Re: [gtk-list] Memchunks again

[Soeren Sandmann <sandmann daimi au dk>]

Soeren Sandmann <sandmann@daimi.au.dk> writes:

> The following code segfaults. Do you have any idea why? The seqfault
> seems to go away if SIZE is less than 65513. It also goes away if
> G_ALLOC_ONLY is changed into G_ALLOC_AND_FREE.
> 
> #include <glib.h>
> 
> #define SIZE 65513
> 
> int
> main ()
> {
>   GMemChunk *chunk;
>   guint8 *t1, *t2;
>   gint i;
> 
>   chunk = g_mem_chunk_create (guint8[SIZE], 4, G_ALLOC_ONLY);
> 
>   t1 = g_chunk_new (guint8, chunk);
>   for (i=0; i<SIZE; i++)
>     t1[i] = 'a'; 
>   t2 = g_chunk_new (guint8, chunk);
> }

I think it is a bug in GLib because GMemChunk->area_size in certain
cases can be smaller than the atom_size. I think the following patch
fixes it:

RCS file: /cvs/gnome/glib/gmem.c,v
retrieving revision 1.15
diff -u -r1.15 gmem.c
--- glib/gmem.c 1999/07/24 18:50:55     1.15
+++ glib/gmem.c 1999/08/17 09:42:28
@@ -492,13 +492,13 @@
   mem_chunk->area_size = area_size;
   if (mem_chunk->area_size > MAX_MEM_AREA)
     mem_chunk->area_size = MAX_MEM_AREA;
-  while (mem_chunk->area_size < mem_chunk->atom_size)
-    mem_chunk->area_size *= 2;
   
   rarea_size = mem_chunk->area_size + sizeof (GMemArea) - MEM_AREA_SIZE;
   rarea_size = g_mem_chunk_compute_size (rarea_size);
+  while (rarea_size - (sizeof (GMemArea) - MEM_AREA_SIZE) < mem_chunk->atom_size)
+    rarea_size *= 2;
   mem_chunk->area_size = rarea_size - (sizeof (GMemArea) - MEM_AREA_SIZE);
-  
+
   /*
     mem_chunk->area_size -= (sizeof (GMemArea) - MEM_AREA_SIZE);
     if (mem_chunk->area_size < mem_chunk->atom_size)