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From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, Jeff King <peff@peff.net>,
	Johannes Schindelin <johannes.schindelin@gmx.de>,
	Jonathan Nieder <jrnieder@gmail.com>
Subject: Re: [PATCH v2 2/5] Makefile: rename scripts in-place, don't clobber
Date: Tue, 30 Mar 2021 01:28:01 +0200	[thread overview]
Message-ID: <87czvhmtfi.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <xmqqk0ppkdmd.fsf@gitster.g>


On Mon, Mar 29 2021, Junio C Hamano wrote:

> Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:
>
>> It'll also guard against any weird issues with e.g. a command that
>> wants to read GIT-PERL-DEFINES to generate one of the %.perl scripts
>> racing with either a concurrent instance of "make" that has partially
>> updated the file, or test-lib.sh dying with some particularly weird
>> error because GIT-BUILD-OPTIONS was partway through being updated when
>> it ran.
>
> If something like that happens, doesn't that indicate a bug in the
> dependency graph in the Makefile or the implementation of "make"?
> The generated file is depended on for the consumer to be able to use
> a non-stale version---so the consumer should not start before the
> generator finishes.

If everything we were building in the Makefile would be invoked via
other Makefile rules, yes. But if I run say (cd t && ./t0000-basic.sh)
I'm having test-lib.sh pick up one of those (possibly partial) files,
this guarantees they'll all be atomically updated.

> You may be able to hide the breakage coming from "partially written
> file is easily recognizable and the consumer would barf".  But I am
> afraid that you are introducing a problem harder to diagnose, i.e.
> "the consumer reads from a complete file so there is no syntax error
> or other things that easily tells you there is a breakage, but what
> is used is stale and not up to date".
>
> The same comment applies to this step.  I do not think it would
> break (other than adding intermediate crufts) the result if you
> generate into temporary and rename to final, but it is not clear
> to me what the point is in doing so.

I just think it makes sense to do this for consistency. So on "master"
we've got 65 hits for $@+ in the Makefile, at the end of this saga we've
got 100.

I think being consistent across the board makes things easier to read,
and in combination with the later ".DELETE_ON_ERROR" we can also drop
other copy/paste cruft.

  reply	other threads:[~2021-03-29 23:29 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-07 13:20 [PATCH] Makefile: generate 'git' as 'cc [...] -o git+ && mv git+ git' Ævar Arnfjörð Bjarmason
2021-03-07 20:41 ` Junio C Hamano
2021-03-08 12:38   ` Ævar Arnfjörð Bjarmason
2021-03-08 17:21     ` Junio C Hamano
2021-03-08 18:26     ` Jeff King
2021-03-29 16:20 ` [PATCH v2 0/5] Makefile: don't die on AIX with open ./git Ævar Arnfjörð Bjarmason
2021-03-29 16:20   ` [PATCH v2 1/5] Makefile: rename objects in-place, don't clobber Ævar Arnfjörð Bjarmason
2021-03-29 18:21     ` Junio C Hamano
2021-03-29 18:26       ` Junio C Hamano
2021-03-29 23:24       ` Ævar Arnfjörð Bjarmason
2021-03-30  0:21         ` Junio C Hamano
2021-03-31 14:17           ` Ævar Arnfjörð Bjarmason
2021-03-31 18:50             ` Junio C Hamano
2021-03-29 16:20   ` [PATCH v2 2/5] Makefile: rename scripts " Ævar Arnfjörð Bjarmason
2021-03-29 18:40     ` Junio C Hamano
2021-03-29 23:28       ` Ævar Arnfjörð Bjarmason [this message]
2021-03-29 16:20   ` [PATCH v2 3/5] Makefile: don't needlessly "rm $@ $@+" before "mv $@+ $@" Ævar Arnfjörð Bjarmason
2021-03-29 18:46     ` Junio C Hamano
2021-03-29 16:20   ` [PATCH v2 4/5] Makefile: add the ".DELETE_ON_ERROR" flag Ævar Arnfjörð Bjarmason
2021-03-29 18:51     ` Junio C Hamano
2021-03-29 23:31       ` Ævar Arnfjörð Bjarmason
2021-03-29 23:58         ` Junio C Hamano
2021-03-30 15:11         ` Jeff King
2021-03-30 18:36           ` Junio C Hamano
2021-03-31  6:58             ` Jeff King
2021-03-31 18:36               ` Junio C Hamano
2021-03-31 22:29                 ` Johannes Schindelin
2021-03-29 16:20   ` [PATCH v2 5/5] Makefile: don't "rm configure" before generating it Ævar Arnfjörð Bjarmason
2021-03-29 16:31   ` [PATCH 0/6] Makefile: make non-symlink & non-hardlink install sane Ævar Arnfjörð Bjarmason
2021-03-29 16:31     ` [PATCH 1/6] Makefile: symlink the same way under "symlinks" and "no hardlinks" Ævar Arnfjörð Bjarmason
2021-03-29 22:17       ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 2/6] Makefile: begin refactoring out "ln || ln -s || cp" pattern Ævar Arnfjörð Bjarmason
2021-03-29 22:20       ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 3/6] Makefile: refactor " Ævar Arnfjörð Bjarmason
2021-03-29 22:24       ` Junio C Hamano
2021-03-30 15:20         ` Jeff King
2021-03-30 18:36           ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 4/6] Makefile: make INSTALL_SYMLINKS affect the build directory Ævar Arnfjörð Bjarmason
2021-03-29 22:31       ` Junio C Hamano
2021-03-31 14:04         ` Ævar Arnfjörð Bjarmason
2021-03-29 16:31     ` [PATCH 5/6] Makefile: use "ln -f" instead of "rm && ln" Ævar Arnfjörð Bjarmason
2021-03-29 22:46       ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 6/6] Makefile: add a INSTALL_FALLBACK_LN_CP mode Ævar Arnfjörð Bjarmason
2021-03-29 22:53       ` Junio C Hamano
2021-03-31 14:03         ` Ævar Arnfjörð Bjarmason
2021-03-31 18:45           ` Junio C Hamano
2021-03-31 19:01             ` Ævar Arnfjörð Bjarmason
2021-03-29 23:08     ` [PATCH 0/6] Makefile: make non-symlink & non-hardlink install sane Junio C Hamano

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