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From: hreba <hreba@terra.com.br>
Newsgroups: comp.lang.ada
Subject: GTK and tasking (GNAT)
Date: Sat, 03 May 2014 17:30:08 -0300
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Date: 2014-05-03T17:30:08-03:00
List-Id: <comp.lang.ada>

I guess the following reveals my ignorance about GTK as well as about 
tasking, but anyway, still beginner.

I made a GTK window with a button and a text box. Upon pressing the 
button, the text box shall count to 10 in 0.5 s intervals.

Here follows my callback package (for the button callback function 
'Start', 'with'-clauses omitted):

-------------------------------------------------------------------
package Callback is

    type UserType is record
       txtBox:	Gtk.GEntry.Gtk_Entry;
    end record;

    package Handlers is new Gtk.Handlers.User_Callback
      (Widget_Type => Gtk.Widget.Gtk_Widget_Record,
       User_Type	=> UserType);

    procedure Start
      (widget: access Gtk.Widget.Gtk_Widget_Record'Class;
       event: Gdk.Event.Gdk_Event;
       ud: UserType);

end Callback;


package body Callback is

    procedure Start
      (widget: access Gtk.Widget.Gtk_Widget_Record'Class;
       event: Gdk.Event.Gdk_Event;
       ud: UserType) is

    begin
       for i in 1..10 loop
          Gtk.GEntry.Set_Text (ud.txtBox, Integer'Image(i));
          --Gtk.Widget.Queue_Draw (Gtk.Widget.Gtk_Widget(ud.txtBox));
          delay 0.5;
       end loop;
    end Start;

end Callback;

------------------------------------------------------------------

Now when I press the button nothing happens at first, and after 5 
seconds a "1" appears in the text box.
Uncommenting the QueueDraw line didn't change anything.

Searching for an explication, I thought perhaps somehow some 
display-update mechanism of GTK is suspended together with my main task 
during the delays. So I wrote a version using Ada tasks (for the first 
time in my life). Well, it didn't work either, exactly the same behavior.

Can somebody tell me what is wrong and how to do it right?

The source of the tasked version follows. The other callback function, 
'Quit' is connected to the 'delete' event of the main window.


---------------------------------------------------------------------
package Callback is

    type UserType is record
       txtBox:	Gtk.GEntry.Gtk_Entry;
    end record;


    package Handlers is new Gtk.Handlers.User_Callback
      (Widget_Type => Gtk.Widget.Gtk_Widget_Record,
       User_Type	=> UserType);

    package Return_Handlers is new Gtk.Handlers.Return_Callback
       (Widget_Type => Gtk.Widget.Gtk_Widget_Record,
        Return_Type => Boolean);

    function Quit (
        widget: access Gtk.Widget.Gtk_Widget_Record'Class;
        event: Gdk.Event.Gdk_Event) return Boolean;

    procedure Start
      (widget: access Gtk.Widget.Gtk_Widget_Record'Class;
       event: Gdk.Event.Gdk_Event;
       ud: UserType);

end Callback;



package body Callback is

    goon:	Boolean:= true;

    task Task2 is
       entry StartCounter (txtBox: Gtk.GEntry.Gtk_Entry);
       entry TermTask;		-- terminate task
    end Task2;

    task body Task2 is
    begin
       while goon loop
          select
             accept StartCounter (txtBox: Gtk.GEntry.Gtk_Entry) do
                for i in 1..10 loop
                   Gtk.GEntry.Set_Text (txtBox, Integer'Image(i));
                   Gtk.Widget.Queue_Draw (Gtk.Widget.Gtk_Widget(txtBox));
                   delay 0.5;
                end loop;
             end StartCounter;
          or
             accept TermTask do
                goon:= false;
             end TermTask;
          end select;
       end loop;
       Ada.Text_IO.Put_Line("Task2 terminating");
    end Task2;


    function Quit (
        widget: access Gtk.Widget.Gtk_Widget_Record'Class;
        event: Gdk.Event.Gdk_Event) return Boolean is
       --pragma Unreferenced (widget);
       pragma Unreferenced (event);
    begin
       Task2.TermTask;
       Gtk.Main.Main_Quit;
       return False;
    end Quit;


    procedure Start
      (widget: access Gtk.Widget.Gtk_Widget_Record'Class;
       event: Gdk.Event.Gdk_Event;
       ud: UserType) is
    begin
       Task2.StartCounter (ud.txtBox);
    end Start;

end Callback;

------------------------------------------------------------------------






-- 
Frank Hrebabetzky		+55 / 48 / 3235 1106
Florianopolis, Brazil