sub _listening {
    my $ok = 0;
    my $s = IO::Socket::INET->new(
        Timeout  => TIMEOUT,
        PeerHost => $_[0],
        Proto    => $_[1],
        PeerPort => $_[2]
    );
    if( $s ) {
        close $s;
        $ok = 1;
    }
    return $ok;
}