For delays of finer granularity than one second, you may use Perl's syscall() interface to access setitimer(2) if your system supports it, or else see select(). It is usually a mistake to intermix alarm() and sleep() calls.

If you want to use alarm() to time out a system call you need to use an eval/die pair. You can't rely on the alarm causing the system call to fail with $! set to EINTR because Perl sets up signal handlers to restart system calls on some systems. Using eval/die always works.

    eval {
        local $SIG{ALRM} = sub { die "alarm\n" };       # NB \n required
        alarm $timeout;
        $nread = sysread SOCKET, $buffer, $size;
        alarm 0;
    };
    die if $@ && $@ ne "alarm\n";       # propagate errors
    if ($@) {
        # timed out
    }
    else {
        # didn't
    }