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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	git@vger.kernel.org,
	"Johannes Schindelin" <johannes.schindelin@gmx.de>,
	"Jonathan Nieder" <jrnieder@gmail.com>
Subject: Re: [PATCH v2 4/5] Makefile: add the ".DELETE_ON_ERROR" flag
Date: Wed, 31 Mar 2021 02:58:46 -0400	[thread overview]
Message-ID: <YGQdpkHAcFR/zNOx@coredump.intra.peff.net> (raw)
In-Reply-To: <xmqqft0cebft.fsf@gitster.g>

On Tue, Mar 30, 2021 at 11:36:06AM -0700, Junio C Hamano wrote:

> > Yes, I think it's fine to treat it as "nice if we have it, but OK
> > otherwise". But also, .DELETE_ON_ERROR first shows up in the GNU make
> > git repository in version 3.71.5 from 1994. So I think we can probably
> > just assume it's everywhere.
> 
> OK.  That raises my hopes up that we may be able to simplify things
> like this
> 
>     config-list.h:
>             $(QUIET_GEN)$(SHELL_PATH) ./generate-configlist.sh \
>                     >$@+ && mv $@+ $@
> 
> into
> 
>     config-list.h:
>             $(QUIET_GEN)$(SHELL_PATH) ./generate-configlist.sh >$@

Yes, I think .DELETE_ON_ERROR would accomplish roughly the same thing.
Though note that it's essentially a "rollback" strategy. We create the
broken file, realize there was an error, and the roll it back (as
opposed to the "mv" strategy, which confirms everything is good before
committing it into place). This is worse than a "commit" strategy in a
few ways:

  - somebody else may racily see the broken state. I'm not too concerned
    with this, and from the rest of the thread I don't think you are
    either.

  - we may be left in the broken state if the rollback fails. Plausible
    reasons are: somebody kills "make" (I'd hope on the obvious ^C that
    it catches the signal and deletes before exiting), bug in make,
    transient OS error, power failure, etc.

I don't know how paranoid we want to be about this, especially the
latter. My general inclination is to prefer "commit" systems as more
robust, but it is just a Makefile.

-Peff

  reply	other threads:[~2021-03-31  6:59 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
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 [this message]
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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