(* Step 6: the OCaml GC beside Flan's arenas.
   Allocate hard, then compact -- the most disruptive thing the collector does,
   since compaction is what actually moves blocks. C checks its arena after. *)

external note : nativeint -> unit = "spike_note_arena"

let () =
  Callback.register "spike_churn" (fun (rounds : int) ->
      let keep = ref [] in
      for i = 1 to rounds do
        (* Garbage, plus a little that survives, so the heap really grows. *)
        for _ = 1 to 2000 do ignore (Bytes.create 512) done;
        if i mod 10 = 0 then keep := Bytes.create 4096 :: !keep
      done;
      Gc.full_major ();
      Gc.compact ();
      let s = Gc.quick_stat () in
      Printf.sprintf
        "allocated %.0f words, %d major collections, %d compactions, heap %d words"
        s.Gc.minor_words s.Gc.major_collections s.Gc.compactions s.Gc.heap_words);
  ignore note