Re: [PATCH] GIT-VERSION-GEN: allow it to be run in parallel

From: Martin Ågren <martin.agren@gmail.com>
Date: Jan 9, 2025, 18:33 UTC
Message-ID: <CAN0heSo2pFmfx=zJgx2T6y+W1tG_PTXxf6uk2kBgi4c0kXz_oQ@mail.gmail.com>
In-Reply-To: <pull.1850.git.1736432663587.gitgitgadget@gmail.com>

On Thu, 9 Jan 2025 at 15:24, Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com> wrote:

Show 6 quoted lines

> And this is how that race surfaces: When calling `make -j2 html man`
> from the top-level directory (a variant of which is invoked in Git for
> Windows' release process), two sub-processes are spawned, a `make -C
> Documentation html` one and a `make -C Documentation man` one. Both run
> the rule to (re-)generate `asciidoctor-extensions.rb` or
> `asciidoc.conf`, invoking `GIT-VERSION-GEN` to do so.

Nicely described. Indeed, there's a reason recursive make is considered harmful. This is of course not the time or place for addressing that.

Show 7 quoted lines

> Incidentally, this also fixes something else: The `+` character is
> not even a valid filename character on Windows. The only reason why Git
> for Windows did not need this is that above-mentioned POSIX emulation
> layer also plays a couple of tricks with filenames (tricks that are not
> interoperable with regular Windows programs, though), and previous
> attempts to remedy this in git/git were unsuccessful, see e.g.
> https://lore.kernel.org/git/pull.216.git.gitgitgadget@gmail.com/

Show 12 quoted lines

> -       "$INPUT" >"$OUTPUT"+
> +       "$INPUT" >"$OUTPUT".$$
>
> -if ! test -f "$OUTPUT" || ! cmp "$OUTPUT"+ "$OUTPUT" >/dev/null
> +if ! test -f "$OUTPUT" || ! cmp "$OUTPUT".$$ "$OUTPUT" >/dev/null
>  then
> -       mv "$OUTPUT"+ "$OUTPUT"
> +       mv "$OUTPUT".$$ "$OUTPUT"
>  else
> -       rm "$OUTPUT"+
> +       rm "$OUTPUT".$$
>  fi

Our `.gitignore` contains an entry "*+" to ignore this sort of temporary files. Yes, they're supposed to disappear within a second or so, but according to f9bbaa384e (Add intermediate build products to .gitignore, 2009-11-08), they can linger after interrupted builds. Maybe separate tooling built around git could pick up these as untracked files for a second, causing them to come and go in whatever GUI.

You could use "$OUTPUT"."$$"+ to restore this. That of course invalidates your remark about "Incidentally, ..." above, but might give this fix a tiny bit less chance of regressing something somewhere?

Martin