ERROR: could not load symbol "p4est_iter_fside_array_index_int": The specified procedure could not be found.

[Blumenkranz]

I got "ERROR: could not load symbol "p4est_iter_fside_array_index_int": The specified procedure could not be found." when I pass it a Ref(my_sc_array)

[JoshuaLampert]

Can you provide an MWE please?

[Blumenkranz]

Sure!

MPI.Init()
connectivity = p4est_connectivity_new_brick(2,2,0,0)
p4est = p4est_new_ext(MPI.COMM_WORLD, connectivity, 0, 1, 1,0,C_NULL, C_NULL)
p4est_iterate(p4est,C_NULL,C_NULL,C_NULL,@cfunction(show_face_info,Cvoid,(Ptr{p4est_iter_face_info_t},Ptr{Nothing})),C_NULL)
function show_face_info(info,data)
    ip = PointerWrapper(info)
    sides = Ptr{sc_array_t}(pointer_from_objref(Ref(ip.sides[])))
    side = p4est_iter_fside_array_index_int(sides,0)
    return nothing
end

[ranocha]

It looks like it's missing since it's declared as static inline:

/** Return a pointer to a iter_face_side array element indexed by a int.
 */
/*@unused@*/
static inline p4est_iter_face_side_t *
p4est_iter_fside_array_index_int (sc_array_t * array, int it)
{
  P4EST_ASSERT (array->elem_size == sizeof (p4est_iter_face_side_t));
  P4EST_ASSERT (it >= 0 && (size_t) it < array->elem_count);

  return (p4est_iter_face_side_t *)
    (array->array + sizeof (p4est_iter_face_side_t) * (size_t) it);
}

See https://github.com/cburstedde/p4est/blob/aafb87d93e33dffe24d67533d56bc2f0cdb72605/src/p4est_iterate.h#L265-L276

I'm not sure whether it's really considered to be part of the public API of p4est either.

[Blumenkranz]

The function is used in p4est's example:

static void
step3_upwind_flux (p4est_iter_face_info_t * info, void *user_data)
{
  int                 i, j;
  p4est_t            *p4est = info->p4est;
  step3_ctx_t        *ctx = (step3_ctx_t *) p4est->user_pointer;
  step3_data_t       *ghost_data = (step3_data_t *) user_data;
  step3_data_t       *udata;
  p4est_quadrant_t   *quad;
  double              vdotn = 0.;
  double              uavg;
  double              q;
  double              h, facearea;
  int                 which_face;
  int                 upwindside;
  p4est_iter_face_side_t *side[2];
  sc_array_t         *sides = &(info->sides);

  /* because there are no boundaries, every face has two sides */
  P4EST_ASSERT (sides->elem_count == 2);

  side[0] = p4est_iter_fside_array_index_int (sides, 0);
  side[1] = p4est_iter_fside_array_index_int (sides, 1);

See https://github.com/cburstedde/p4est/blob/master/example/steps/p4est_step3.c#L902
Can I achieve the same purpose with P4est.jl?

[ranocha]

The function does not seem to be included in the dynamic library, so you can't call it. You could just write the code in Julia - the function definition doesn't look too long.

[sloede]

AFAICT, the function must not be exported from the dynamic library since it is marked static, which indicates internal linkage. That is, variables and functions marked as such may only be visible in the current translation unit. Thus, there is no way that this function may be called from the p4est library.

Why the p4est developers chose to implement it in such a way is different question. My first guess would be for performance reasons, but that only explains the inline, not the static part. Maybe @cburstedde could shed some light on this?

[Blumenkranz]

I see. I'll write static functions in Julia. Thank you all for your help and time. And maybe we can add some explanation for these functions or just remove them from our API? The error can be confusing at the first time.

[ranocha]

Yes, I definitely understand the confusion. Does Clang.jl have an option to skip static functions?

[cburstedde]

Why the p4est developers chose to implement it in such a way is different question. My first guess would be for performance reasons, but that only explains the `inline`, not the `static` part. Maybe @cburstedde could shed some light on this?

Good observation, in fact all our inline functions are static. If they weren't, and the compiler would not be able to inline for whatever reason, we'd have multiple functions with the same external name in the library, which we tried to avoid back in the day as a precaution. I also understand that static functions cannot be called from the outside. These functions do not have much use outside of the p4est C interface, so I'm wondering if you might skip exporting them and keep them on the inside.

[sloede]

Thanks for the fast response and the explanation @cburstedde!

These functions do not have much use outside of the p4est C interface, so
I'm wondering if you might skip exporting them

Yes, that's a good suggestion. We are currently looking into whether this is feasible and how.