EOF on a watched handle

Hello,

the following code is the main part of an example prepared for the workshop, emulating "tail -f":

- snip --

# install "tail -f"
Event->io(
          fd=>\*IN,
          cb=>sub {
                   # check for real news
                   return if eof(IN);

                   # read new line and report it
                   print "New line detected: ", scalar(<IN>), "\n";
                  }
         );

- snip ---

Please note the lines

- snip ---

 # check for real news
 return if eof(IN);

- snip ---

which I had to add because an event occurs even if nothing new arrives in the file. Well, this was ok for me in a demonstration focussed on an io watcher, but now someone asked me if there is a way to avoid callback invokation for EOF. Running the script again, I recognized that it enforces a very high load.

Ok, I suppose this is because of the underlaying select() call. I read the manpage of IO::Select which mentions EOF as an ERROR (to be detected by has_error()), not a "ready to be read" event (checked by can_read()). Nevertheless, even with IO::Select and usage of can_read() EOF is detected as an event as well:

- snip --

use IO::Select;

$s=IO::Select->new;

open(IN, "tailtest.tmp");
$s->add(\*IN);

while ($s->can_read(0))
 {
  next if $s->has_error(0);
  print "New line detected: ", scalar(<IN>), "\n";
 }

- snip --

This surely is a basic problem. The question is if there is a solution? What I'm looking for is to get a read event (poll=>'r') ONLY if there is something to read, not in case of EOF (which could be matched by poll=>'e'). Ideally, this solution would result in a lower load than the example above.

                        Jochen