要求。 -创建一个可以快速接收大量数据的应用程序 -您必须能够在收到更多数据时分析接收到的数据。 -使用尽可能少的CPU和磁盘我对算法的想法是

SIZE = 10MB
Create a mmf with the size of SIZE
On data recived:
  if data can\'t fit mmf: increase mmf.size by SIZE
  write the data to mmf

->使用先前的“房间/空间”时，光盘上的大小增加10MB。如何在C＃中完成“按大小增加mmf.size”？我已经找到了许多有关创建mmfs和视图的简单示例，但是我看到的唯一的地方（链接）会大幅增加mmfs区域的代码使用了无法编译的代码。任何帮助将不胜感激。编辑这将导致异常：

private void IncreaseFileSize()
{
    int theNewMax = this.currentMax + INCREMENT_SIZE;
    this.currentMax = theNewMax;

    this.mmf.Dispose();

    this.mmf = MemoryMappedFile.CreateFromFile(this.FileName, FileMode.Create, \"MyMMF\", theNewMax);
    this.view = mmf.CreateViewAccessor(0, theNewMax);            
}

引发此异常：该进程无法访问文件\'C：\\ Users \\ moberg \\ Documents \\ data.bin \'，因为该文件正在被另一个进程使用。

已邀请:

5 个回复

抢垢洛韧

一旦将文件映射到内存中，就无法增加其大小。这是内存映射文件的已知限制。 ...您必须计算或估计完成文件的大小，因为文件映射对象的大小是静态的；一旦创建，它们的大小就不能增加或减小。一种策略是使用存储在给定大小（例如1GB或2GB）的非持久性内存映射文件中的块。您可以通过自己设计的顶层ViewAccessor管理这些（可能从MemoryMappedViewAccessor进行所需方法的基本传递）。编辑：或者您可以只创建一个您希望使用的最大大小的非持久性内存映射文件（例如，启动8GB，并在应用程序启动时使用参数对其进行调整），并在每个逻辑上检索MemoryMappedViewAccessor块。在请求每个视图之前，非持久文件将不使用物理资源。

桔马牛

好吧，你可以！这是我对可增长的内存映射文件的实现：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.IO.MemoryMappedFiles;

namespace MmbpTree
{
    public unsafe sealed class GrowableMemoryMappedFile : IDisposable
    {

        private const int AllocationGranularity = 64 * 1024;

        private class MemoryMappedArea
        {
            public MemoryMappedFile Mmf;
            public byte* Address;
            public long Size;
        }


        private FileStream fs;

        private List<MemoryMappedArea> areas = new List<MemoryMappedArea>();
        private long[] offsets;
        private byte*[] addresses;

        public long Length
        {
            get {
                CheckDisposed();
                return fs.Length;
            }
        }

        public GrowableMemoryMappedFile(string filePath, long initialFileSize)
        {
            if (initialFileSize <= 0 || initialFileSize % AllocationGranularity != 0)
            {
                throw new ArgumentException(\"The initial file size must be a multiple of 64Kb and grater than zero\");
            }
            bool existingFile = File.Exists(filePath);
            fs = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
            if (existingFile)
            {
                if (fs.Length <=  0 || fs.Length % AllocationGranularity != 0)
                {
                    throw new ArgumentException(\"Invalid file. Its lenght must be a multiple of 64Kb and greater than zero\");
                }
            }
            else
            { 
                fs.SetLength(initialFileSize);
            }
            CreateFirstArea();
        }

        private void CreateFirstArea()
        {
            var mmf = MemoryMappedFile.CreateFromFile(fs, null, fs.Length, MemoryMappedFileAccess.ReadWrite,  null, HandleInheritability.None, true);
            var address = Win32FileMapping.MapViewOfFileEx(mmf.SafeMemoryMappedFileHandle.DangerousGetHandle(), 
                Win32FileMapping.FileMapAccess.Read | Win32FileMapping.FileMapAccess.Write,
                0, 0, new UIntPtr((ulong) fs.Length), null);
            if (address == null) throw new Win32Exception();

            var area = new MemoryMappedArea
            {
                Address = address,
                Mmf = mmf,
                Size = fs.Length
            };
            areas.Add(area);

            addresses = new byte*[] { address };
            offsets = new long[] { 0 };

        }


        public void Grow(long bytesToGrow)
        {
            CheckDisposed();
            if (bytesToGrow <= 0 || bytesToGrow % AllocationGranularity != 0)  {
                throw new ArgumentException(\"The growth must be a multiple of 64Kb and greater than zero\");
            }
            long offset = fs.Length;
            fs.SetLength(fs.Length + bytesToGrow);
            var mmf = MemoryMappedFile.CreateFromFile(fs, null, fs.Length, MemoryMappedFileAccess.ReadWrite, null, HandleInheritability.None, true);
            uint* offsetPointer = (uint*)&offset;
            var lastArea = areas[areas.Count - 1];
            byte* desiredAddress = lastArea.Address + lastArea.Size;
            var address = Win32FileMapping.MapViewOfFileEx(mmf.SafeMemoryMappedFileHandle.DangerousGetHandle(), 
                Win32FileMapping.FileMapAccess.Read | Win32FileMapping.FileMapAccess.Write,
                offsetPointer[1], offsetPointer[0], new UIntPtr((ulong)bytesToGrow), desiredAddress);
            if (address == null) {
                address = Win32FileMapping.MapViewOfFileEx(mmf.SafeMemoryMappedFileHandle.DangerousGetHandle(),
                   Win32FileMapping.FileMapAccess.Read | Win32FileMapping.FileMapAccess.Write,
                   offsetPointer[1], offsetPointer[0], new UIntPtr((ulong)bytesToGrow), null);
            }
            if (address == null) throw new Win32Exception();
            var area = new MemoryMappedArea {
                Address = address,
                Mmf = mmf,
                Size = bytesToGrow
            };
            areas.Add(area);
            if (desiredAddress != address) {
                offsets = offsets.Add(offset);
                addresses = addresses.Add(address);
            }
        }

        public byte* GetPointer(long offset)
        {
            CheckDisposed();
            int i = offsets.Length;
            if (i <= 128) // linear search is more efficient for small arrays. Experiments show 140 as the cutpoint on x64 and 100 on x86.
            {
                while (--i > 0 && offsets[i] > offset);
            }
            else // binary search is more efficient for large arrays
            {
                i = Array.BinarySearch<long>(offsets, offset);
                if (i < 0) i = ~i - 1;
            }
            return addresses[i] + offset - offsets[i];
        }

        private bool isDisposed;

        public void Dispose()
        {
            if (isDisposed) return;
            isDisposed = true;
            foreach (var a in this.areas)
            {
                Win32FileMapping.UnmapViewOfFile(a.Address);
                a.Mmf.Dispose();
            }
            fs.Dispose();
            areas.Clear();
        }

        private void CheckDisposed()
        {
            if (isDisposed) throw new ObjectDisposedException(this.GetType().Name);
        }

        public void Flush()
        {
            CheckDisposed();
            foreach (var area in areas)
            {
                if (!Win32FileMapping.FlushViewOfFile(area.Address, new IntPtr(area.Size))) {
                    throw new Win32Exception();
                }
            }
            fs.Flush(true);
        }
    }
}

这是the6ѭ类：

using System;
using System.Runtime.InteropServices;

namespace MmbpTree
{
    public static unsafe class Win32FileMapping
    {
        [Flags]
        public enum FileMapAccess : uint
        {
            Copy = 0x01,
            Write = 0x02,
            Read = 0x04,
            AllAccess = 0x08,
            Execute = 0x20,
        }

        [DllImport(\"kernel32.dll\", SetLastError = true)]
        public static extern byte* MapViewOfFileEx(IntPtr mappingHandle,
                                            FileMapAccess access,
                                            uint offsetHigh,
                                            uint offsetLow,
                                            UIntPtr bytesToMap,
                                            byte* desiredAddress);

        [DllImport(\"kernel32.dll\", SetLastError = true)]
        public static extern bool UnmapViewOfFile(byte* address);


        [DllImport(\"kernel32.dll\", SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool FlushViewOfFile(byte* address, IntPtr bytesToFlush);
    }
}

这是you8ѭ类：

using System;

namespace MmbpTree
{
    public static class Extensions
    {
        public static T[] Add<T>(this T[] array, T element)
        {
            var result = new T[array.Length + 1];
            Array.Copy(array, result, array.Length);
            result[array.Length] = element;
            return result;
        }

        public static unsafe byte*[] Add(this byte*[] array, byte* element)
        {
            var result = new byte*[array.Length + 1];
            Array.Copy(array, result, array.Length);
            result[array.Length] = element;
            return result;
        }
    }
}

如您所见，我采用了不安全的方法。这是获得内存映射文件性能优势的唯一方法。为此，您需要考虑以下概念：块或页面。这是您使用连续内存地址和存储空间的最小区域。块或页面的大小必须是基础系统页面大小（4Kb）的倍数。初始文件大小。它必须是块或页面大小的倍数，并且必须是系统分配粒度（64Kb）的倍数。文件增长。它必须是块或页面大小的倍数，并且必须是系统分配粒度（64Kb）的倍数。例如，您可能要使用1Mb的页面大小，64Mb的文件增长和1Gb的初始大小。您可以通过调用GetPointer获得指向页面的指针，使用Grow扩展文件并使用Flush刷新文件：

const int InitialSize = 1024 * 1024 * 1024;
const int FileGrowth = 64 * 1024 * 1024;
const int PageSize = 1024 * 1024;
using (var gmmf = new GrowableMemoryMappedFile(\"mmf.bin\", InitialSize))
{
    var pageNumber = 32;
    var pointer = gmmf.GetPointer(pageNumber * PageSize);

    // you can read the page content:
    byte firstPageByte = pointer[0];
    byte lastPageByte = pointer[PageSize - 1];

    // or write it
    pointer[0] = 3;
    pointer[PageSize -1] = 43;


    /* allocate more pages when needed */
    gmmf.Grow(FileGrowth);

    /* use new allocated pages */

    /* flushing the file writes to the underlying file */ 
    gmmf.Flush();

}

倾坞髓

代码不编译的原因是因为它使用了不存在的重载。要么自己创建一个文件流，然后将其传递给正确的重载（假设2000是您的新大小）：

FileStream fs = new FileStream(\"C:\\MyFile.dat\", FileMode.Open);
MemoryMappedFile mmf = MemoryMappedFile.CreateFromFile(fs, \"someName\", 2000,
 MemoryMappedFileAccess.ReadWriteExecute, null, HandleInheritablity.None, false);

或使用此重载来跳过filstream的创建：

MemoryMappedFile mmf = MemoryMappedFile.CreateFromFile(\"C:\\MyFile.dat\", 
          FileMode.Open, \"someName\", 2000);

济畦刨

使用带有capacity参数的MemoryMappedFile.CreateFromFile重载。

掀辟髓观粟

我发现关闭并重新创建具有相同名称但新大小的mmf可以满足所有意图和目的

                using (var mmf = MemoryMappedFile.CreateOrOpen(SenderMapName, 1))
                {
                    mmf.SafeMemoryMappedFileHandle.Close();
                }
                using (var sender = MemoryMappedFile.CreateNew(SenderMapName, bytes.Length))

而且真的很快。

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如何动态扩展内存映射文件

5 个回复

发起人

.net_4.0

memory_mapped_files

c#

问题状态

如何动态扩展内存映射文件

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5 个回复

发起人

.net_4.0

memory_mapped_files

c#

问题状态