use forks; 
use Thread::Queue qw( );   # 3.01+

use constant NUM_WORKERS => 10;

sub work {
    my ($client) = @_;
    print("$client start...\n");
    sleep(3 + int(rand(2)));
    print("$client done.\n");
}

{
   my $q = Thread::Queue->new();
   for (1..NUM_WORKERS) {
      async {
         while (my $client = $q->dequeue()) {
            work($client);
         }
      };
   }

   $q->enqueue($_) for 1..33;
   $q->end();
   $_->join() for forks->list();
}