Re: [Caml-list] Garbage collector woes

[Jeremy Yallop <yallop@gmail.com>]

On 4 July 2016 at 17:04, Christoph Höger <christoph.hoeger@tu-berlin.de> wrote:
> I have a program using OCaml callbacks, one of these callbacks looks is
> the following:
>
> /* Callbacks */
> CAMLprim iconv(void* user_data, double t, double const *x, double *cond) {
>   CAMLparam0();
>   CAMLlocal3(ml_t, ml_x, ml_cond);
>   const value desc = *((value*)user_data);

I'm guessing that 'desc' points to a block and N, MFIT and ICONV are
field accessors.

If so, you need to register 'desc' as a root here, since
caml_copy_double or caml_ba_alloc_dims could trigger a gc, moving desc
before it's next used.

It's probably also better not to call your exported function 'iconv',
since there's a POSIX function of that name.

>   /* Wrap the values in fresh big arrays */
>   ml_t = caml_copy_double(t);
>   ml_x = caml_ba_alloc_dims(CAML_BA_FLOAT64 | CAML_BA_C_LAYOUT, 1,
> (double*)x, Int_val(N(desc)));
>   ml_cond = caml_ba_alloc_dims(CAML_BA_FLOAT64 | CAML_BA_C_LAYOUT, 1,
> cond, Int_val(MFIT(desc)));
>
>   /* call the OCaml callback */
>   caml_callback3(ICONV(desc), ml_t, ml_x, ml_cond);
>   CAMLreturn0;
> }