Re: Another version of instance-private-data [really!]

[Owen Taylor <otaylor redhat com>]

On Tue, 2003-03-04 at 23:04, Tim Janik wrote:

> > +/* The 2*sizeof(size_t) alignment here is borrowed from
> > + * GNU libc, so it should be good most everywhere.
> > + * It is more conservative than is needed on some 64-bit
> > + * platforms, but ia64 does require a 16-byte alignment.
> > + * The SIMD extensions for x86 and ppc32 would want a
> > + * larger alignment than this, but we don't need to
> > + * do better than malloc.
> > + */
> > +#define STRUCT_ALIGNMENT (2 * sizeof (gsize))
> > +#define ALIGN_STRUCT(offset) \
> > +      ((offset + (STRUCT_ALIGNMENT - 1)) & -STRUCT_ALIGNMENT)
> > +
> 
> there's alignment logic in the definition of
> SIZEOF_FUNDAMENTAL_INFO already implemented, it should be
> seperated and reused (and is well tested on a number of
> systems already, including ia64).

I don't see anything immediately usable. The SIZEOF_FUNDAMENTAL_INFO
stuff is relying on that the maximally aligned thing in 
GType is either a gpointer or a glong. 

An example of where we need larger alignment than
SIZEOF_FUNDAMENTAL_INFO is a 32-bit platform where doubles are 64-bit
and need to be naturally aligned (aligned on 64-bit boundaries)

We could reuse the stronger ALIGN_STRUCT macro for the fundamental-info
code, but that's going to waste space on a lot of platforms.

> > @@ -1424,7 +1449,7 @@ g_type_free_instance (GTypeInstance *ins
> >
> >    instance->g_class = NULL;
> >  #ifdef G_ENABLE_DEBUG
> > -  memset (instance, 0xaa, node->data->instance.instance_size);	/* debugging hack */
> > +  memset (instance, 0xaa, total_instance_size);	/* debugging hack */
> 
> i fail to see how this could compile, since you added total_instance_size
> to g_type_create_instance() only.

Good catch - accidental substitution leakage and I wasn't compiling
with --enable-debug. Though actually, we do want total_instance_size()
here's so I've split it out into a little inline function.

> > +void
> > +g_type_class_add_private (gpointer g_class,
> > +			  gsize    private_size)
> > +{
> > +  GType instance_type = ((GTypeClass *)g_class)->g_type;
> > +  TypeNode *node = lookup_type_node_I (instance_type);
> > +  gsize offset;
> > +
> > +  if (!node || !node->is_instantiatable || !node->data || node->data->class.class != (gpointer) g_class)
> 
> there's no need to cast g_class into a (gpointer) which it is already.

Fixed.

> > +gpointer
> > +g_type_instance_get_private (GTypeInstance *instance,
> > +			     GType          private_type)
> > +{
> > +  TypeNode *instance_node;
> > +  TypeNode *private_node;
> > +  TypeNode *parent_node;
> > +  gsize offset;
> > +
> > +  g_return_val_if_fail (instance != NULL && instance->g_class != NULL, NULL);
> > +
> > +  instance_node = lookup_type_node_I (instance->g_class->g_type);
> > +  if (G_UNLIKELY (!instance_node || !instance_node->is_instantiatable))
> > +    {
> > +      g_warning ("instance of invalid non-instantiatable type `%s'",
> > +		 type_descriptive_name_I (instance->g_class->g_type));
> > +      return NULL;
> > +    }
> > +
> > +  private_node = lookup_type_node_I (private_type);
> > +  if (G_UNLIKELY (!private_node || !private_node->is_instantiatable))
> > +    {
> > +      g_warning ("cannot retrieve private instant for non-instantiatable type '%s'",
> > +		 type_descriptive_name_I (private_type));
> > +      return NULL;
> > +    }
> 
> we better check whether private_node is a parent node of instance,
> rather than just checking whether it's instantiatable (which is
> a pretty arbitrary check for an assumed parent type), that is:
> 
>   if (G_UNLIKELY (!private_node ||
>                   private_node->n_supers > instance_node->n_supers ||
>                   instance_node->supers[instance_node->n_supers -
>                                         private_node->n_supers] !=
>                   NODE_TYPE (private_node)))
> 

Strikes me as a bit expensive, but I've gone ahead and done it...
I've added a NODE_IS_ANCESTOR() macro that I've used here
and in type_node_check_conformaties_UorL() to avoid duplicating the
logic.

[...]

> > +  parent_node = lookup_type_node_I (NODE_PARENT_TYPE (private_node));
> > +
> > +  g_assert (parent_node->data && parent_node->data->common.ref_count);
> 
> bad assertion, parent_node might be NULL if you request private data
> from a fundamental type instance.

> > +
> > +  offset = ALIGN_STRUCT (instance_node->data->instance.instance_size) + parent_node->data->instance.private_size;
> 
> so better do:
> 
>   offset = ALIGN_STRUCT (instance_node->data->instance.instance_size);
>   if (parent_node)
>     offset += ALIGN_STRUCT (parent_node->data->instance.private_size);
> (using ALIGN_STRUCT() in this place to correspond to the ALIGN_STRUCT()
> you used in g_type_class_add_private())

OK, I've done something like that. Although we've made sure that
lookup_type_node_I (G_TYPE_NONE) => NULL, it feels a little dirty
to me, so I've done 'if (NODE_PARENT_TYPE (private_node))' instead.

> > +
> > +  return (gpointer)((gchar *)instance + ALIGN_STRUCT (offset));
> 
> glib has a macro for this, so the code should read:
> 
>   return G_STRUCT_MEMBER_P (instance, offset);
> (ALIGN_STRUCT() not needed with the above if (parent_node) branch)

OK, changed.

New patch attached. I've also fixed some bugs in the preallocs > 0 case;
there is a subtlety there ... if instance size is, say 8 and private
size 1, then it's fine to malloc 9 bytes if we are malloc'ing a single
instance, but if we have an array of structures, then we need to malloc 
ALIGN_STRUCT(9) bytes for each or the later elements in the array won't
be properly aligned.

Regards,
                                         Owen

Index: docs/reference/gobject/gobject-sections.txt
===================================================================
RCS file: /cvs/gnome/glib/docs/reference/gobject/gobject-sections.txt,v
retrieving revision 1.23
diff -u -p -r1.23 gobject-sections.txt
--- docs/reference/gobject/gobject-sections.txt	9 Dec 2002 19:06:42 -0000	1.23
+++ docs/reference/gobject/gobject-sections.txt	5 Mar 2003 16:32:10 -0000
@@ -30,6 +30,7 @@ G_TYPE_FROM_CLASS
 G_TYPE_FROM_INTERFACE
 G_TYPE_INSTANCE_GET_CLASS
 G_TYPE_INSTANCE_GET_INTERFACE
+G_TYPE_INSTANCE_GET_PRIVATE
 G_TYPE_CHECK_INSTANCE
 G_TYPE_CHECK_INSTANCE_CAST
 G_TYPE_CHECK_INSTANCE_TYPE
@@ -52,6 +53,7 @@ g_type_class_ref
 g_type_class_peek
 g_type_class_unref
 g_type_class_peek_parent
+g_type_class_add_private
 g_type_interface_peek
 g_type_interface_peek_parent
 g_type_children
@@ -97,6 +99,7 @@ g_type_check_class_is_a
 g_type_check_is_value_type
 g_type_check_value
 g_type_check_value_holds
+g_type_instance_get_private
 g_type_test_flags
 g_type_name_from_instance
 g_type_name_from_class
Index: docs/reference/gobject/tmpl/gtype.sgml
===================================================================
RCS file: /cvs/gnome/glib/docs/reference/gobject/tmpl/gtype.sgml,v
retrieving revision 1.22
diff -u -p -r1.22 gtype.sgml
--- docs/reference/gobject/tmpl/gtype.sgml	7 Feb 2003 22:08:53 -0000	1.22
+++ docs/reference/gobject/tmpl/gtype.sgml	5 Mar 2003 16:32:10 -0000
@@ -462,6 +462,17 @@ Returns the interface structure for inte
 @c_type: The corresponding C type of @g_type.
 
 
+<!-- ##### MACRO G_TYPE_INSTANCE_GET_PRIVATE ##### -->
+<para>
+Gets the private structure for a particular type.
+The private structure must have added from the class_init
+function with g_type_class_add_private().
+</para>
+
+ instance: the instance of a type deriving from @private_type.
+ g_type: the type identifying which private data to retrieve.
+ c_type: The C type for the private structure.
+
 <!-- ##### MACRO G_TYPE_CHECK_INSTANCE ##### -->
 <para>
 
@@ -693,6 +704,48 @@ g_type_class_peek (g_type_parent (G_TYPE
 @Returns: The parent class of @g_class.
 
 
+<!-- ##### FUNCTION g_type_class_add_private ##### -->
+<para>
+Registers a private structure for a instantiatable type;
+when an object is allocated, the private structures for
+the type and and all of its parent types are allocated
+sequentially in the same memory block as the public
+structures. This function should be called in the
+type's class_init() function. The private structure can
+be retrieved using the G_TYPE_INSTANCE_GET_PRIVATE() macro.
+The following example shows attaching a private structure
+<structname>MyObjectPrivate</structname> to an object
+<structname>MyObject</structname> defined in the standard GObject
+fashion.
+</para>
+<programlisting>
+typedef struct _MyObjectPrivate MyObjectPrivate;
+
+struct _MyObjectPrivate {
+  int some_field;
+};
+
+&num;define MY_OBJECT_GET_PRIVATE(o)  \
+   (G_TYPE_INSTANCE_GET_PRIVATE ((o), MY_TYPE_OBJECT, MyObjectPrivate))
+
+static void
+my_object_class_init (MyObjectClass *klass)
+{
+  g_type_class_add_private (klass, sizeof (MyObjectPrivate));
+}
+
+static int
+my_object_get_some_field (MyObject *my_object)
+{
+  MyObjectPrivate *priv = MY_OBJECT_GET_PRIVATE (my_object);
+
+  return priv->some_field;
+}
+</programlisting>
+
+ g_class: class structure for an instantiatable type
+ private_size: size of private structure.
+
 <!-- ##### FUNCTION g_type_interface_peek ##### -->
 <para>
 Returns the #GTypeInterface structure of an interface to which the passed in 
@@ -751,7 +804,6 @@ Returns the prerequisites of an interfac
 @n_prerequisites: location to return the number of prerequisites, or %NULL
 @Returns: a newly-allocated zero-terminated array of #GType containing 
    the prerequisites of @interface_type
-<!-- # Unused Parameters # -->
 @Since: 2.2
 
 
Index: docs/reference/gobject/tmpl/param_value_types.sgml
===================================================================
RCS file: /cvs/gnome/glib/docs/reference/gobject/tmpl/param_value_types.sgml,v
retrieving revision 1.9
diff -u -p -r1.9 param_value_types.sgml
--- docs/reference/gobject/tmpl/param_value_types.sgml	7 Feb 2003 22:08:53 -0000	1.9
+++ docs/reference/gobject/tmpl/param_value_types.sgml	5 Mar 2003 16:32:10 -0000
@@ -840,7 +840,7 @@ See g_param_spec_internal() for details 
 @maximum:       maximum value for the property specified
 @default_value: default value for the property specified
 @flags:         flags for the property specified
- Returns:  a newly created parameter specification 
+ Returns:  a newly created parameter specification
 
 
 <!-- ##### FUNCTION g_value_set_double ##### -->
@@ -1557,6 +1557,6 @@ See g_param_spec_internal() for details 
 @element_spec:  a #GParamSpec describing the elements contained in 
                 arrays of this property, may be %NULL
 @flags:         flags for the property specified
- Returns: a newly created parameter specification 
+ Returns: a newly created parameter specification
 
 
Index: gobject/ChangeLog
===================================================================
RCS file: /cvs/gnome/glib/gobject/ChangeLog,v
retrieving revision 1.241
diff -u -p -r1.241 ChangeLog
--- gobject/ChangeLog	17 Feb 2003 20:17:17 -0000	1.241
+++ gobject/ChangeLog	5 Mar 2003 16:32:10 -0000
@@ -1,3 +1,9 @@
+Thu Feb 27 17:33:19 2003  Owen Taylor  <otaylor redhat com>
+
+	* gtype.[ch]: Add support for instance-private data. (#101959)
+	g_type_class_add_private(), g_type_instance_get_private(),
+	G_TYPE_INSTANCE_GET_PRIVATE().
+
 Mon Feb 17 20:59:47 2003  Tim Janik  <timj gtk org>
 
 	* gvalue.c (g_value_register_transform_func): don't assert the types
Index: gobject/gtype.c
===================================================================
RCS file: /cvs/gnome/glib/gobject/gtype.c,v
retrieving revision 1.59
diff -u -p -r1.59 gtype.c
--- gobject/gtype.c	7 Feb 2003 22:04:24 -0000	1.59
+++ gobject/gtype.c	5 Mar 2003 16:32:10 -0000
@@ -107,6 +107,18 @@ static GStaticRWLock            type_rw_
 						       sizeof (gpointer)), \
                                                   sizeof (glong)))
 
+/* The 2*sizeof(size_t) alignment here is borrowed from
+ * GNU libc, so it should be good most everywhere.
+ * It is more conservative than is needed on some 64-bit
+ * platforms, but ia64 does require a 16-byte alignment.
+ * The SIMD extensions for x86 and ppc32 would want a
+ * larger alignment than this, but we don't need to
+ * do better than malloc.
+ */
+#define STRUCT_ALIGNMENT (2 * sizeof (gsize))
+#define ALIGN_STRUCT(offset) \
+      ((offset + (STRUCT_ALIGNMENT - 1)) & -STRUCT_ALIGNMENT)
+
 
 /* --- typedefs --- */
 typedef struct _TypeNode        TypeNode;
@@ -182,6 +194,10 @@ struct _TypeNode
 #define	iface_node_set_dependants_array_W(n,d)	(type_set_qdata_W ((n), static_quark_dependants_array, (d)))
 #define	TYPE_ID_MASK				((GType) ((1 << G_TYPE_FUNDAMENTAL_SHIFT) - 1))
 
+#define NODE_IS_ANCESTOR(ancestor, node)                                                    \
+        ((ancestor)->n_supers <= (node)->n_supers &&                                        \
+	 (node)->supers[(node)->n_supers - (ancestor)->n_supers] == NODE_TYPE (ancestor))
+
 
 struct _IFaceHolder
 {
@@ -229,6 +245,7 @@ struct _InstanceData
   gconstpointer      class_data;
   gpointer           class;
   guint16            instance_size;
+  guint16            private_size;
   guint16            n_preallocs;
   GInstanceInitFunc  instance_init;
   GMemChunk        *mem_chunk;
@@ -909,6 +926,13 @@ type_data_make_W (TypeNode              
       data->instance.class_data = info->class_data;
       data->instance.class = NULL;
       data->instance.instance_size = info->instance_size;
+      if (NODE_PARENT_TYPE (node))
+	{
+	  TypeNode *pnode = lookup_type_node_I (NODE_PARENT_TYPE (node));
+	  data->instance.private_size = pnode->data->instance.private_size;
+	}
+      else
+	data->instance.private_size = 0;
 #ifdef	DISABLE_MEM_POOLS
       data->instance.n_preallocs = 0;
 #else	/* !DISABLE_MEM_POOLS */
@@ -1338,6 +1362,19 @@ type_iface_blow_holder_info_Wm (TypeNode
     }
 }
 
+/* Assumes type's class already exists
+ */
+static inline size_t
+type_total_instance_size_I (TypeNode *node)
+{
+  gsize total_instance_size;
+
+  total_instance_size = node->data->instance.instance_size;
+  if (node->data->instance.private_size != 0)
+    total_instance_size = ALIGN_STRUCT (total_instance_size) + node->data->instance.private_size;
+
+  return total_instance_size;
+}
 
 /* --- type structure creation/destruction --- */
 GTypeInstance*
@@ -1347,6 +1384,7 @@ g_type_create_instance (GType type)
   GTypeInstance *instance;
   GTypeClass *class;
   guint i;
+  gsize total_instance_size;
   
   node = lookup_type_node_I (type);
   if (!node || !node->is_instantiatable)
@@ -1364,21 +1402,35 @@ g_type_create_instance (GType type)
     }
   
   class = g_type_class_ref (type);
+
+  total_instance_size = type_total_instance_size_I (node);
   
   if (node->data->instance.n_preallocs)
     {
       G_WRITE_LOCK (&type_rw_lock);
       if (!node->data->instance.mem_chunk)
-	node->data->instance.mem_chunk = g_mem_chunk_new (NODE_NAME (node),
-							  node->data->instance.instance_size,
-							  (node->data->instance.instance_size *
-							   node->data->instance.n_preallocs),
-							  G_ALLOC_AND_FREE);
+	{
+	  /* If there isn't private data, the compiler will have already
+	   * added the necessary padding, but in the private data case, we
+	   * have to pad ourselves to ensure proper alignment of all the
+	   * atoms in the slab.
+	   */
+	  gsize atom_size = total_instance_size;
+	  if (node->data->instance.private_size)
+	    atom_size = ALIGN_STRUCT (atom_size);
+	  
+	  node->data->instance.mem_chunk = g_mem_chunk_new (NODE_NAME (node),
+							    atom_size,
+							    (atom_size *
+							     node->data->instance.n_preallocs),
+							    G_ALLOC_AND_FREE);
+	}
+      
       instance = g_chunk_new0 (GTypeInstance, node->data->instance.mem_chunk);
       G_WRITE_UNLOCK (&type_rw_lock);
     }
   else
-    instance = g_malloc0 (node->data->instance.instance_size);	/* fine without read lock */
+    instance = g_malloc0 (total_instance_size);	/* fine without read lock */
   for (i = node->n_supers; i > 0; i--)
     {
       TypeNode *pnode;
@@ -1424,7 +1476,7 @@ g_type_free_instance (GTypeInstance *ins
   
   instance->g_class = NULL;
 #ifdef G_ENABLE_DEBUG  
-  memset (instance, 0xaa, node->data->instance.instance_size);	/* debugging hack */
+  memset (instance, 0xaa, type_total_instance_size_I (node));	/* debugging hack */
 #endif  
   if (node->data->instance.n_preallocs)
     {
@@ -2255,8 +2307,7 @@ type_node_check_conformities_UorL (TypeN
   gboolean match;
   
   if (/* support_inheritance && */
-      iface_node->n_supers <= node->n_supers &&
-      node->supers[node->n_supers - iface_node->n_supers] == NODE_TYPE (iface_node))
+      NODE_IS_ANCESTOR (iface_node, node))
     return TRUE;
   
   support_interfaces = support_interfaces && node->is_instantiatable && NODE_IS_IFACE (iface_node);
@@ -3024,4 +3075,84 @@ void 
 g_type_init (void)
 {
   g_type_init_with_debug_flags (0);
+}
+
+void
+g_type_class_add_private (gpointer g_class,
+			  gsize    private_size)
+{
+  GType instance_type = ((GTypeClass *)g_class)->g_type;
+  TypeNode *node = lookup_type_node_I (instance_type);
+  gsize offset;
+
+  if (!node || !node->is_instantiatable || !node->data || node->data->class.class != g_class)
+    {
+      g_warning ("cannot add private field to invalid (non-instantiatable) type '%s'",
+		 type_descriptive_name_I (instance_type));
+      return;
+    }
+
+  if (NODE_PARENT_TYPE (node))
+    {
+      TypeNode *pnode = lookup_type_node_I (NODE_PARENT_TYPE (node));
+      if (node->data->instance.private_size != pnode->data->instance.private_size)
+	{
+	  g_warning ("g_type_add_private() called multiple times for the same type");
+	  return;
+	}
+    }
+  
+  G_WRITE_LOCK (&type_rw_lock);
+
+  offset = ALIGN_STRUCT (node->data->instance.private_size);
+  node->data->instance.private_size = offset + private_size;
+  
+  G_WRITE_UNLOCK (&type_rw_lock);
+}
+
+gpointer
+g_type_instance_get_private (GTypeInstance *instance,
+			     GType          private_type)
+{
+  TypeNode *instance_node;
+  TypeNode *private_node;
+  TypeNode *parent_node;
+  gsize offset;
+
+  g_return_val_if_fail (instance != NULL && instance->g_class != NULL, NULL);
+  
+  instance_node = lookup_type_node_I (instance->g_class->g_type);
+  if (G_UNLIKELY (!instance_node || !instance_node->is_instantiatable))
+    {
+      g_warning ("instance of invalid non-instantiatable type `%s'",
+		 type_descriptive_name_I (instance->g_class->g_type));
+      return NULL;
+    }
+
+  private_node = lookup_type_node_I (private_type);
+  if (G_UNLIKELY (!private_node || !NODE_IS_ANCESTOR (private_node, instance_node)))
+    {
+      g_warning ("attempt to retrieve private data for invalid type '%s'",
+		 type_descriptive_name_I (private_type));
+      return NULL;
+    }
+
+  /* Note that we don't need a read lock, since instance existing
+   * means that the instance class and all parent classes
+   * exist, so the node->data, node->data->instance.instance_size,
+   * and node->data->instance.private_size are not going to be changed.
+   * for any of the relevant types.
+   */
+
+  offset = ALIGN_STRUCT (instance_node->data->instance.instance_size);
+
+  if (NODE_PARENT_TYPE (private_node))
+    {
+      parent_node = lookup_type_node_I (NODE_PARENT_TYPE (private_node));
+      g_assert (parent_node->data && parent_node->data->common.ref_count);
+
+      offset += ALIGN_STRUCT (parent_node->data->instance.private_size);
+    }
+
+  return G_STRUCT_MEMBER_P (instance, offset);
 }
Index: gobject/gtype.h
===================================================================
RCS file: /cvs/gnome/glib/gobject/gtype.h,v
retrieving revision 1.47
diff -u -p -r1.47 gtype.h
--- gobject/gtype.h	3 Dec 2002 23:54:54 -0000	1.47
+++ gobject/gtype.h	5 Mar 2003 16:32:10 -0000
@@ -150,6 +150,8 @@ struct _GTypeQuery
 #define G_TYPE_FROM_CLASS(g_class)                              (((GTypeClass*) (g_class))->g_type)
 #define G_TYPE_FROM_INTERFACE(g_iface)                          (((GTypeInterface*) (g_iface))->g_type)
 
+#define G_TYPE_INSTANCE_GET_PRIVATE(instance, g_type, c_type)   ((c_type*) g_type_instance_get_private ((GTypeInstance*) (instance), (g_type)))
+
 
 /* debug flags for g_type_init_with_debug_flags() */
 typedef enum	/*< skip >*/
@@ -298,6 +300,10 @@ void  g_type_interface_add_prerequisite 
 GType *g_type_interface_prerequisites   (GType                       interface_type,
 					 guint                       *n_prerequisites);
 
+void     g_type_class_add_private    (gpointer       g_class,
+				      gsize          private_size);
+gpointer g_type_instance_get_private (GTypeInstance *instance,
+				      GType          private_type);
 
 /* --- protected (for fundamental type implementations) --- */
 GTypePlugin*	 g_type_get_plugin		(GType		     type);
Index: gobject/testgobject.c
===================================================================
RCS file: /cvs/gnome/glib/gobject/testgobject.c,v
retrieving revision 1.6
diff -u -p -r1.6 testgobject.c
--- gobject/testgobject.c	12 Oct 2002 20:04:58 -0000	1.6
+++ gobject/testgobject.c	5 Mar 2003 16:32:10 -0000
@@ -126,8 +126,10 @@ iface_print_string (TestIface   *tiobj,
 #define TEST_IS_OBJECT(object)      (G_TYPE_CHECK_INSTANCE_TYPE ((object), TEST_TYPE_OBJECT))
 #define TEST_IS_OBJECT_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), TEST_TYPE_OBJECT))
 #define TEST_OBJECT_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), TEST_TYPE_OBJECT, TestObjectClass))
-typedef struct _TestObject      TestObject;
-typedef struct _TestObjectClass TestObjectClass;
+#define TEST_OBJECT_GET_PRIVATE(o)  (G_TYPE_INSTANCE_GET_PRIVATE ((o), TEST_TYPE_OBJECT, TestObjectPrivate))
+typedef struct _TestObject        TestObject;
+typedef struct _TestObjectClass   TestObjectClass;
+typedef struct _TestObjectPrivate TestObjectPrivate;
 struct _TestObject
 {
   GObject parent_instance;
@@ -140,6 +142,11 @@ struct _TestObjectClass
 			 TestIface  *iface_object,
 			 gpointer    tdata);
 };
+struct _TestObjectPrivate
+{
+  int     dummy1;
+  gdouble dummy2;
+};
 static void	test_object_class_init	(TestObjectClass	*class);
 static void	test_object_init	(TestObject		*tobject);
 static gboolean	test_signal_accumulator	(GSignalInvocationHint	*ihint,
@@ -190,10 +197,18 @@ test_object_class_init (TestObjectClass 
 		test_signal_accumulator, NULL,
 		g_cclosure_marshal_STRING__OBJECT_POINTER,
 		G_TYPE_STRING, 2, TEST_TYPE_IFACE, G_TYPE_POINTER);
+
+  g_type_class_add_private (class, sizeof (TestObjectPrivate));
 }
 static void
 test_object_init (TestObject *tobject)
 {
+  TestObjectPrivate *priv;
+
+  priv = TEST_OBJECT_GET_PRIVATE (tobject);
+
+  g_assert (priv);
+  g_assert ((gchar *)priv >= (gchar *)tobject + sizeof (TestObject));
 }
 static gboolean
 test_signal_accumulator (GSignalInvocationHint *ihint,
@@ -274,8 +289,16 @@ derived_object_test_iface_init (gpointer
 #define DERIVED_IS_OBJECT(object)      (G_TYPE_CHECK_INSTANCE_TYPE ((object), DERIVED_TYPE_OBJECT))
 #define DERIVED_IS_OBJECT_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), DERIVED_TYPE_OBJECT))
 #define DERIVED_OBJECT_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), DERIVED_TYPE_OBJECT, DerivedObjectClass))
-typedef struct _TestObject      DerivedObject;
-typedef struct _TestObjectClass DerivedObjectClass;
+#define DERIVED_OBJECT_GET_PRIVATE(o)  (G_TYPE_INSTANCE_GET_PRIVATE ((o), DERIVED_TYPE_OBJECT, DerivedObjectPrivate))
+typedef struct _TestObject           DerivedObject;
+typedef struct _TestObjectClass      DerivedObjectClass;
+typedef struct _DerivedObjectPrivate DerivedObjectPrivate;
+struct _DerivedObjectPrivate
+{
+  char dummy;
+};
+static void derived_object_class_init (DerivedObjectClass *class);
+static void derived_object_init       (DerivedObject      *dobject);
 GType
 derived_object_get_type (void)
 {
@@ -288,12 +311,12 @@ derived_object_get_type (void)
 	sizeof (DerivedObjectClass),
 	NULL,           /* base_init */
 	NULL,           /* base_finalize */
-	NULL,		/* class_init */
+	(GClassInitFunc) derived_object_class_init,
 	NULL,           /* class_finalize */
 	NULL,           /* class_data */
 	sizeof (DerivedObject),
 	5,              /* n_preallocs */
-	NULL,		/* instance_init */
+	(GInstanceInitFunc) derived_object_init,
       };
       GInterfaceInfo iface_info = { derived_object_test_iface_init, NULL, GUINT_TO_POINTER (87) };
 
@@ -303,7 +326,28 @@ derived_object_get_type (void)
 
   return derived_object_type;
 }
+static void
+derived_object_class_init (DerivedObjectClass *class)
+{
+  g_type_class_add_private (class, sizeof (DerivedObjectPrivate));
+}
+static void
+derived_object_init (DerivedObject *dobject)
+{
+  TestObjectPrivate *test_priv;
+  DerivedObjectPrivate *derived_priv;
+
+  derived_priv = DERIVED_OBJECT_GET_PRIVATE (dobject);
 
+  g_assert (derived_priv);
+  g_assert ((gchar *)derived_priv >= (gchar *)TEST_OBJECT_GET_PRIVATE (dobject) + sizeof (TestObjectPrivate));
+
+  test_priv = TEST_OBJECT_GET_PRIVATE (dobject);
+  
+  g_assert (test_priv);
+  g_assert ((gchar *)test_priv >= (gchar *)dobject + sizeof (TestObject));
+
+}
 
 /* --- main --- */
 int