Is font face reference counting broken?

[Andreas Falkenhahn]

Thanks, then the behaviour makes sense. 

Is there any way to flush Cairo's font cache? I'm using a font saved to a temp file and I can't delete that temp file as long as it's still in use (Windows behaviour). So I'd really need to find a way to make Cairo release the hold onto the file so that I can delete the temp file.

On 15.05.2024 at 16:13 Behdad Esfahbod wrote:

> the font cache of cairo holds onto the face.


> behdad
> http://behdad.org/

> On Wed, May 15, 2024 at 8:00 AM Andreas Falkenhahn <andreas at falkenhahn.com> wrote:

> I've noticed that the font face reference counting behaves a little
> weird in Cairo. Take a look at this code:
>  
>          printf("REF COUNT A: %d\n",
> cairo_font_face_get_reference_count(fface));
>  
>          cairo_set_font_face(cr, fface);
>  
>          printf("REF COUNT B: %d\n",
> cairo_font_face_get_reference_count(fface));
>  
>          cairo_set_font_size(cr, 36);
>          cairo_show_glyphs(cr, g, 1);
>  
>          printf("REF COUNT C: %d\n",
> cairo_font_face_get_reference_count(fface));
>  
>          cairo_destroy(cr);
>          cairo_surface_destroy(surf);
>  
>          printf("REF COUNT D: %d\n",
> cairo_font_face_get_reference_count(fface));
>  
>          cairo_font_face_destroy(fface); 
>  
>          printf("REF COUNT E: %d\n",
> cairo_font_face_get_reference_count(fface));
>  
>  This prints the following here:
>  
>         REF COUNT A: 1
>         REF COUNT B: 2
>         REF COUNT C: 4
>         REF COUNT D: 3
>         REF COUNT E: 2
>  
>  The values for ref count A, B, C are look correct AFAICS but what
> about the ref count value D? As you can see, I get 3 for ref count D
> but shouldn't this be back to 1 at this stage? 
>  
>  Consequently, since ref count value D is still 3, the ensuing call
> to cairo_font_face_destroy() won't actually destroy the font face
> but just decrease its ref count to 2 but isn't this wrong?
>  
>  To me it looks like either cairo_destroy() or cairo_show_glyphs()
> don't unref the font face correctly. I'd expect that after
> cairo_destroy() returns the ref count should be back to 1, shouldn't it?
>  
>  Or am I doing/understanding something wrong here?
>  
>  I'm attaching the full little demo program.
>  
>  -- 
>  Best regards,
>   Andreas Falkenhahn                          mailto:andreas at falkenhahn.com


-- 
Best regards,
 Andreas Falkenhahn                            mailto:andreas at falkenhahn.com