Re: [Caml-list] Will the data allocated by caml_alloc be automatically freed by g arbage collector?

[Romain Bardou <bardou@lri.fr>]

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Le 01/01/2012 17:01, syshen a ¨¦crit :
>
> Dear All:
>
> I am writing a program that include a main loop written in Ocaml and a
> sub-module written in C. The main loop called the sub-module a lot, and
> a huge array is returned from each call.
>
> So I use the standard C-Caml interface to return these huge data as
> shown below:
>
> extern "C" value minisat_save_proof(value unit) {
> CAMLparam0();
> CAMLlocal1( ml_data );
> vec<long>& vi=(solver->proof)->save("minisat_save_proof");
> int sz=vi.size();
> ml_data = caml_alloc (sz,0);
> for (int i=0;i<sz;i++) {
> Store_field( ml_data, i, Val_int((int)(vi[i])) );
> }
> CAMLreturn( ml_data );
> }
>
> In the main ocaml program loop, there is a call to a ocaml method A,
> which again call this C method minisat_save_proof.
>
> When ocaml method A got these data returned from minisat_save_proof, it
> call another method B to clear all data structure in the sub-module
> written in C, and then exit to the main loop and call Gc.compress to
> collect all garbage.
> So in this case I think the memory usage of my program should be the
> same like before calling minisat_save_proof , because the returned data
> should be collected by the garbage collector when exiting the method A
> to the main loop.
>
> But from the unix "top" command, I find that these huge return data
> seems to remain in memory and consume all my memory step by step.
>
> So I want to know if there is any method to free these data?

Hello,

As far as I know, yes, caml_alloc() allocates its data in the OCaml heap 
and your big value will thus be garbage collected.

Maybe you could check that your value is indeed garbage collected by using:
   Gc.finalise (fun _ -> print_endline "I am being garbage collected") v
where v is the value returned by minisat_save_proof.

If the value is not garbage collected, then maybe you forgot that you 
put the value in some table or something.

Cheers,