sub gps {
    my $gps_device;
    while (1) {
        goto END if $die == 1;
        if ($gps_start == 1) {
            $gps_device = GPS::NMEA->new(Port => $gps, Baud => 4800) o
+r die;
            my $timeout = 5;
            while (1){
                #stops the warnings in the GPS device module
                local $^W = 0;
                print "before\n";
                eval {
                    local $SIG{ALRM} = sub {die "GPS Device has timed 
+out\n"};
                    alarm $timeout;
                    ($ns,$lat,$ew,$lon) = $gps_device->get_position;
                    #warn $@ if $@;
                    alarm 0;
                };
                die if $@ && $@ ne "GPS Device has timed out\n";
                if ($@){
                    print "WARNING\n";
                }
                else{
                    print "nope\n";
                }
                
                #($ns,$lat,$ew,$lon) = $gps_device->get_position;
                print "after\n";
                print "$die\n";
                goto END if $die == 1;
                last if $gps_start == 0;
                sleep 3;
            }
            undef $gps_device;
        } else {sleep 4}
    }
    END:
}
[download]

You could try setting the environment var set PERL_SIGNALS=unsafe prior to running your script and see if that will allow alarm to interupt the underlying IO call. I think this has to be set prior to perl being run, but I wouldn't swear to it.

See Safe signals for (a little) explanation of what this does.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

From my recollection, alarm won't work correctly in a thread on linux, the parent thread gets all the alarms. So you might be able to collect the SIG{ALRM} in the parent thread, and then send the signal to the thread. Or you may be able to find another workaround, like a separate timer thread, which times the gps sub.

Another workaround I've seen, is to eval a fork-&-exec in the thread, and you can get the alarm to work in the child pid. If I recall correctly...... :-)

Personnally I would use a separate timer thread, and use shared variables to somehow communicate and handle the timeout.

---

I'm not really a human, but I play one on earth. Cogito ergo sum a bum