my $l = Future::Limiter->from_yaml(<<'YAML');
      request:
          # Make no more than 1 request per second
          # have no more than 4 requests in flight at a time
          # If there is a backlog, process them as quickly as possible
          - burst : 3
          rate : 60/60
          - maximum: 4
      namelookup:
          - burst : 3
          rate : 60/60
  YAML

  ...

my ($host_token, $rate_token);
$limiter->limit( 'request', $hostname, $url )->then(sub {
    my ($host_token, $url ) = @_;
    request_url( $url )->on_ready( undef $host_token );
})->then(sub {
    ...
    undef $host_token;
    undef $rate_token;
});

my( $host_token ) = await $concurrency->limit( $hostname );
my( $rate_token ) = await $rate->limit( $hostname );
request_url( $url )
...

my ($token,@args) = await $limiter->limit('fetch',$url->hostname);
... do work
undef $token; # release token

$limiter->limit('fetch',$url->hostname,$url)->then(sub( $token, $url) {
    return http_request($url)->on_ready(sub { undef $token });
};