Date: Thu, 30 Nov 2006 14:19:38 +0100
From: Maxence Guesdon <maxence.guesdon at inria.fr>
To: "Olivier Andrieu" <oandrieu at nerim.net>
Cc: lablgtk at math.nagoya-u.ac.jp
Subject: Re: strange behaviour of GMain.Main.main / GMain.Main.quit
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On Thu, 30 Nov 2006 10:16:48 +0100 (CET)
"Olivier Andrieu" <oandrieu at nerim.net> wrote:

> > On Wed, 29 Nov 2006 19:49:53 +0100
> > Olivier Andrieu <oandrieu@nerim.net> wrote:
> >
> >> Salut Maxence,
> >
> > Salut Olivier,
> >
> >>  Maxence Guesdon [Wednesday 29 November 2006] :
> >>  >
> >>  > Hello,
> >>  >
> >>  > I'm experiencing problems while using GMain.Main.main and
> >>  > GMain.Main.quit. Here is a program to reproduce the problem. It
> >>  > creates a window. When "Return" is pressed, the nb_waits counter in
> >>  > incrementend, then GMain.Main.main is called to wait for a
> >>  > GMain.Main.quit, then "pop!" is displayed (that is, when
> >>  > GMain.Main.main returns). When "Escape" is pressed, GMain.Main.quit
> >> is
> >>  > called nb_waits times. I thought that then all waiting "pop!" would
> >> be
> >>  > displayed one after the other but it works only when there is only
> >> one
> >>  > GMain.Main.main waiting. Is this a bug or a feature ?
> >>
> >> It's not a bug, that's just how the glib event loop API works. A
> >> GMainLoop has a is_running boolean flag. g_main_loop_run basically
> >> does a:
> >>   while (loop->is_running) process_events (loop);
> >> and g_main_loop_quit simply sets loop->is_running to FALSE.
> >>
> >> To get this multiple level of loops, you'd need to create a new loop
> >> object or something (but lablgtk doesn't wrap all the necessary
> >> functions).
> >
> > Looking at the code in GtkMain, I see:
> >   let loops = ref []
> >   let default_main () =
> >     let loop = (Main.create true) in
> >     loops := loop :: !loops;
> >     while Main.is_running loop do Main.iteration true done;
> >     if !loops <> [] then loops := List.tl !loops
> >   let main_func = ref default_main
> >   let main () = !main_func ()
> >   let quit () = if !loops <> [] then Main.quit (List.hd !loops)
> >
> > So it seems that when I call GMain.Main.main () a new loop is created
> > and it is destroyed when I call GMain.Main.quit (). Am I missnig
> > something ? What happens to the code after the call to GMain.Main.main
> > () in my example ?
> 
> Oh right, I forgot lablgtk was doing its own thing with loops rather than
> wrapping g_main_loop run.
> 
> Well what's happening in your code is that you're repeatedly calling
> GtkMain.Main.quit() in a for loop, but that turns into repeated calls to
> Glib.Main.quit() to the *same* loop object on top of the loops "stack". As
> you can see in the code above, loops are not pop'ed by GtkMain.Main.quit()
> but when GtkMain.Main.main() returns.

I understand now. For information, below is a new program doing as expected.
The important thing is in the wait function: After returning from the
GMain.Main.main (), it triggers another GMain.Main.quit if there are other
"waiters" remaining. Doing so, each GMain.Main.quit impacts the correct
event loop.

Merci Olivier ;-)

=========
GMain.Main.init ();;
let w = GWindow.window ~title:"test" ~width: 600 ~height: 400 ();;
let nb_waits = ref 0;;

let wait () =
  incr nb_waits;
  prerr_endline (Printf.sprintf "nb_waits is now %d" !nb_waits);
  GMain.Main.main ();
  if !nb_waits > 0 then
    begin
      decr nb_waits;
      GMain.Main.quit ()
    end 

let cb ev =
  let key = GdkEvent.Key.keyval ev in
  if key = GdkKeysyms._Return then
    begin
      wait ();
      prerr_endline "pop!"
    end
  else
    (
     if key = GdkKeysyms._Escape then
       (
        decr nb_waits;
        GMain.Main.quit ();
       )
    );
  true
;;
ignore (w#event#connect#key_press ~callback: cb);;
w#show ();;
GMain.Main.main ()
======

-- 
Maxence Guesdon
http://yquem.inria.fr/~guesdon/
http://devel.inria.fr/rocq/