use AE             qw( );
use AnyEvent::HTTP qw( http_get );
use Coro           qw( async );
use Coro::Channel  qw( );

sub make_request {
   my ($url, $cb) = @_;
   
   http_get($url,
      ...,
      sub {
         ...
         $cb->();
      },
   );
}

my $num_workers = 10;

my $q = Coro::Channel->new();

my @threads;
for (1..$num_workers) {
   push @threads, async {
      while (my $url = $q->get()) {
         my $cv = AE::cv();
         make_request($url, $cv);
         $cv->recv();
      }
   }
}

while (my $url = get_next_url()) {
   $q->put($url);
}

$q->shutdown();
$_->join() for @threads;