threadn {
    eval {
        sighandler = {};
        alarm 15;        ## alarm#1
        start threadn+1;
        start threadn+2;
        threadn+2->join
        threadn+1->join
    }
    alarm 0;
}
threadn+1{
    eval{
        sighandler = {};
        alarm 15;          ## alarm#2
        @input = qx[ ping ];
    }
    alarm 0;
}
threadn+2 {
    @input = qx[ tcpdump;
    return @input;
}