[gegl] tile-handler-empty: make it harder to dirty the empty common buffer

[Massimo Valentini <mvalentini src gnome org>]

commit 9131027658f4a56900181794c90d52f74d5320a2
Author: Massimo Valentini <mvalentini src gnome org>
Date:   Thu May 15 18:54:17 2014 +0200

    tile-handler-empty: make it harder to dirty the empty common buffer
    
    When the empty->tile was unreffed because its buffer was,
    a tile of an other buffer might become the only 'owner' of
    'common_buffer' which was possibly dirtied after unlocking
    this tile.
    
    By making every tile_handler_empty->tile sharing its
    data with a never ureffed tile it will be harder to legally
    dirty the 'common_buffer'

 gegl/buffer/gegl-tile-handler-empty.c |   18 +++++++++++-------
 1 files changed, 11 insertions(+), 7 deletions(-)
---
diff --git a/gegl/buffer/gegl-tile-handler-empty.c b/gegl/buffer/gegl-tile-handler-empty.c
index e85f668..d6dffbd 100644
--- a/gegl/buffer/gegl-tile-handler-empty.c
+++ b/gegl/buffer/gegl-tile-handler-empty.c
@@ -45,8 +45,8 @@ finalize (GObject *object)
 static GeglTile *
 _new_empty_tile (const gint tile_size)
 {
+  static GeglTile   *common_tile = NULL;
   static const gint  common_empty_size = sizeof (gdouble) * 4 * 128 * 128;
-  static guchar     *common_buffer = NULL;
 
   GeglTile *tile;
 
@@ -60,19 +60,23 @@ _new_empty_tile (const gint tile_size)
     }
   else
     {
-      if (!common_buffer && g_once_init_enter (&common_buffer))
+      if (!common_tile && g_once_init_enter (&common_tile))
         {
+          GeglTile *allocated_tile = gegl_tile_new_bare ();
           guchar *allocated_buffer = gegl_malloc (common_empty_size);
           memset (allocated_buffer, 0x00, common_empty_size);
-          g_once_init_leave (&common_buffer, allocated_buffer);
+
+          allocated_tile->data           = allocated_buffer;
+          allocated_tile->destroy_notify = NULL;
+          allocated_tile->size           = common_empty_size;
+          allocated_tile->is_zero_tile   = 1;
+
+          g_once_init_leave (&common_tile, allocated_tile);
         }
 
-      tile = gegl_tile_new_bare ();
+      tile = gegl_tile_dup (common_tile);
 
-      tile->destroy_notify = NULL;
-      tile->data = common_buffer;
       tile->size = tile_size;
-      tile->is_zero_tile = 1;
     }
 
   return tile;