Re: [PATCHv3 6/6] gdb/doc: fix parallel build of pdf and dvi files

[Pedro Alves <pedro@palves.net>]

On 2024-06-06 18:49, Andrew Burgess wrote:
> When building with 'make -j20 -C gdb/doc all-doc' I often see problems
> caused from trying to build some dvi files in parallel with some pdf
> files.  The problem files are: gdb.dvi and gdb.pdf; stabs.dvi and
> stabs.pdf; and annotate.dvi and annotate.pdf.
> 
> The problem is that building these files create temporary files in the
> local directory.  There's already a race here that two make threads
> might try to create these files at the same time.
> 
> But it gets worse, to avoid issues where a failed build could leave
> these temporary files in a corrupted state, and so prevent the next
> build from succeeding, the recipe for each of these files delete all
> the temporary files first, this obviously causes problems if some
> other thread has already started the build and is relying on these
> temporary files.
> 
> To work around this problem I propose we start using the --build flag
> for texi2dvi (which is the same tool used to create the pdf files).
> The --build flag allows for the temporary files to be placed into a
> sub-directory, e.g. creating gdb.pdf will create the temporary files
> in gdb.t2d/pdf/ and gdb.dvi uses gdb.t2d/dvi/, in this way the
> temporary files will never clash, and we can easily delete the
> specific sub-directory at the start of the recipe to ensure a
> successful build.
> 
> Very old versions of texi2dvi don't support --build, so I've added a
> configure check for this option.  If the option is not supported then
> we don't use it.  This means we fall back to placing temporary files
> in the local directory, which means parallel builds will remain
> broken.  The --build option is definitely present in texi2dvi version
> 6.1, from 2016, so any version after that should be fine.
> 

If we care about old versions enough to support them like this, then
couldn't we instead make the subdirectories ourselves and build there,
instead of using --build?  That way, we would only have one code path,
and it would work the same in new or old texi2dvi?

I mean, make the rule do something like:

  mkdir -p pdf && cd pdf && texi2dvi ...