[cairo] For libsvg-cairo, glibc-detected corrupted double-linked list detected.

[charles]

在 2005-07-25一的 21:56 -0400，Jason Dorje Short写道：
> charles wrote:
> > Hi:
> > 
> > When I do some transformation before call svg_cairo_render, and error
> > '*** glibc detected *** corrupted double-linked list: 0x08eea120 ***' is
> > encountered. (If I no transformation is applied, this error is not
> > occurred.).
> 
> Is that supposed to be caused by this test program?  I don't see it.
> The only errors valgrind gives are uninitialized-data ones.  This error
> sounds like memory corruption overwriting some glib data (an "invalid
> write" in valgrind).
> 
> > My test program is very simple, so I think it might be caused by
> > 'libsvg-cairo'. (Forgive me if it is my fault).
> 
> One problem I notice is that cairo_image_surface_get_width has no checks
> on its input.  So code like the following:
> 
>     mmsr = cairo_image_surface_create_from_png("mm.png");
>     mmw = cairo_image_surface_get_width(mmsr);
>     mmh = cairo_image_surface_get_height(mmsr);
> 
> will simply crash if mm.png is not present.  I guess this might be
> intentional but it does make debugging harder.
> 
> Aside from this I think the problem is you never initialize (clear) the
> surface.  Thus pixels that aren't drawn to by any other operation end up
> with unitialized data.
> 
>     cairo_save (cr);
>     cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
>     cairo_paint (cr);
>     cairo_restore (cr);
> 
> Maybe image surfaces should be created "cleared" (all zeroed - either
> transparent or black depending on surface format).
> 
> Also you call cairo_destroy(cr) twice.
> 
> Finally I suggest using --num-callers=50 with valgrind (50 is the
> maximum).  Valgrind's default of 4 callers is often not useful.
> 
> -jason
> 

Hi Jason:

O, This is really my fault! It is caused by the second cairo_destroy
(cr). :)

Thanks for you prompt very very very much!.

Charles  July 26, 2005.