/// <summary>
/// 从内存文件映射中,分段创建一个读写的流
/// </summary>
/// <param name="offset">读写的起始偏移</param>
/// <param name="count">总映射的数量,建议映射的数量少于1G</param>
/// <returns>返回一个读写流</returns>
public MemoryMappingFileStream CreateMappingStream(long offset, long count)
{
var readCount = Math.Min(count, fileLength - offset);
var realOffsetValue = offset - offset % systemAllocMin; //计算出所需的真实起始偏移
var baseOffset = 0L;
if (offset < systemAllocMin)
{
baseOffset = offset;
readCount += offset;
}
uint dwFileOffsetLow = (uint)(realOffsetValue & 0xffffffffL);
uint dwFileOffsetHigh = (uint)(realOffsetValue >> 0x20);
IntPtr lpbMapAddress = UnManageAPI.MapViewOfFile(targetMappingFileHandle, UnManageAPI.FILE_MAP_COPY | UnManageAPI.FILE_MAP_READ | UnManageAPI.FILE_MAP_WRITE,
dwFileOffsetHigh, dwFileOffsetLow,
(uint)readCount);
if (lpbMapAddress == IntPtr.Zero)
{
throw new IOException("无法映射指定的偏移");
}
return(new MemoryMappingFileStream(lpbMapAddress, baseOffset, readCount - baseOffset));
}
private void OpenFile(string fileName)
{
if (!File.Exists(fileName))
{
throw new FileNotFoundException();
}
IntPtr fileHandle = UnManageAPI.CreateFile(fileName, UnManageAPI.GENERIC_READ | UnManageAPI.GENERIC_WRITE, FileShare.Read | FileShare.Write, IntPtr.Zero, FileMode.Open, UnManageAPI.FILE_ATTRIBUTE_NORMAL | UnManageAPI.FILE_FLAG_SEQUENTIAL_SCAN, IntPtr.Zero);
if (UnManageAPI.INVALID_HANDLE_VALUE == (int)fileHandle)
{
throw new FileLoadException("文件打开出错");
}
uint fileSizeHigh = 0;
//读取文件大小
long fileSize = UnManageAPI.GetFileSize(fileHandle, out fileSizeHigh);
IntPtr mappingFileHandle = UnManageAPI.CreateFileMapping(fileHandle, IntPtr.Zero, UnManageAPI.PAGE_READWRITE, 0, 0, "KugarMapping");
if (mappingFileHandle == IntPtr.Zero)
{
throw new FileLoadException("文件映射出错");
}
fileSize |= (((uint)fileSizeHigh) << 32);
UnManageAPI.CloseHandle(fileHandle);
targetMappingFileHandle = mappingFileHandle;
fileLength = fileSize;
}
protected override void Dispose(bool disposing)
{
base.Dispose(disposing);
if (disposing)
{
UnManageAPI.UnmapViewOfFile(_mappingAddress);
}
}
public override void Flush()
{
var tempMappingLength = Interlocked.Read(ref _mappingLength);
Interlocked.Add(ref tempMappingLength, _baseOffset);
UnManageAPI.FlushViewOfFile(_mappingAddress, (int)tempMappingLength);
//return false;
}
public MemoryMappingFile(string fileName)
{
var sysInf = new UnManageAPI.SYSTEM_INFO();
UnManageAPI.GetSystemInfo(ref sysInf);
if (systemAllocMin == 0L)
{
systemAllocMin = sysInf.dwAllocationGranularity;
}
OpenFile(fileName);
}
protected void Disposed(bool disposing)
{
if (_isDispose)
{
return;
}
if (disposing)
{
UnManageAPI.CloseHandle(targetMappingFileHandle);
_isDispose = true;
}
}