Just to prove OCaml's gc can collect self referencing record.

output.txt

## Test array size=1048576
(filled - start).live_words = 6291460
(end - filled).live_words = -6291452
(end - start).live_words = 8
(filled - start).live_blocks = 2097153
(end - filled).live_blocks = -2097151
(end - start).live_blocks = 2

selfref_gc_test.ml

(* -*- coding: utf-8 -*- *)

open Core.Std

type 'a t = {value: 'a; mutable prev: 'a t; mutable next: 'a t}

let init value =
  let rec x = {value; prev = x; next = x} in
  x

type stat_log_t =
  {sl_live_words: int; sl_live_blocks: int; sl_msg: string}

let gc_stat msg =
  let open Gc.Stat in
  Gc.full_major ();
  let {live_words; live_blocks; _} = Gc.stat () in
  {sl_msg = msg; sl_live_words = live_words; sl_live_blocks = live_blocks}

let () =
  let default_nobjs = 1024*1024
  in
  let nobjs =
    if (Array.length Sys.argv) <= 1 then
      default_nobjs
    else
      int_of_string Sys.argv.(0)
  in
  Printf.printf "## Test array size=%d\n" nobjs;
  let holder = Array.init nobjs ~f:(fun _ -> None)
  in
  let at_start =
    gc_stat "# Just after the array is initialized with None:"
  in
  for i = 0 to nobjs - 1 do
    holder.(i) <- Some (init i)
  done;
  let at_filled =
    gc_stat "# After the array is filled with selfref records:"
  in
  for i = 0 to nobjs - 1 do
    holder.(i) <- None
  done;
  let at_end =
    gc_stat "# After the array is cleared with None:"
  in
  Printf.printf "(filled - start).live_words = %d\n"
    (at_filled.sl_live_words - at_start.sl_live_words);
  Printf.printf "(end - filled).live_words = %d\n"
    (at_end.sl_live_words - at_filled.sl_live_words);
  Printf.printf "(end - start).live_words = %d\n"
    (at_end.sl_live_words - at_start.sl_live_words);
  Printf.printf "(filled - start).live_blocks = %d\n"
    (at_filled.sl_live_blocks - at_start.sl_live_blocks);
  Printf.printf "(end - filled).live_blocks = %d\n"
    (at_end.sl_live_blocks - at_filled.sl_live_blocks);
  Printf.printf "(end - start).live_blocks = %d\n"
    (at_end.sl_live_blocks - at_start.sl_live_blocks);