Marshal.to_string and mutable values

["Frédéric Gava" <gava@univ-paris12.fr>]

Hi all,

A personnal parallel application crash (but works before) and I am
very surprised to find that the pb is in Marshal.to_string. Take for
example:

let a = ref 0;;

(* no pb *)
Marshal.to_string a [Marshal.Closures];;
-: string = "..."

(* minor pb *)
Marshal.to_string (fun _ -> a) [Marshal.Closures];;
Exception: Invalid_argument "output_value: abstract value (outside heap)"
????
I do not use an abstract value here. But ok, there is peraps side effects
after the serialization of the function.

(* less minor pb *)
let f () =
 let b = ref 0 in b:=!b+1; 1 ;;

Marshal.to_string f [Marshal.Closures];;
Exception: Invalid_argument "output_value: abstract value (outside heap)"
????
I can save this function (with its closure). The reference is completely
local. For my purpose, a processor could not send to another processor a
function wich used some imperative features (for best complexity). That is
so bad...

Those examples comes from "Development of applications with OCaml" by
Chailloux and al. And they suppose to works... and in latest versions of
ocaml, they worked.

Anybody have an idea ? I suppose it is not a bug but I do not know why it is
a pb.

Frédéric Gava