use Thread::Pool;
$pool = Thread::Pool->new(
  {
   do => sub {shift; print "do(@_)\n"; return $result; },
   workers => 20,
  },
);

# then you submit your jobs
foreach(keys %jobs) {
    $ids{$_} = $pool->job(...arguments to do...);
}
while(keys %ids) {
    foreach(keys %ids) {
        if(@result = $pool->result_dontwait($_)) {
            $results{$_} = [@result];
            delete($ids{$_});
        }
    }
}