delayed session startup

[Simon Steinbeiss]

Hi everyone,

wegen Florian and me started working on session a few months ago we also
expected it to work that way.
However we learned that there were two internal modes: saved sessions and
the fallback session.
Irritatingly the fallback session was the de facto standard or default that
everyone used/uses who doesn't save his/her session.

Now the thing about the fallback session was that it just started all
applications at once, irrespective of the priority group. The reason
documented in the code was that this was "merely the fallback"...
So we dug deeper trying to understand what could be improved. One of the
major limitations of not using a saved session (which always respected the
priority groups) is that the unique application/process id that the session
uses to identify a process to see whether it can start the next one is
generated once the app is running. So at the first session start the
session manager doesn't know anything about the apps apart from some
metadata like start command and name. This is how it always is for the
fallback session - or one should probably rename it to default session.
So we introduced the - rather limited - version of prio groups for the
default session, without being able to properly trace an app or its exact
status, but at least launching programs in batches, with autostart apps
from the user coming last.

In theory one could probably change the approach in general and just so
what the default session does "once" and then stick to that, but that would
have implied even bigger code changes to something I don't know enough
about (a certain type of session management also seems to have been
deprecated upstream at gnome/Gtk).

The idea of doing this prio groups approach was that we would reduce race
conditions and indeed a few have already done away (e.h. between the panel
and xfsettingsd), but I guess a few others are still out there.
My feeling is that this may simply have been ignored in the past or maybe
the impact of those races has increased with Gtk3.

I hope this helped to clarify the current situation or status of session!
Cheers
Simon



Olivier Fourdan <fourdan at gmail.com> schrieb am Sa., 20. Juli 2019, 18:11:

> Hi
>
> On Sat, 20 Jul 2019 at 17:38, Olaf Hering <olaf at aepfle.de> wrote:
> >
> > A few weeks, or perhaps months, ago the session startup code was updated
> to use "priority groups". Since this time there are notable delays during
> fresh boot. I just checked the wall clock. It took about 16 seconds from
> visible X11 mouse cursor until the first app windoes from
> ~/.config/autostart appeared.
> >
> > I wonder if there is room to improve this. Does xfce4-session actually
> wait for events from the apps launched via xfce4-session.xml? How does it
> decide that the next priority group should be processed?
> >
> > Maybe xfce4 apps could send notifications back to xfce4-sessions that
> their own init process is done, so that xfce4-session could move on?
>
> That's how I expected it to work as well, but my observation tend to
> show not even the priority is respected, which is ... confusing and I
> think is causing most of the pain we are experiencing with the races
> at startup.
>
> See https://bugzilla.xfce.org/show_bug.cgi?id=15712 and
> https://bugzilla.xfce.org/show_bug.cgi?id=15725
>
> There is something seriously fishy there...
>
> Cheers,
> Olivier
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