Thanks for the help on the list. I decided to change Glut.timerFunc for 
the following code, passing the Caml function and its argument using a C 
int (transmitted to the times) which is in fact a pointer to a Caml 
pair. This pointer is registered as a global root and removed by the 
callback itself. I give the code bellow if someone wants to write 
something similar.

A small question: why do people use callback trough a name and a 
hashtable instead of passing the callback inside C variables (global or 
local) ? It could save a lot of time ?

For instance Glut.idleFunc will do a search in the hashtable of caml 
names at each callback and if the callback was transmitted  through a C 
global variable there vould only be one indirection ?

I am about to change all the callback mechnism used in Glut. So if 
anyone knows a good reason to use names and hashtables ?

----- 8< ----- here is the code

----- First the caml code:


(* timerFunc is non-window-dependent *)
external _glutTimerFunc : int->((value:'a->'b) * 'a)->unit = 
"ml_glutTimerFunc"
let timerFunc ~ms ~cb ~value:v : (unit) =
     _glutTimerFunc ms (cb,v);; (* register the callback with GLUT *)

----- Then the C code:


--
// for timer we can not use Register.callback because it grows 
infinitely the
// number of global root

static void glutTimerFunc_cb(int fun_arg)
{
   // fun_arg is a pointer on a caml pair hidden in an integer.
   // Moreover we remove the global root because each callback is used once
   // by the timer.
   value *v = (value) fun_arg;
   leave_blocking_section ();
   value fun = Field(*v, 0);
   value arg = Field(*v, 1);
   caml_remove_global_root(v);
   free(v);
   callback (fun, arg);
   enter_blocking_section ();
}

CAMLprim value ml_glutTimerFunc(value millis_val, value fun_arg) // set 
Timer callback
{
   // fun_arg is a caml pair with a function and its argument we 
register a root on this pair and set the callback.
     unsigned int millis;
     value *v = (value*) malloc(sizeof(value));
     *v = fun_arg;
     caml_register_global_root(v);
     millis = Int_val(millis_val);
     glutTimerFunc(millis, &glutTimerFunc_cb, (int) v); // register with 
GLUT
     return Val_unit;
}

--
Christophe Raffalli
Université de Savoie
Batiment Le Chablais, bureau 21
73376 Le Bourget-du-Lac Cedex

tél: (33) 4 79 75 81 03
fax: (33) 4 79 75 87 42
mail: Christophe.Raffalli@univ-savoie.fr
www: http://www.lama.univ-savoie.fr/~RAFFALLI
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