Thanks for your reply, ikegami.

The code I posted is really an "overview" of what appears in several modules, and in fact we are checking for errors as you described:

if (not defined $bytes) {
  warn . . .
  $sel->remove($handle);
  next;
}
[download]

At this point I'd love to get an error or warning, but unfortunately it simply returns 0 bytes as if the handle were empty.