* Re: [Caml-list] Difference between ocamlc and ocamlopt when marshalling reference
2010-06-02 12:16 Difference between ocamlc and ocamlopt when marshalling reference Mathias Kende
@ 2010-06-02 16:40 ` Fabrice Le Fessant
0 siblings, 0 replies; 2+ messages in thread
From: Fabrice Le Fessant @ 2010-06-02 16:40 UTC (permalink / raw)
To: Mathias Kende; +Cc: caml-list
Hi,
The main difference is that "p" is a closure in bytecode, but just a
pointer in native code: in bytecode, "p" references "r", and so a
closure is needed; in native code, the reference to "r" in "p" is a
direct access to the module structure, and so "p" does not need to keep
a reference to "r". So, when you marshal "p" in bytecode, you follow the
closure and the reference, that are stored in "s", and they are
duplicated when "s" is unmarshalled.
I think Marshal.Closures is only expected for hacking anyway, so you
should not really assume anything on its behavior ;-)
--Fabrice
Mathias Kende wrote, On 06/02/2010 02:16 PM:
> Hi,
>
> I found a difference on the way global references used inside a function
> are handled with respect to marshalling between ocamlc and ocamlopt.
>
> See the exemple below :
>
> -------------- a.ml ---------------
> let r = ref 0
> let p () = Printf.printf "%d\n" !r
> let s = Marshal.to_string p [Marshal.Closures]
> let () = r := 1
> let q : unit -> unit = Marshal.from_string s 0
> let () = q ()
> -----------------------------------
> $ ocamlc a.ml
> $ ./a.out
> 0
> $ ocamlopt a.ml
> $ ./a.out
> 1
> -----------------------------------
>
> I am not sure which semantic is the "good" one. They are both
> interesting, but having only one is definitely simpler.
>
> Is this a known problem ? is there fundamental reasons in the compilers
> for which it can not be changed ?
>
> Cheers,
>
> Mathias
>
> _______________________________________________
> Caml-list mailing list. Subscription management:
> http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
> Archives: http://caml.inria.fr
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>
--
Fabrice LE FESSANT
Chercheur, Equipe ASAP
(As Scalable As Possible)
http://www.lefessant.net/
INRIA-Futurs, Bat P - 112
Parc Orsay Université
2-4, rue Jacques Monod
F-91893 Orsay Cedex, FRANCE
^ permalink raw reply [flat|nested] 2+ messages in thread