On Wed, Jun 23 2021, Felipe Contreras wrote:
> Ævar Arnfjörð Bjarmason wrote:
>> As in db10fc6c09f this allows us to remove patterns of removing
>> leftover $@ files at the start of rules, since previous failing runs
>> of the Makefile won't have left those littered around anymore.
>>
>> I'm not as confident that we should be replacing the "mv $@+ $@"
>> pattern entirely, since that means that external programs or one of
>> our other Makefiles might race and get partial content.
>
> The reason I did it in db10fc6c09 is because both asciidoctor and
> asciidoc should deal with temporary files by themselves (like gcc). If
> you interrupt the build nothing gets generated.
If you interrupt the build default make behavior without
.DELETE_ON_ERROR kicks in.
My gcc 8.3.0 just does an unlink()/openat(..., O_RDWR|O_CREAT|O_TRUNC)
dance followed by chmod() when I do e.g.:
gcc -o main main.c
So no in-place atomic renaming, does yours do something different?
But yes, some tools do this themselves, I think in general it's less
annoying to deal with it yourself in a case like git's, because if they
do it their idea of an in-tree tempfile may not jive with your
.gitignore, so you'll racily see ghost files during build, or those
files getting left behind if the tool hard dies.
> However, other scripts like build-docdep.perl would indeed generate
> partial output.
>
> In my opinion it's the scripts themselves that should be fixed, and not
> the Makefile, *if* we care about this at all.
I don't think default tool/make/*nix semantics are broken, I just think
it's neat to do that rename dance yourself, it's a cheap way to
guarantee that we always have working tools for use by other concurrent
scripts.
Many build systems or modes of running them don't care about that
use-case.
