config.pl

package SomeObject;

sub open {
  my $self = shift;
  $self->on(connect => \&connect);
  $self->trigger_open; # low-level start conneection
}

sub connect {
  my $self = shift;
  my $delay = Mojo::IOLoop->delay(
    sub {
      my $delay = shift;
      $self->config_a($delay->begin);
      $self->config_b($delay->begin);
    },
    sub {
      $self->attach_normal_listeners;
    },
  );
}

# likewise for config_b
sub config_a {
  my ($self, $cb) = @_;
  my $delay = Mojo::IOLoop->delay(
    sub {
      my $delay = shift;
      $self->ua->get($config_a1, $delay->begin)
    },
    sub {
      my $delay = shift;
      $self->ua->get($config_a2, $delay->begin)
    },
    sub {
      $self->$cb();
    }
  )
}

sub attach_normal_listeners {
  my $self = shift;
  $self->on(event1 => sub { ... });
  $self->on(event2 => sub { ... });
  ...
}