System.IO.FileStream.VerifyOSHandlePosition C# (CSharp) Method

        private void VerifyOSHandlePosition()
        {
            bool verifyPosition = _exposedHandle; // in release, only verify if we've given out the handle such that someone else could be manipulating it
#if DEBUG
            verifyPosition = true; // in debug, always make sure our position matches what the OS says it should be
#endif
            if (verifyPosition && CanSeek)
            {
                long oldPos = _filePosition; // SeekCore will override the current _position, so save it now
                long curPos = SeekCore(0, SeekOrigin.Current);
                if (oldPos != curPos)
                {
                    // For reads, this is non-fatal but we still could have returned corrupted 
                    // data in some cases, so discard the internal buffer. For writes, 
                    // this is a problem; discard the buffer and error out.
                    _readPos = _readLength = 0;
                    if (_writePos > 0)
                    {
                        _writePos = 0;
                        throw new IOException(SR.IO_FileStreamHandlePosition);
                    }
                }
            }
        }