my @threads;
for my $i (0..19) {
  print "THREAD SPAWNED.\n";
  $threads[$i] = threads->new(\&mainsub, $i);
  $threads[$i]->detach;
  sleep 1;
}

##</code><code>##

print "THREAD SPAWNED.\n";
$thr1 = threads->new(\&mainsub,0);
$thr1->detach;
sleep 1;

print "THREAD SPAWNED.\n";
$thr2 = threads->new(\&mainsub,1);
$thr2->detach;
sleep 1;

# ...