pingecho() or a ping object with the tcp protocol use alarm() to
implement the timeout.  So, don't use alarm() in your program while
you are using pingecho() or a ping object with the tcp protocol.  The
udp and icmp protocols do not use alarm() to implement the timeout.

##</code><code>##

$p = Net::Ping->new();
$p->ping(\@list_of_hosts, $timeout, $num_forks);