Segmentation fault when assigning function to reference in different thread about ocaml-multicore HOT 2 CLOSED

effect Yield : unit

let () =
  let kk = ref (fun () -> failwith "continuation") in
  let assig_k = ref true in
  begin match
    print_endline "0";
    perform Yield;
    print_endline "1";
    Unix.sleep 1;
    perform Yield;
    print_endline "2"
  with
    | () -> print_endline "done"
    | effect Yield k ->
        print_endline "before kk assig";
        if !assig_k then begin
          assig_k := false;
          print_endline "assigning k";
          kk := (fun () -> continue k ())
        end else begin
          print_endline "not assigning k";
          kk := (fun () -> ())
        end;
        print_endline "after kk assig"
  end;
  print_endline "before spawn";
  Domain.spawn (fun () -> !kk ());
  print_endline "after spawn";
  Unix.sleep 20;
  print_endline "after sleep"