weakHashtbl.ml

(*
    Copyright © 2011 MLstate

    This file is part of OPA.

    OPA is free software: you can redistribute it and/or modify it under the
    terms of the GNU Affero General Public License, version 3, as published by
    the Free Software Foundation.

    OPA is distributed in the hope that it will be useful, but WITHOUT ANY
    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
    FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for
    more details.

    You should have received a copy of the GNU Affero General Public License
    along with OPA. If not, see <http://www.gnu.org/licenses/>.
*)
(* http://remi.vanicat.free.fr/ocaml/hweak/ *)
(* Perhaps we can replace this module by (modified?) above hweak
   implementation... ? *)

module type WeakedType = sig
  type t
  val compare : t -> t -> int
  val hash : t -> int
end

module Make (HK : Hashtbl.HashedType)(HD : WeakedType) = struct
  module WS = Weak.Make
    (struct
       include HD
       let equal a b = HD.compare a b = 0
     end)

  module HT = Hashtbl.Make(HK)

  type key = HK.t

  module S = Set.Make(HD)

  type t = {
    htbl : HD.t HT.t;
    wset : WS.t;
    mutable strong : S.t;
  }

  let create i = {
    htbl = HT.create i;
    wset = WS.create i;
    strong = S.empty;
  }

  let remove t k =
    try
      let v = HT.find t.htbl k in
      WS.remove t.wset v;
      HT.remove t.htbl k;
      t.strong <- S.remove v t.strong
    with Not_found -> ()

  let add t k v =
    let vcopy = Obj.obj (Obj.dup (Obj.repr v)) in
    HT.add t.htbl k vcopy;
    WS.add t.wset v;
    Gc.finalise (fun _ -> HT.remove t.htbl (k:HK.t)) v

  let mem t k = (HT.mem t.htbl k)

  let find t k = WS.find t.wset (HT.find t.htbl k)

  let strong t k v =
    if not (mem t k) then add t k v;
    t.strong <- S.add v t.strong

  let relax t k =
    t.strong <- S.remove (find t k) t.strong

  let size t =
    HT.length t.htbl

end