Re: GUI systems Kragen Sitaker (kragen@pobox.com)
Tue, 27 Jun 2000 21:29:52 -0400 (EDT)

Shap writes:
> > On restart after a "crash" is it really so
> > difficult for the GUI to iterate its list of programs and signal them to
> > redraw/invalidate?
>
> This is indeed how I have in mind to implement restart. The problem is that
> once you build redraw/invalidate into the GUI you tend to start using it for
> other purposes, and it becomes a potential covert channel.

Redraw will probably end up in the GUI anyway; I've never seen one without such an event, and even cursor-addressing-based applications almost always have a redraw. If you want to reduce its usefulness as a covert channel, you can be Plan9-crude and just send a bare redraw event devoid of additional information (like the size of the exposed region).

> There is another issue, which is more "purist" in nature: the number of
> programs that get notified of a restart should be kept as small as possible.

If I get a redraw event, I don't have any idea whether it's because I've been deiconified, because Netscape has been iconified, because the screen saver has just exited, because the user has invoked the "redraw screen" command, or because the system has restarted. 

-- 
<kragen@pobox.com>       Kragen Sitaker     <http://www.pobox.com/~kragen/>
The Internet stock bubble didn't burst on 1999-11-08.  Hurrah!
<URL:http://www.pobox.com/~kragen/bubble.html>
The power didn't go out on 2000-01-01 either.  :)