...
my $dump_thread = threads->new(\&tcp_dump, $macaddress, $dns_name);
sleep 1;
my $ping_thread = threads->new(\&ping, $dns_name);
...
$ping_thread->join();
...
// this section checks if tcpdump captured a packet and does something with it 
...
my $dump_pid = `pidof tcpdump`;
`kill $dump_pid`;
$dump_thread->join();
...