C#

. . .
. . .  this code is in a function.. for simplicity I reported a snippet
public enum 	dbLockType	{ _none =0, _lock, _unLock, _default}
long lockPos = -1;
long lockRec = -1;
int  blockSize = 100;
 
  FileStream DtFile = new FileStream(@"\\server\d\folder\test.txt", FileMode.Open, FileAccess.ReadWrite,
 FileShare.ReadWrite,8000); 
. . .
. . .

public bool getBufferFromDisk(long RecordNumber, byte[] toArray, int startingAt, int length, dbLockType dbLock)
{
  long seekPosition = GetFilePos(RecordNumber); // calc RecordNumber*blockSize
  try {
	DtFile .Seek(seekPosition, System.IO.SeekOrigin.Begin);
	DtFile .Read(toArray, startingAt, length);
	if ( dbLock == dbLockType._lock) {
  	   if ( lockPos > -1)
		DtFile .Unlock(lockPos, blockSize);  // unlock previous locks
	   DtFile .Lock(seekPosition, blockSize); 
	   
	   lockPos = seekPosition;
	   lockRec = RecordNumber;
	}
  }
  catch(IOException e) {
	return false;	
  }
  return true;
}

public int SetSite(object site)
        {
            SHDocVw.IWebBrowser2 m_pIWebBrowser2 = site as SHDocVw.IWebBrowser2;
            IServiceProvider ISP = site as IServiceProvider;

            if (m_pIWebBrowser2 != null)
            {
                Marshal.ReleaseComObject(m_pIWebBrowser2);
                m_pIWebBrowser2 = null;
            }

            if (Explorer != null)
            {
                Marshal.ReleaseComObject(Explorer);
                Explorer = null;
            }

            if (ISP != null)
            {
                Guid IID_IUnknown = new
                Guid("{00000000-0000-0000-C000-000000000046}");
                Guid IID_IWebBrowserApp = new
                Guid("{0002DF05-0000-0000-C000-00000000046}");
                object pOut;

                try
                {
                    ISP.QueryService(ref IID_IWebBrowserApp, ref IID_IUnknown, out
                    pOut);
                    Explorer = (WebBrowserClass)Marshal.CreateWrapperOfType(pOut as
                    IWebBrowser2, typeof(WebBrowserClass));
                }
                catch (Exception e)
                {
                    System.Windows.Forms.MessageBox.Show(e.Message, "Talkative Browser");
                }
            }

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct OLECMDTEXT
    {
        public uint cmdtextf;
        public uint cwActual;
        public uint cwBuf;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 100)]
        public char rgwz;
    }


    [StructLayout(LayoutKind.Sequential)]
    public struct OLECMD
    {
        public uint cmdID;
        public uint cmdf;
    }


    [ComImport,
    Guid("b722bccb-4e68-101b-a2bc-00aa00404770"),
    InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IOleCommandTarget
    {
        void QueryStatus(ref Guid pguidCmdGroup, UInt32 cCmds,
        [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] OLECMD[] prgCmds, ref 
        OLECMDTEXT CmdText);
        void Exec(ref Guid pguidCmdGroup, uint nCmdId, uint nCmdExecOpt, ref object
        pvaIn, ref object pvaOut);
    }