Since not all the buildsystem we support use make for the actual build,
and they don't necessarily support make-like options (-jX -s and so on),
it would be nice to be able to express a JOBS variable that could be
used for parallel build with any build systems.

Right now there are ebuilds like openoffice or some scons-based ebuilds
that parse MAKEOPTS and get out of that the number of jobs from the -j
option, but this is a) suboptimal b) error-prone.

One has to consider people might be using -l for parallel building too,
for which reasons I'd be suggesting doing something like this to make
the change transparent:

 - ebuilds using non-make build systems would use JOBS;
 - ebuilds using make builds systems would just use emake as usual;
 - Portage takes care, if JOBS is unset, to parse it out of MAKEOPTS;
 - if user has set JOBS but not MAKEOPTS this defaults to -j${JOBS};
 - if user has JOBS and MAKEOPTS, MAKEOPTS keeps the same (for -l).

The result is that you can finally combine -l with parallel build on
OpenOffice and other packages, with a fallback number of maximum jobs
instead of using load-based decisions.

-- 
Diego "Flameeyes" Pettenò
http://blog.flameeyes.eu/