Problems with Screensavers and other activity sensitive demons.

[Lubos Lunak]

On Thursday 07 of June 2007, Carsten Haitzler wrote:
> On Thu, 07 Jun 2007 02:02:01 +1000 Graeme Gill <graeme2 at argyllcms.com>
> babbled:
>
> XScreenSaverSuspend(). it's there. it's engineered. it's documented. the
> problem lies  not in lack of engineering in the X11 department. its a very
> clean implementation and exactly what you need. if screensaver apps are
> hacking around the xscreensaver extension and not using
> XScreenSaverSelectInput() + XScreenSaverNotifyEvent's - then they need to
> be corrected ad they simply are not playing nice (tm).

 Actually, to my best knowledge, none of this is true, except for "it's there" 
and "it's documented". It's over-engineered, it's unmaintained and as a 
consequence it's broken. You can have a look at 
http://bugs.freedesktop.org/show_bug.cgi?id=1419 for why the XScreenSaver 
maintainer thinks it's broken, and if that's not enough I can dig in the KDE 
screensaver for more. Screensaver apps are hacking around the extension or 
just plain ignoring it because they have to.

> > To avoid this I went to the trouble in my application
> > of temporarily disabling the screensaver while it is running,
> > using the documented mechanism under X11 for doing this:
> > XSetScreenSaver(). It didn't take long to discover that
> > this in fact was ineffective on the Red Had clone system
> > I was testing on. Some investigation revealed that 
> > the screensaver favoured by that distribution (xscreensaver)
> > wasn't playing nice with X11, and in fact was ignoring
> > the X11 screensaver mechanism. Perusal of the authors
> > website indicated that he had no interest in fixing this
> > problem, but merely suggested that application such
> > as mine run the "xscreensaver-command -deactivate"
> > periodically. Since there seem no other easy to implement
> > way of disabling xscreensaver, added a fork() then execlp()
> > every 60 seconds to do this. Ugly but it worked.
> >
> > Recently I have had a report from a user indicating that
> > a screensaver had interrupted calibration of his display.
> > Enquiry revealed that it was a new screensaver, the
> > GnomeScreensaver. Perusal of it's web site indicated
> > that once again, it is not backwards compatible with
> > the X11 screensaver mechanism, and that it uses yet another
> > method of control, this time based on D-Bus. While this seems a
> > little better choice than the xscreensaver approach, the lack
> > of backwards compatibility is distressing, and the means of
> > signalling activity so that it doesn't trigger bodes poorly
> > for future compatibility. It apparently needs a
> > "dbus-send --dest=org.gnome.ScreenSaver /org/gnome/ScreenSaver
> > org.gnome.ScreenSaver.SimulateUserActivity" every so often (why does
> > "org.gnome.Screensaver have to be repeated 3 times in the dbus-send
> > syntax ? Surely once is enough!)
> >
> > This looks bad, as it seems certain that when someone develops
> > a KDE screensaver

 We already do have one :) , in fact we've had it for like 8 years at least. 
And it should suspend when either DPMS or the XScreensaver extension are 
suspended, so it's presumably missing from your list because nobody had to 
complain about it.

> > , org.kde.screensaver will need signalling, 
> > and when fred develops a new screensaver, com.fred.screensaver will
> > need signalling etc. And what about power monitoring demons ? Will
> > they each need to be named and known, and a long list added to
> > as people add new ones to the operating systems, each time triggering
> > a flood of support calls for applications such as mine ?
> >
> > There doesn't seem like there's much system level design going
> > on here, just each application having to look after itself.

 As already said in another answer, your best choice at this moment should be 
xdg-screensaver from xdg-utils.

-- 
Lubos Lunak
KDE developer
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