$\=$/;
use IO::Socket::INET;


my @hosts = qw(pantagruel gargantua foo bar quux);

my (%active,%sockets);

my $maxconn = 30; # or as much as your OS permits ;-)
my $timeout = 20;

sub setup_sock {
    my $fh = eval {
        IO::Socket::INET->new(
           PeerAddr => "$_[0]:23",
           Blocking => 0,
        )
    };
    unless ($fh) {
        print "$_[0] not reachable";
        return;
    }   
    $active{$_[0]} = $fh;
    $sockets{fileno($fh)} = $_[0];
    # print "$_[0] fileno ",fileno($fh);
}

sub close_sock {
    my $fileno = shift;
    my $host   = $sockets{$fileno};
    $active{$host}->close;
    delete $active{$host};
    delete $sockets{$fileno};
}

sub set_bits {
    my $rin;
    for (keys %active) {
        vec($rin, fileno($active{$_}),1) = 1;
    }   
    $rin;
}   

while (@hosts || keys %active) {
    # $c++; print "pass $c";
    setup_sock(shift @hosts) while ($maxconn > keys %active and @hosts);
    my $rin = set_bits;
    my $rout; 
    select($rout=$rin,undef,undef,$timeout);

    # if there has been a timeout, there has been no response,
    # and $rout has no bit set. mark those hosts as unreachable

    if ($rout eq "\0") {
        for(0..unpack"B*",$rin) {
            if (vec $rin,$_,1) {
                print "no answer from $sockets{$_} (fileno $_)";
                close_sock($_);
            }
        }
    }

    for(0..unpack"B*",$rout) {
        if (vec $rout,$_,1) {
            print "$sockets{$_} ($_) is alive";
            close_sock($_);
        }   
    }   
}