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[Robert Lange <rcl24@xxxxxxxxxx>]

After getting really frustrated with this bug, I spent most of 4th of
July weekend wading knee-deep in gnome-session and gnome-screensaver
code, but I finally rooted out the bugs behind this.  There are two
bugs:

=== Bug 1 -- gnome-session -- gsm-manager.c ===

Gnome Screensaver activates when the Gnome Session Manager's Presence
module (gsm-presence.c) sends a StatusChanged signal over DBus.  This
signal is sent when an idle watch timer expires.  When the timer expires
and sends the signal, it needs to be reset.  One code path to reset it
is triggered when the screensaver activates or deactivates.
(Notification of this is via DBus message.)  Otherwise, resets are
triggered by calls from gsm-manager.c that happen when a) the GConf key
corresponding to screensaver timeout is changed (e.g., when the user
changes the timeout in the preferences dialog), or b) an inhibitor is
added or removed (e.g., when you watch a movie in vlc).

So, if the screensaver is disabled when the idle timer expires, nothing
will be able to reset the idle timer.  Furthermore, when the user re-
enables the screensaver, the timer is still inactive, so the screensaver
won't be called.  Only by taking some special action, such as logging
out&in, changing the screensaver timeout, or manually activating a
screensaver, will the timer be re-activated.

I have fixed this by adding a callback in gsm-manager.c that watches for
changes to the GConf key corresponding to the screensaver being enabled
(/apps/gnome-screensaver/idle_activation_enabled).  When this GConf key
is changed, the idle watch timer is reset.

=== Bug 2 -- gnome-screensaver -- gs-listener-dbus.c ===

The above explains why screensavers are not triggered at all after re-
enabling the screensaver.  However, even with that fix, the screensaver
fades out, but then snaps back to life as soon as the fade is done.

Gnome Screensaver activation is a 2-stage process: first, the gnome-
session presence module sends a DBus StatusChanged signal, {gs-
watcher-x11.c & gs-monitor.c} checks whether the screensaver is
inhibited, and if not, begins a fade-out for 10 seconds.  When the 10
seconds have expired, assuming the user has not interrupted the fade-out
by doing something, {gs-watcher-x11.c & gs-monitor.c} triggers the
screensaver activation.  Activation is actually initiated from gs-
listener-dbus.c.

Unfortunately, due to some convoluted and muddled logic in
listener_check_activation and gs_listener_set_session_idle, if the
screensaver is disabled when an idle session signal is received, the gs-
listener-dbus.c believes that the session is idle (i.e., the screensaver
is on), even though the screensaver is disabled.  Then, once the
screensaver is re-enabled and begins receiving more idle session
notifications, gs-listener-dbus.c ignores those notifications, because
it thinks the screensaver is already on!  However, the fade-outs operate
on a different, uncorrupted state variable, so they are unaffected.
Thus, the fade-out happens correctly, but at the moment that the
screensaver should activate, nothing happens and the session returns to
the desktop.

My fixes to gs-listener-dbus.c maintain the correct state for the
session_idle variable, and clean up the logic of the two mentioned
functions, while adding comments and debugging messages.

=== Conclusion ===

When both packages are patched and recompiled, the screensaver will
resume working correctly after it has been disabled and re-enabled.

The gnome-session patch is against gnome-session_2.30.0-0ubuntu1.  To
apply, drop it in gnome-session-2.30.0/debian/patches, append a line
containing the filename to gnome-session-2.30.0/debian/patches/series,
and rebuild.

The gnome-screensaver patch is against gnome-
screensaver_2.30.0-0ubuntu2.  To apply, drop it in gnome-
screensaver-2.30.0/debian/patches and rebuild.

I will work to get these patches in a state where they can be accepted
into Ubuntu and upstream.  If anyone knows more about the process and
could help, that would be appreciated.

** Attachment added: "110_gnome-session-2.30.0__gnome-session__gsm-manager.c"
   http://launchpadlibrarian.net/51443690/110_gnome-session-2.30.0__gnome-session__gsm-manager.c

-- 
Gnome Screensaver does not activate reliably
https://bugs.launchpad.net/bugs/241206
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