Have you read Net::Ping? It describes how you can ping multiple hosts without even needing threads. Please just read Net::Ping and ask specific questions after you've done so. The relevant example from the Net::Ping documentation is:

# Like tcp protocol, but with many hosts
    $p = Net::Ping->new("syn");
    $p->port_number(getservbyname("http", "tcp"));
    foreach $host (@host_array) {
      $p->ping($host);
    }
    while (($host,$rtt,$ip) = $p->ack) {
      print "HOST: $host [$ip] ACKed in $rtt seconds.\n";
    }
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Thanks Corion