Re: how to enforce ordering on a set of targets?

[Robert P. J. Day]

On Thu, 27 Jan 2005, Noel Yap wrote:

> Robert P. J. Day wrote:
>
> > On Wed, 26 Jan 2005, Paul D. Smith wrote:
> >
> > ok, here's what i'm doing in a bit more detail.  it's a recursive
> > make, where i'm using a trick i saw (in the make manual, i think) that
> > allows me to process subdirectories in parallel.  in slightly
> > simplified form:
>
> IIUC, this "trick" is no longer necessary.

ok, i'm curious about this claim since i don't see how it can be
avoided.

AFAIK, the historical way to recursively process subdirectories was in
a loop:

  SUBDIRS = d1 d2 d3 d4 d5

and you could define a macro called, say, MAKE-SUBDIRS, as

  define
  MAKE-SUBDIRS
  @for d in $(SUBDIRS); \
  do \
        if test -d $$d; then \
                echo $(MAKE) -C $$d $@; \
                $(MAKE) -C $$d $@; \
        else \
                echo DIR $$d skipped; \
        fi; \
  done
  endef

and then define each action target with something like:

  clean:
        ${MAKE-SUBDIRS}

now, this would work but, as i read somewhere (the online make
manual?), the drawback is that you can't parallelize the processing of
the subdirectories.

  the alternative approach is to do something like this:

  SUBDIRS = d1 d2 d3 d4 d5
  TARGETS = clean configure build

  .PHONY: ${TARGETS} ${SUBDIRS}
  ${TARGETS}: ${SUBDIRS}                       (rule [1])

now, for each subdirectory, i might have a slightly invocation:

  d1:
        ${MAKE} -C d1 ${MAKECMDGOALS}

  d2:
        ${MAKE} -C d2 (options just for d2 perhaps) ${MAKECMDGOALS}

and so on.  now, i can call this makefile with

  $ make clean

and, based on rule [1] above, i should be able to process those
subdirectories in parallel, no?  which, AFAICT, i *can't* do using the
more common loop construct.

  am i misunderstanding this?  is there an easier way to get what i
want?

rday