[gentoo-dev] parallel fun in src_install - going beyond the serial monotony of 'make install'

[Robin H. Johnson]

In the present devmanual, for src_install, it notes that 
	make install DESTDIR="${D}"
is the preferred way to fire off the install, and to not use emake, for
fear of parallel issues.

This has four nasty side effects:
- Global assumption that make is GNU Make (Hi flameeyes).
- Doesn't pass MAKEOPTS for options other than -jX.
- Removes ability to use EXTRA_EMAKE.
- Large package installs are make very slow.

I did a bit of checking of a random selection of packages (looking at
the Makefile and internal dependancy trees, as well as a test with -j7
on my 4-way box), and found very few problems with the concept of
parallel installs.

For a start, practically all Makefiles generated by a recent version
(newer than 2001 for definite) are parallel safe. There are a few minor
cases I saw where this wasn't true, but those packages also had other
parallel build problems.

For packages that are definitely aren't parallel-install safe, we should
use 'emake -j1', just like the src_compile phase.

I'm not saying we should change the entire existing tree, but for new
packages, please consider emake for your src_install phase.

A nice use for EXTRA_EMAKE while debugging is being able to pass in
--debug=basic to make, and have it tell you why it rebuilt a target in
src_install, since src_install should not be compiling things ;-).

To forestall one question I expect, I'd like to point a basic fact about
how Makefiles work:
Multiple commands in a single target will always be executed in series,
and not parallel - so this target will work fine:
install:
   mkdir -p $(DESTDIR)/bin
   cp -f bar $(DESTDIR)/bin

-- 
Robin Hugh Johnson
E-Mail     : robbat2@g.o
GnuPG FP   : 11AC BA4F 4778 E3F6 E4ED  F38E B27B 944E 3488 4E85