用C#实现的内存映射

当文件过大时，无法一次性载入内存时，就需要分次，分段的载入文件

主要是用了以下的WinAPI

 

LPVOID MapViewOfFile(HANDLE hFileMappingObject,

　　DWORD dwDesiredAccess,

　　DWORD dwFileOffsetHigh,

　　DWORD dwFileOffsetLow,

　　DWORD dwNumberOfBytesToMap);

 

　　MapViewOfFile() 函数负责把文件数据映射到进程的地址空间，参数hFileMappingObject 为 CreateFileMapping()返回的文件映像对象句柄。参数dwDesiredAccess则再次指定了对文件数据的访问方式，而且同样要与 CreateFileMapping()函数所设置的保护属性相匹配。虽然这里一再对保护属性进行重复设置看似多余，但却可以使应用程序能更多的对数据的保护属性实行有效控制。MapViewOfFile()函数允许全部或部分映射文件，在映射时，需要指定数据文件的偏移地址以及待映射的长度。其中，文件的偏移地址由DWORD型的参数dwFileOffsetHigh和dwFileOffsetLow组成的64位值来指定，而且必须是操作系统的分配粒度的整数倍，对于Windows操作系统，分配粒度固定为64KB。当然，也可以通过如下代码来动态获取当前操作系统的分配粒度：

　　SYSTEM_INFO sinf;

　　GetSystemInfo(&sinf);

　　DWORD dwAllocationGranularity = sinf.dwAllocationGranularity;

　　参数dwNumberOfBytesToMap指定了数据文件的映射长度，这里需要特别指出的是，对于Windows 9x操作系统，如果MapViewOfFile()无法找到足够大的区域来存放整个文件映射对象，将返回空值(NULL);但是在Windows 2000下，MapViewOfFile()只需要为必要的视图找到足够大的一个区域即可，而无须考虑整个文件映射对象的大小。

由此看出，分页映射文件时，每页的起始位置startpos,必须为64K的整数倍。

 

以下贴出源代码，防止忘记了

 

using System;using System.Collections.Generic;using System.Text;using System.Runtime.InteropServices;namespace BlueVision.SaYuan.FileMapping{public class ShareMemory{[DllImport( "user32.dll", CharSet = CharSet.Auto )]public static extern IntPtr SendMessage( IntPtr hWnd, int Msg, int wParam, IntPtr lParam );[DllImport( "Kernel32.dll", CharSet = CharSet.Auto )]public static extern IntPtr CreateFileMapping( IntPtr hFile, IntPtr lpAttributes, uint flProtect, uint dwMaxSizeHi, uint dwMaxSizeLow, string lpName );[DllImport( "Kernel32.dll", CharSet = CharSet.Auto )]public static extern IntPtr OpenFileMapping( int dwDesiredAccess, [MarshalAs( UnmanagedType.Bool )] bool bInheritHandle, string lpName );[DllImport( "Kernel32.dll", CharSet = CharSet.Auto )]public static extern IntPtr MapViewOfFile( IntPtr hFileMapping, uint dwDesiredAccess, uint dwFileOffsetHigh, uint dwFileOffsetLow, uint dwNumberOfBytesToMap );[DllImport( "Kernel32.dll", CharSet = CharSet.Auto )]public static extern bool UnmapViewOfFile( IntPtr pvBaseAddress );[DllImport( "Kernel32.dll", CharSet = CharSet.Auto )]public static extern bool CloseHandle( IntPtr handle );[DllImport( "kernel32", EntryPoint = "GetLastError" )]public static extern int GetLastError();[DllImport( "kernel32.dll" )]static extern void GetSystemInfo( out SYSTEM_INFO lpSystemInfo );[StructLayout( LayoutKind.Sequential )]public struct SYSTEM_INFO{public ushort processorArchitecture;ushort reserved;public uint pageSize;public IntPtr minimumApplicationAddress;public IntPtr maximumApplicationAddress;public IntPtr activeProcessorMask;public uint numberOfProcessors;public uint processorType;public uint allocationGranularity;public ushort processorLevel;public ushort processorRevision;}/// <summary>/// 获取系统的分配粒度/// </summary>/// <returns></returns>public static uint GetPartitionsize(){SYSTEM_INFO sysInfo;GetSystemInfo( out sysInfo );return sysInfo.allocationGranularity;}const int ERROR_ALREADY_EXISTS = 183;const int FILE_MAP_COPY = 0x0001;const int FILE_MAP_WRITE = 0x0002;const int FILE_MAP_READ = 0x0004;const int FILE_MAP_ALL_ACCESS = 0x0002 | 0x0004;const int PAGE_READONLY = 0x02;const int PAGE_READWRITE = 0x04;const int PAGE_WRITECOPY = 0x08;const int PAGE_EXECUTE = 0x10;const int PAGE_EXECUTE_READ = 0x20;const int PAGE_EXECUTE_READWRITE = 0x40;const int SEC_COMMIT = 0x8000000;const int SEC_IMAGE = 0x1000000;const int SEC_NOCACHE = 0x10000000;const int SEC_RESERVE = 0x4000000;IntPtr m_fHandle;IntPtr m_hSharedMemoryFile = IntPtr.Zero;IntPtr m_pwData = IntPtr.Zero;bool m_bAlreadyExist = false;bool m_bInit = false;uint m_MemSize = 0x1400000;//20Mlong m_offsetBegin = 0;long m_FileSize = 0;FileReader File = new FileReader();/// <summary>/// 初始化文件/// </summary>/// <param name="MemSize">缓冲大小</param>public ShareMemory( string filename, uint memSize ){// 分页映射文件时，每页的起始位置startpos,必须为64K的整数倍。// memSize即缓存区的大小必须是系统分配粒度的整倍说，window系统的分配粒度是64KBthis.m_MemSize = memSize;Init( filename );}/// <summary>/// 默认映射20M缓冲/// </summary>/// <param name="filename"></param>public ShareMemory( string filename ){this.m_MemSize = 0x1400000;Init( filename );}~ShareMemory(){Close();}/// <summary>/// 初始化共享内存/// /// 共享内存名称/// 共享内存大小/// </summary>/// <param name="strName"></param>protected void Init( string strName ){//if (lngSize <= 0 || lngSize > 0x00800000) lngSize = 0x00800000;if ( !System.IO.File.Exists( strName ) ) throw new Exception( "未找到文件" );System.IO.FileInfo f = new System.IO.FileInfo( strName );m_FileSize = f.Length;m_fHandle = File.Open( strName );if ( strName.Length > 0 ){//创建文件映射m_hSharedMemoryFile = CreateFileMapping( m_fHandle, IntPtr.Zero, ( uint )PAGE_READONLY, 0, ( uint )m_FileSize, "mdata" );if ( m_hSharedMemoryFile == IntPtr.Zero ){m_bAlreadyExist = false;m_bInit = false;throw new Exception( "CreateFileMapping失败LastError=" + GetLastError().ToString() );}elsem_bInit = true;////映射第一块文件//m_pwData = MapViewOfFile(m_hSharedMemoryFile, FILE_MAP_READ, 0, 0, (uint)m_MemSize);//if (m_pwData == IntPtr.Zero)//{// m_bInit = false;// throw new Exception("m_hSharedMemoryFile失败LastError=" + GetLastError().ToString());//}}}/// <summary>/// 获取高32位/// </summary>/// <param name="intValue"></param>/// <returns></returns>private static uint GetHighWord( UInt64 intValue ){return Convert.ToUInt32( intValue >> 32 );}/// <summary>/// 获取低32位/// </summary>/// <param name="intValue"></param>/// <returns></returns>private static uint GetLowWord( UInt64 intValue ){return Convert.ToUInt32( intValue & 0x00000000FFFFFFFF );}/// <summary>/// 获取下一个文件块 块大小为20M/// </summary>/// <returns>false 表示已经是最后一块文件</returns>public uint GetNextblock(){if ( !this.m_bInit ) throw new Exception( "文件未初始化。" );//if ( m_offsetBegin + m_MemSize >= m_FileSize ) return false;uint m_Size = GetMemberSize();if ( m_Size == 0 ) return m_Size;// 更改缓冲区大小m_MemSize = m_Size;//卸载前一个文件//bool l_result = UnmapViewOfFile( m_pwData );//m_pwData = IntPtr.Zero;m_pwData = MapViewOfFile( m_hSharedMemoryFile, FILE_MAP_READ, GetHighWord( ( UInt64 )m_offsetBegin ), GetLowWord( ( UInt64 )m_offsetBegin ), m_Size );if ( m_pwData == IntPtr.Zero ){m_bInit = false;throw new Exception( "映射文件块失败" + GetLastError().ToString() );}m_offsetBegin = m_offsetBegin + m_Size;return m_Size; //创建成功}/// <summary>/// 返回映射区大小/// </summary>/// <returns></returns>private uint GetMemberSize(){if ( m_offsetBegin >= m_FileSize ){return 0;}else if ( m_offsetBegin + m_MemSize >= m_FileSize ){long temp = m_FileSize - m_offsetBegin;return ( uint )temp;}elsereturn m_MemSize;}/// <summary>/// 关闭内存映射/// </summary>public void Close(){if ( m_bInit ){UnmapViewOfFile( m_pwData );CloseHandle( m_hSharedMemoryFile );File.Close();}}/// <summary>/// 从当前块中获取数据/// </summary>/// <param name="bytData">数据</param>/// <param name="lngAddr">起始数据</param>/// <param name="lngSize">数据长度，最大值=缓冲长度</param>/// <param name="Unmap">读取完成是否卸载缓冲区</param>/// <returns></returns>public void Read( ref byte[] bytData, int lngAddr, int lngSize, bool Unmap ){if ( lngAddr + lngSize > m_MemSize )throw new Exception( "Read操作超出数据区" );if ( m_bInit ){// string bb = Marshal.PtrToStringAuto(m_pwData);//Marshal.Copy( m_pwData, bytData, lngAddr, lngSize );}else{throw new Exception( "文件未初始化" );}if ( Unmap ){bool l_result = UnmapViewOfFile( m_pwData );if ( l_result )m_pwData = IntPtr.Zero;}}/// <summary>/// 从当前块中获取数据/// </summary>/// <param name="bytData">数据</param>/// <param name="lngAddr">起始数据</param>/// <param name="lngSize">数据长度，最大值=缓冲长度</param>/// <exception cref="Exception: Read操作超出数据区"></exception>/// <exception cref="Exception: 文件未初始化"></exception>/// <returns></returns>public void Read( ref byte[] bytData, int lngAddr, int lngSize ){if ( lngAddr + lngSize > m_MemSize )throw new Exception( "Read操作超出数据区" );if ( m_bInit ){Marshal.Copy( m_pwData, bytData, lngAddr, lngSize );}else{throw new Exception( "文件未初始化" );}}/// <summary>/// 从当前块中获取数据/// </summary>/// <param name="lngAddr">缓存区偏移量</param>/// <param name="byteData">数据数组</param>/// <param name="StartIndex">数据数组开始复制的下标</param>/// <param name="lngSize">数据长度，最大值=缓冲长度</param>/// <exception cref="Exception: 起始数据超过缓冲区长度"></exception>/// <exception cref="Exception: 文件未初始化"></exception>/// <returns>返回实际读取值</returns>public uint ReadBytes( int lngAddr, ref byte[] byteData, int StartIndex, uint intSize ){if ( lngAddr >= m_MemSize )throw new Exception( "起始数据超过缓冲区长度" );if ( lngAddr + intSize > m_MemSize )intSize = m_MemSize - ( uint )lngAddr;if ( m_bInit ){IntPtr s = new IntPtr( ( long )m_pwData + lngAddr ); // 地址偏移Marshal.Copy( s, byteData, StartIndex, ( int )intSize );}else{throw new Exception( "文件未初始化" );}return intSize;}/// <summary>/// 写数据/// </summary>/// <param name="bytData">数据</param>/// <param name="lngAddr">起始地址</param>/// <param name="lngSize">个数</param>/// <returns></returns>private int Write( byte[] bytData, int lngAddr, int lngSize ){if ( lngAddr + lngSize > m_MemSize ) return 2; //超出数据区if ( m_bInit ){Marshal.Copy( bytData, lngAddr, m_pwData, lngSize );}else{return 1; //共享内存未初始化}return 0; //写成功}}internal class FileReader{const uint GENERIC_READ = 0x80000000;const uint OPEN_EXISTING = 3;System.IntPtr handle;[DllImport( "kernel32", SetLastError = true )]public static extern System.IntPtr CreateFile(string FileName, // file nameuint DesiredAccess, // access modeuint ShareMode, // share modeuint SecurityAttributes, // Security Attributesuint CreationDisposition, // how to createuint FlagsAndAttributes, // file attributesint hTemplateFile // handle to template file);[System.Runtime.InteropServices.DllImport( "kernel32", SetLastError = true )]static extern bool CloseHandle(System.IntPtr hObject // handle to object);public IntPtr Open( string FileName ){// open the existing file for reading handle = CreateFile(FileName,GENERIC_READ,0,0,OPEN_EXISTING,0,0);if ( handle != System.IntPtr.Zero ){return handle;}else{throw new Exception( "打开文件失败" );}}public bool Close(){return CloseHandle( handle );}}}