file upload process

[El Capitan]

Another (most likely) trivial question for the experts.
When a large file is uploaded from an html form page, it appears the file is
loaded BEFORE I can start some kind of "graphical metering" response:

sub handler() {
        my $apr = Apache::Request->new($r);

        my $upload = $apr->upload;
      my $fh = $upload->fh;
      my $lines = 0;
      while(<$fh>) {
        ++$lines;
            ... do some return html trick stuff
      }
        ...
}

Before the loop through the file handle, the uploaded file has already been
loaded (I think).  Is there some way to capture the download stream (when
its actually downloading) and begin a display process back to the customer?

Thanks in advance,
Kirk