apewer-dotnet/Apewer/Surface/FileMapping.cs

#if NET40 || NET461

using Apewer.Internals.Interop;
using System;
using System.Collections.Generic;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;

namespace Apewer.Surface
{

    /// <summary></summary>
    internal class FileMapping
    {

        /// <summary>创建内存映射。</summary>
        /// <param name="argPath">文件路径。</param>
        /// <param name="argHandle">内存映射句柄。</param>
        /// <param name="argBlock">块大小。</param>
        /// <returns>映射成功。</returns>
        internal bool Create(string argPath, ref IntPtr argHandle, ref UInt32 argBlock)
        {
            var DesiredAccess = Constant.GENERIC_READ | Constant.GENERIC_WRITE;
            var ShareMode = FileShare.ReadWrite;
            var CreationDesposition = FileMode.OpenOrCreate;
            var FlagsAndAttributes = Constant.FILE_ATTRIBUTE_NORMAL | Constant.FILE_FLAG_SEQUENTIAL_SCAN;

            if (File.Exists(argPath))
            {
                try
                {
                    var fh = Kernel32.CreateFile(argPath, DesiredAccess, ShareMode, IntPtr.Zero, CreationDesposition, FlagsAndAttributes, IntPtr.Zero);
                    if (Constant.INVALID_HANDLE_VALUE != (int)fh)
                    {
                        // 创建内存句柄。
                        var mh = Kernel32.CreateFileMapping(fh, IntPtr.Zero, Constant.PAGE_READWRITE, 0, 0, Guid.NewGuid().ToString());

                        // 获取系统信息。
                        var si = new SystemInfo();
                        Kernel32.GetSystemInfo(ref si);

                        // 得到系统页分配粒度。
                        uint vag = si.dwAllocationGranularity;
                        uint vflh = 0;

                        // 获取文件长度。
                        uint vfl = Kernel32.GetFileSize(fh, out vflh);
                        vfl |= (((uint)vflh) << 32);

                        // 关闭文件句柄 。
                        Kernel32.CloseHandle(fh);
                        uint vbl = 1000 * vag;
                        if (vfl < 1000 * vag) vbl = vfl;

                        // 返回。
                        argHandle = mh;
                        argBlock = vbl;
                        return true;
                    }
                }
                catch { }
            }
            argHandle = IntPtr.Zero;
            argBlock = 0;
            return false;
        }

        /// <summary>从内存映射中读取数据。</summary>
        /// <param name="argHandle">内存映射句柄。</param>
        /// <param name="argBlock">块大小。</param>
        /// <param name="argOffset">读取的位置。</param>
        /// <param name="argLength">读取的长度。</param>
        /// <returns>读取的结果。</returns>
        internal byte[] Read(IntPtr argHandle, UInt32 argBlock, Int32 argOffset, Int32 argLength)
        {
            var DesiredAccess = (uint)(Constant.FILE_MAP_COPY | Constant.FILE_MAP_READ | Constant.FILE_MAP_WRITE);

            if ((argHandle != IntPtr.Zero) && (argBlock > 0) && (argOffset > 0) && (argLength > 0))
            {
                try
                {
                    // 映射视图，得到地址 。
                    var mapaddress = Kernel32.MapViewOfFile(argHandle, DesiredAccess, (uint)(argOffset >> 32), (uint)(argOffset & 0xFFFFFFFF), argBlock);
                    if (mapaddress != IntPtr.Zero)
                    {
                        // 从非托管的内存中复制内容到托管的内存中。
                        var start = argOffset;
                        var length = argLength;
                        var buffer = new byte[argBlock];
                        Marshal.Copy(mapaddress, buffer, start, length);
                        return buffer;
                    }
                }
                catch { }
            }
            return new byte[0];
        }

        /// <summary>关闭内存映射。</summary>
        /// <param name="argHandle">内存映射句柄。</param>
        internal static void Close(IntPtr argHandle)
        {
            if (argHandle == IntPtr.Zero) return;
            try { Kernel32.CloseHandle(argHandle); } catch { }
        }

    }

}

#endif