interface ihello
{
  in void hello();
  out void world();

  behaviour
  {
    on hello: world;
  }
}

component async_blocking
{
  provides ihello h;

  behaviour
  {
    requires dzn.async i;

    blocking on h.hello(): i.req();
    on i.ack(): {h.world(); h.reply();}
  }
}