code: protected synchronized void invalidateSharedReader() throws IOException
     {
        // also close the read-only reader
        if (readOnlyReader != null)
        {
           readOnlyReader.release();
           readOnlyReader = null;
        }
        // invalidate shared reader
        if (sharedReader != null)
        {
           sharedReader.release();
           sharedReader = null;
        }
     }
docs: Closes the shared reader.
  
  @throws IOException if an error occurs while closing the reader.