On Sun, 5 Dec 2010 22:55:50 +0100
Ulrich Mueller <ulm@g.o> wrote:
> I don't understand the following passage from section "The state of
> the system between functions":

That whole section was written before Portage got parallel jobs
support, and was based around what ebuilds were actually doing.
Portage's parallel jobs break those rules, and this has caused all
kinds of weirdness.

The implications are *supposed* to be that if you want to do parallel
builds, you build binary packages in parallel (being sure to only run
one lot of pkg_ functions at once), and then install those binary
packages (the usual way, so rerunning pkg_setup) serially.

Instead, Portage just installs directly, and has a whole load of
convoluted hacks to try to avoid breakage. These don't actually work,
but the bugs are hidden often enough that you can often go for quite a
long time before you end up screwing your system up... In particular,
Portage assumes that if a and b aren't in any way dependent upon each
other, then they're not going to do anything to / that's going to break
the other one, which isn't true.

-- 
Ciaran McCreesh