Re: [gtk-list] gtk_widget_show() outside gtk_main()

[Erik Mouw <J A K Mouw its tudelft nl>]

On Thu, 29 Oct 1998 12:55:08 -0400 (AST), gtk-list@redhat.com (Aaron Campbell) wrote:
> I have a button widget in an application that is connected to a callback
> function which, among other things, starts a separate process via a
> standard fork() + execl() + waitpid() procedure. I want to display a note
> via a label notifying the user that files are transferring and to please
> wait.

waitpid() blocks your application, unless called with the WNOHANG option.
As long as your application blocks, the user interface will not be
updated. 

> The button is connected to this callback with the gtk_signal_connect()
> function. The first part of the function just does some checking and
> setup. Right after that I put in my label and issued a
> gtk_widget_show(label). Unfortunately it doesn't update the display until
> the separate process completes (ie after the waitpid). I also tried
> putting the labelling part in a separate function that is called first,
> then another function to start the transfer. That also didn't work.
> 
> I'm assuming the widget displays are only updated inside gtk_main()? Does
> anyone have any suggestions? I also tried gtk_widget_realize(), that
> didn't work either, obviously I don't yet understand what that feature is
> for. :)

A widget is indeed shown if its events are handled in gtk_main(). Try this
(from the GTK FAQ):


 while (gtk_events_pending())
   gtk_main_iteration();


after you gtk_widget_show()-ed your widget.

The correct loop will be something like:


  pid_t pid;
  int status;
  int stop = 0;

  gtk_widget_show(mywidget);

  pid = fork();   /* some ancient systems prefer vfork() */
  /* default fork + exec code */

  /* child code */

  /* parent does this: */

  while(stop == 0)
    {
      if(waitpid(pid, &status, WNOHANG) != 0)
        stop = 1;
 
       while (gtk_events_pending())
         gtk_main_iteration();
    }

  gtk_widget_hide(mywidget);
   
  /* evaluate child status */


Note: I have not tested this code. Have a look at the book "Advanced
programming in the UNIX environment" by Richard Stevens for more
information on process control (or just read the friendly manual).


Erik

-- 
J.A.K. (Erik) Mouw, Information and Communication Theory Group, Department
of Electrical Engineering, Faculty of Information Technology and Systems,
Delft University of Technology, PO BOX 5031,  2600 GA Delft, The Netherlands
Phone: +31-15-2785859  Fax: +31-15-2781843  Email J.A.K.Mouw@its.tudelft.nl
WWW: http://www-ict.its.tudelft.nl/~erik/