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Re: Text View Complaining about Double Free or Corruption

g_object_ref_sink() replaces gtk_object_sink() 

Please make this substitution

James, 


On Thu, 2008-02-28 at 00:04 -0500, James Scott Jr wrote:


On Wed, 2008-02-27 at 21:03 -0500, Mark Rodriguez wrote:


James,


 When doe s the error occur?
 0. When program starts
 1. When shutting down
 2. When creating the text_view the first time
 3. When creating the text_view the Nth time

 I will assume it happens durin shutdown (#1).


Yes you are correct. In the "real" application, the application
doesn't exit. It destroys the canvas and re-uses it with new controls.
Rather than debug that [monster], I reduced the application to
something more manageable that exhibit the same behavior.


 Yes, it should be handled like any other widget.  The only special thing is
its text_buffer!  Consider gtk_text_view_new_with_buffer(), one is created
automatically for when using the gtk_text_view_new() api.  I don't think
creating the GtkTextBuffer first would make any difference -- however, that
where you are now.  So try creating the GtkTextBuffer first, then use the
...with_buffer() api to create the view.  This may produce a different
result.


Interesting. I tried a few different things today and was able to get
the application to work as expected without crashing, but I don't like
the solution as now it appears I'm leaking memory. Any thoughts on why
if g_object_unref is called the application complains about the double
free? I modified the code as follows (mainly the button_click_event
handler was changed to handle the text buffer and to require clicking
the 'Quit' button twice for exiting the app - this was just done for
visibility reasons).



ref's are strange things: When I run into this anomaly I do the
following, reasoning that I must have only had a weak reference, and
g_object_unref got confused -- anyway this normally works for me.

/* creation code ... */
...
   buffer = gtk_text_buffer_new(NULL);
   if (buffer != NULL) {
             g_object_ref (G_OBJECT(buffer));
             gtk_object_sink (G_OBJECT(buffer));   
   }

sinking it ensures that you have a full fledged reference that a later
unref will honor.  

If your creating and deleting this text_view as needed, you will have to
find the root cause of these messages.  I notice that you prep'ed the
main() to use threads.  Your problem maybe related to how your using
threads when creating/destroying the text view.  I would suggest
exploring this type of change.  

1a. Only create/destroy in the main gtk/gdk thread.

1b. Fire off a g_timeout_add( 500000, (GSourceFunc)fn_create_routine(),
gpointer); where "gboolean fn_create_routine(gpointer gp);" calls the
normal gtk_window_new() stuff to create a dialog or the window you plan
to use the text_view in.  All this gets you out of the normal gtk signal
chain of events.  signals iterate on themselves and I've seen unwinds
cause random errors - like your double-free.

1c. Do essentially the same to destroy the window.

2a. I guess I don't actually delete/destroy main windows once created, I
just hide them and present them again when needed.
2b. Or if I do destroy them, i keep the buffer and/or tree_model in a
allocated memory structure.  Thus gtk_text_view_new_with_buffer() is the
type of call I most often use to create text_views.

3.  You seem to be _show() ing objects before adding them to something.
Look at vbox; you create it, show it, then add it to the main.window.
The recommended style is to create, add, show.   I don't think causes
any immediate problems but it could be polluting something- anyway this
strikes me as something worth cleaning up.


James,





[code]
GtkWidget *main_window, *text_view, *box, *button;
GtkTextBuffer* buffer;

static void destroy_event(GtkWidget* widget, void* data)
{
    gtk_main_quit();
}

static void button_click_event(void)
{
    if (text_view != NULL)
    {
            gtk_container_remove(GTK_CONTAINER(box), text_view);
            text_view = NULL;
            // leaking memory???
//          g_object_unref(G_OBJECT(buffer));
            buffer = NULL;
    }
    else
    {
            gtk_widget_destroy(main_window);
            main_window = NULL;
    }
}

int main(int argc, char* argv[])
{
    // initialize multi-threading within GLib
    g_thread_init(NULL);

    // initialize multi-threading within GDK
    gdk_threads_init();

    // acquire thread lock
    gdk_threads_enter();
    gtk_init(&argc, &argv);

    // create main window
    main_window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    if (main_window == NULL)
            abort();
    g_signal_connect(G_OBJECT(main_window), "destroy",
G_CALLBACK(destroy_event), NULL);
    gtk_widget_show(main_window);

    box = gtk_vbox_new(FALSE, 5);
    if (box == NULL)
            abort();
    gtk_widget_show(box);
    gtk_container_add(GTK_CONTAINER(main_window), box);

    buffer = gtk_text_buffer_new(NULL);
    if (buffer == NULL)
            abort();

    text_view = gtk_text_view_new_with_buffer(buffer);
    if (text_view == NULL)
            abort();
    gtk_widget_show(text_view);
    gtk_box_pack_start(GTK_BOX(box), text_view, TRUE, TRUE, 5);

    button = gtk_button_new_with_label("Quit");
    if (button == NULL)
            abort();
    g_signal_connect(G_OBJECT(button), "clicked",
G_CALLBACK(button_click_event), NULL);
    gtk_widget_show(button);
    gtk_box_pack_start(GTK_BOX(box), button, TRUE, TRUE, 5);

    // run the main loop
    gtk_main();

    // release thread lock
    gdk_threads_leave();

    return 0;
}
[/code]



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