From: quixoticsycophant@...
Date: 2006-11-02T01:20:20+09:00
Subject: Re: parallel tasks with rake ?


Wilson Bilkovich wrote:
> On 11/1/06, quixoticsycophant@yahoo.com <quixoticsycophant@yahoo.com> wrote:
> > I was excited to switch my makefile system to rake, but I just
> > noticed rake lacks a (GNU) make option I can't live without: -j4.
> > It's like "make & ; make & ; make & ; make &" but with the
> > parallel jobs properly synchronized.  On a quad-core machine this
> > makes a world of difference, being around four times faster than a
> > simple 'make'.
> >
> > As I understand it, rake should be able to determine which targets
> > can be built in parallel just as (GNU) make does.  rake's
> > multitask feature isn't quite right because it shouldn't be up to
> > the user to determine parallel vs non-parallel tasks.  In fact,
> > the user should probably never decide parallelism by fiat; even if
> > the user happens to be correct, it creates a maintenance problem
> > whereby additional tasks will eventually render the parallel
> > assertion false.
> >
> > Perhaps there is something I'm missing about 'multitask' ?
>
> How does Make figure out which jobs can be run in parallel? In my
> experience, it just runs everything in parallel, and things break when
> the tasks aren't safely parallelizable. (e.g. doing make -j4 install
> on a FreeBSD port)

The Make program figures it out from the dependency graph.
Unfortunately, the 'install' target you mention is a fake target which
depends on nothing.  Such uses of 'install' are common but incorrect.
As a workaround, 'install' (and any other wrongly written targets)
should be treated as a special case and should not be run with -j.