Re: [PATCH] Makefile: add and use the ".DELETE_ON_ERROR" flag

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Jun 24, 2021, 13:53 UTC
Message-ID: <871r8r1hwe.fsf@evledraar.gmail.com>
In-Reply-To: <YNOz1GD/8+CaUvRz@coredump.intra.peff.net>

On Wed, Jun 23 2021, Jeff King wrote:

Show 19 quoted lines

> On Wed, Jun 23, 2021 at 09:54:06PM +0200, Ævar Arnfjörð Bjarmason wrote:
>
>> 
>> > Just to be clear, I would be happy to drop the "oops, the tests barf if
>> > you recompile halfway through" feature away if it made things more
>> > robust overall (i.e., if we always did an atomic rename-into-place). I
>> > just consider it the fact that we do clobber to be an accidental feature
>> > that is not really worth "fixing". But if we care about "oops, make was
>> > interrupted and now you have a stale build artifact with a bogus
>> > timestamp" type of robustness, and "the tests barf" goes away as a side
>> > effect, I won't complain.
>> 
>> ..and "this behavior is really annoying on one platform we target, and
>> the fix is rather trivial".
>
> Yeah, that's a fine reason, too. I'm not entirely clear on what the
> problem is, though, or why this is the best solution (I expect you
> probably explained it in an earlier thread/series, but if so it went in
> one ear and out the other on my end).

On *nix systems you can open a file, and unlink() it in another process, on Windows this is an error.

AIX has its own variant of this annoying behavior, you can't clobber (or open for writing) binaries that are currently being run, you can unlink and rename them though.

So without that "mv $@ $@+" trick you can't recompile if you have a concurrent test (that you don't care about failing) running, and we have bugs in our tests where e.g. "git-daemon" gets lost and won't get killed on that platform, so you can't recompile and test without tracking it down and killing it.