Attempt at parallelizing OCaml computation

test.ml

open Core.Std
open Async.Std
open Async_parallel.Std

let workers = ["localhost"; "localhost"]

let worker h =
  Pipe.iter_without_pushback (Hub.listen_simple h) ~f:(fun (id, `Ping) ->
      printf "%s Got Ping\n%!" (Hub.Client_id.sexp_of_t id |> Sexp.to_string_hum);
      Hub.send h id `Pong)
  >>| fun () -> `Done
  
let main () =
  printf "Start\n%!";
  Deferred.List.iter [1; 2; 3; 4] ~f:(fun i ->
      Parallel.spawn ~where:Parallel.round_robin worker
      >>= fun (c, res) ->
      printf "Value = %d\n%!" i;
      let rec loop = function
        | 0 -> Channel.close c
        | i ->
        Channel.write c `Ping;
        Channel.read c
        >>= fun `Pong ->
        Clock.after (sec 1.)
        >>= fun _ -> loop (i - 1)
      in
      loop 2
    )
  >>> fun _ -> Shutdown.shutdown 0

let _ =
  Parallel.init ~cluster:{ Cluster.master_machine = Unix.gethostname ();
                           worker_machines = workers } ();
  main ();
  never_returns (Scheduler.go ())