C#操作共享内存的一个帮助类，读写和打开

C#操作共享内存的一个帮助类，读写和打开 

    class ShareMemoryHelper
    {
        [DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
        private static extern IntPtr OpenFileMapping(int dwDesiredAccess, [MarshalAs(UnmanagedType.Bool)] bool bInheritHandle, string lpName);
        [DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
        private static extern IntPtr MapViewOfFile(IntPtr hFileMapping, uint dwDesiredAccess, uint dwFileOffsetHigh, uint dwFileOffsetLow, uint dwNumberOfBytesToMap);
        [DllImport("kernel32", EntryPoint = "GetLastError")]
        public static extern int GetLastError();
        [DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr CreateFileMapping(int hFile, IntPtr lpAttributes, uint flProtect, uint dwMaxSizeHi, uint dwMaxSizeLow, string lpName);
        [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);
 
 
        public IntPtr fileMapping = IntPtr.Zero;
        public IntPtr mapView = IntPtr.Zero;
        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_READWRITE = 0x04;
        const int INVALID_HANDLE_VALUE = -1;
        const int ERROR_ALREADY_EXISTS = 183;
        private bool bValid;
        bool m_bAlreadyExist = false;
        bool m_bInit = false;
        long m_MemSize = 0;
        public ShareMemoryHelper(string name, uint length)
        {
            bValid = GetShareMemoryMap(name, length);
        }
        public ShareMemoryHelper()
        {
        }
 
        ~ShareMemoryHelper()
        {
            Close();
        }
        public bool GetShareMemoryMap(string name, uint length)
        {
            m_MemSize = length;
            fileMapping = OpenFileMapping(PAGE_READWRITE, false, name);
            if (fileMapping == IntPtr.Zero)
            {
                return false;
            }
            mapView = MapViewOfFile(fileMapping, (uint)FILE_MAP_READ, 0, 0, length);
            if (mapView == IntPtr.Zero)
            {
                int a = GetLastError();
                return false;
            }
            m_bInit = true;
            return true;
        }
 
        public int CreateShareMemoryMap(string strName, long lngSize)
        {
            if (lngSize <= 0 || lngSize > 0x00800000) lngSize = 0x00800000;
            m_MemSize = lngSize;
            if (strName.Length > 0)
            {
                fileMapping = CreateFileMapping(INVALID_HANDLE_VALUE, IntPtr.Zero, (uint)PAGE_READWRITE, 0, (uint)lngSize, strName);
                if (fileMapping == IntPtr.Zero)
                {
                    return 2; 
                }
 
                if (GetLastError() == ERROR_ALREADY_EXISTS)
                {
                    m_bAlreadyExist = true;
                }
                else
                {
                    m_bAlreadyExist = false;
                }
                mapView = MapViewOfFile(fileMapping, FILE_MAP_WRITE, 0, 0, (uint)lngSize);
                if (mapView == IntPtr.Zero)
                {
                    m_bInit = false;
                    CloseHandle(fileMapping);
                    return 3; 
                }
                else
                {
                   m_bInit = true;
                    if (m_bAlreadyExist == false)
                    {
                    }
                }
            }
            else
            {
                return 1;
            }
            return 0;
        }
 
        public int Write(byte[] bytData, int lngAddr, int lngSize)
        {
            if (lngAddr + lngSize > m_MemSize) return 2;
            if (m_bInit)
            {
                Marshal.Copy(bytData, lngAddr, mapView, lngSize);
            }
            else
            {
                return 1;
            }
            return 0;
        }
 
        public int Read(ref byte[] bytData, int lngAddr, int lngSize)
        {
            if (lngAddr + lngSize > m_MemSize) return 2;
            if (m_bInit)
            {
                Marshal.Copy(mapView, bytData, lngAddr, lngSize);
            }
            else
            {
                return 1;
            }
            return 0;
        }
 
        public void Close()
        {
            if (m_bInit)
            {
                UnmapViewOfFile(mapView);
                CloseHandle(fileMapping);
            }
        }
    }