Re: [Newbie] finalize/dispose and get/set_property

[Stefan Kost <ensonic hora-obscura de>]

Hi Laurent,

please see inline comments.
> hi all,
>
> I'm using GObject to do "Object Programing in C", I'm not using GTK.
> I search in the mailing-list archive and I didn't get what I'd like.
>
> I've got pragmatic questions, quite "simple" (although I don't 
> understand), in order to have basics for doing deeper things :
>
> 1.
> I know it's a redundant question but I still don't understand how to use 
> finalize() and dispose().
> I understand that dispose() is called when a g_object_unref() is called 
> and that finalize() is called when the last g_object_unref() is called.
>
> I've got a GObject Camera, with :
>
> struct _CameraPrivate {
>  Vector3 * mPosition;
>  // and other members   gboolean dispose_has_run;
> };
>
> Vector3 is a GObject, with no private struct (<- no need)
> struct _Vector3 {
>  GObject parent;
>  gfloat x, y, z;
>
>  gboolean dispose_has_run;
> };
>
>
> I don't know what to do when I unref a camera : g_object_unref (G_OBJECT 
> (camera));
> I'd like to unref camera->self->mPosition, but when? and How ?
> And when do I free mPosition (g_free (self->priv->mPosition)) ?
> (I don't use signal)
>
> I' tried to unref(mPosition) in the camera_dispose(), but i've got an 
> error.
>
>
> Here is my code :
>
>
> static void
> camera_instance_init (GTypeInstance   *instance,
>                         gpointer         g_class)
> {
>  Camera *self = (Camera *)instance;
>         self->priv = g_new (CameraPrivate, 1);
>
>  self->priv->mPosition =  g_new (Vector3, 1);
if the Vector3 thing is a GObject this should be
  self->priv->mPosition = g_object_new(<the Vector3 type>,NULL);

>  vector3_set(self->priv->mPosition, -1.15, 32.0, 43.75);   // or whatever
>
>  self->priv->dispose_has_run = FALSE;
> }
>
> //
> // what should I do ?
> // replace mPosition by v ? ( => unref(mPosition) & ref(v)  )
> // or like I do just change the members x, y and z ?
> //
here I recommend to use GObject properties. Reread the gobjet tutorial and watch 
out of g_object_class_install_property() and the _set_property(), 
_get_property() methods

> void camera_setPosition(Camera *a, Vector3 * v)
> {
>  a->priv->mPosition->x = v->x;
>  a->priv->mPosition->y = v->y;
>  a->priv->mPosition->z = v->z;
> }
>
>
> static void
> camera_dispose (GObject *obj)
> {
>  Camera *self = (Camera *)obj;
>
>  if (self->priv->dispose_has_run) {
>    // If dispose did already run, return.
>    return;
>  }
>         // Make sure dispose does not run twice
>  self->priv->dispose_has_run = TRUE;
>
>  g_print("|| camera dispose ||\n");
>
>    // In dispose, you are supposed to free all types referenced from this
>  // object which might themselves hold a reference to self. Generally,
>  // the most simple solution is to unref all members on which you own a
>  // reference.
>
> //
> // that why I try to unref mPosition
> //
>  g_object_unref (G_OBJECT ( self->priv->mPosition ));
> //
if you turn the g_new() in init() into a g_object_new() then this will work.
As a rule of the thumb, release all references in dispose() and release all 
memory in finalize().
>  // Chain up to the parent class
>  G_OBJECT_CLASS (parent_class)->dispose (obj);
> }
>
> static void
> camera_finalize (GObject *obj)
> {
>  Camera *self = (Camera *)obj;
>
>  g_print("*** camera finalize ***\n");
>
> //
> // what sould I do ? g_free or g_object_unref  (mPosition) ?
> //  g_free (self->priv->mPosition);
> //  g_object_unref (G_OBJECT (self->priv->mPosition) );
> //
>
>  g_free (self->priv);
>
>  /* Chain up to the parent class */
>  G_OBJECT_CLASS (parent_class)->finalize (obj);
> }
>
>
>
> result =>
>
> || camera dispose ||
>
> (process:15709): GLib-GObject-WARNING **: invalid unclassed pointer in 
> cast to `GObject'
>
> (process:15709): GLib-GObject-CRITICAL **: g_object_unref: assertion 
> `G_IS_OBJECT (object)' failed
> *** camera finalize ***


Stefan