Re: [PATCH 1/r47] maint: help2man targets should rely on the binaries they call.

[Ralf Wildenhues]

* Eric Blake wrote on Wed, Sep 22, 2010 at 08:30:08PM CEST:
> On 09/22/2010 12:22 PM, Ralf Wildenhues wrote:
> >* Eric Blake wrote on Wed, Sep 22, 2010 at 08:19:28PM CEST:
> >>  $(srcdir)/doc/libtool.1: $(srcdir)/$(auxdir)/ltmain.sh
> >>+   $(MAKE) libtool
> >>    $(update_mans) --help-option=--help-all libtool
> >
> >When -jN has been passed, the two makes may both try to update 'libtool'
> >at the same time, leading to a race.
> 
> Any ideas on how to avoid such a race?

1) .NOTPARALLEL:
Is not a good idea because it will make 'make -j3 check' slow again.  :-/

And if you require non-parallel builds, then you can again rely on the
fact that Posix make will update prerequisites in the order listed, so
that all you need to ensure is that all-am depends on 'libtool' earlier
than it depends on '$(srcdir)/doc/libtool.1'.

2) Use a subdir Makefile.am in doc, as SUBDIRS is a serializer.  Update
the manpage in doc/Makefile.am, and have 'SUBDIRS = . doc' in toplevel
so that it is updated first.

3) GNU make could use order-only prerequisites, but that is far too
unportable, as many practical GNU make installations are too old still.

4) BUILT_SOURCES = libtool libtoolize

Wait ... we are using (4) already.  Why does it not work?
IOW, I don't see the failure mode which this patch is supposed to fix.
Please show a verbose make log exhibiting the failure.  I'm guessing
there is a different actual reason for the failure.

Thanks,
ralf