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detecting logout
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detecting logout

This may be a Mac OS X question as opposed to a Darwin question.
Nevertheless, this is the only relevant place I know of to ask this

I am developing a per-user bootstrap daemon. This program used to be a
startup item, but for obscure reasons not relevant to the problem at hand,
it became necessary to morph it into a per-user bootstrap daemon (and not,
it should be noted, a global bootstrap daemon). The key difference between
the two forms of program for purposes of this discussion is that a startup
item launches once at startup and a per-user bootstrap daemon launches
whenever a user logs in. This means that there may be many instances of a
single per-user bootstrap daemon, which is fine. The trick is knowing when
each instance should quit. When the user logs out, per-user bootstrap
daemons are not automagically killed, which I suppose may be a feature to
someone somewhere. For me, it presents a problem, because there is no reason
for an instance of my program to hang around after the user logs out. The
trick is knowing when that is.

Apple's QA1133 seems to be the available wisdom on knowing when users login
and logout.

Unfortunately, this QA seems to be out of date. It seems to describe the
pre-Panther, pre-Fast User Switching universe. QA1133 tells us we are to
believe the user is logging out when the user name is NULL, but, under
Panther, if user 1 logs in, user 2 logs in, and then user 2 logs out, at no
time will the console user be NULL. Even when the user is re-authenticating
to switch back to user 1, the console user is "loginwindow" as opposed to
NULL. (The user may be NULL after the *last* user logs out, but I haven't
tested this.)

I could enable the copious debug logging done by the distributed
notification server and maybe pick out some choice undocumented strings as
they fly around in the system and hope to interpret their meaning correctly,
but that seems unlikely to be future-proof.

If I must resort to higher-level APIs, I'd prefer Carbon-oriented solutions
rather than Cocoa-oriented solutions because the app in question is written
in C++, but I'll settle in a pinch for anything that works cleanly without
pulling me up into being a client of the window server.

Any ideas?


    Pete Gontier

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