It depends on the nature of the computations. If you're looping through that file yourself:

my $t = time();
while (<$input_fh>) {
  process_a_line();
  if (time() - $t >= 1) {
    $widget->update();
    $t = time();
  }
}
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If the entire file is being atomically processed, then you'll need to get deeper into parallel programming.