From: "Randall S. Becker" <rsbecker@nexbridge.com>
To: "'Jeff King'" <peff@peff.net>
Cc: "'Junio C Hamano'" <gitster@pobox.com>, <git@vger.kernel.org>,
<git-packagers@googlegroups.com>
Subject: RE: [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop
Date: Tue, 30 Jul 2019 16:25:56 -0400 [thread overview]
Message-ID: <04b201d54715$0180a0f0$0481e2d0$@nexbridge.com> (raw)
In-Reply-To: <20190730194515.GA1088@sigill.intra.peff.net>
On July 30, 2019 3:45 PM, Jeff King wrote:
> To: Randall S. Becker <rsbecker@nexbridge.com>
> Cc: 'Junio C Hamano' <gitster@pobox.com>; git@vger.kernel.org; git-
> packagers@googlegroups.com
> Subject: Re: [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop
>
> On Tue, Jul 30, 2019 at 01:08:37PM -0400, Randall S. Becker wrote:
>
> > t0016: oidmap
> >
> > Subtest 6 had an ordering issue. We do not know whether the problem is
> the code or the test result not keeping up with the code changes.
> > --- expect 2019-07-30 16:56:36 +0000
> > +++ actual 2019-07-30 16:56:36 +0000
> > @@ -1,6 +1,6 @@
> > NULL
> > NULL
> > NULL
> > +7c7cd714e262561f73f3079dfca4e8724682ac21 3
> > 139b20d8e6c5b496de61f033f642d0e3dbff528d 2
> > d79ce1670bdcb76e6d1da2ae095e890ccb326ae9 1
> > -7c7cd714e262561f73f3079dfca4e8724682ac21 3
>
> This one is very curious. It's iterating a hash, which _seems_ like it would
> produce non-deterministic output. But neither this test nor the hashmap test
> it is based on sorts the output, and they pass consistently for me. I assume
> that's because while hash ordering is not guaranteed, it happens to be the
> same as long the pattern of inserts is the same (with our implementation,
> which does not do any hash randomization).
>
> But I am scratching my head as to what could be different on your platform
> that would cause a different ordering (especially when the hashmap test this
> is based on doesn't get one!).
>
> I guess in some sense it may not be worth tracking down, and we should just
> sort the output of a hash iteration unconditionally when comparing it to
> expected output.
Definitely a head scratcher. Is it possible that the bucket() function, which uses
key->hash & (map->tablesize - 1);
might better use
key->hash % (map->tablesize - 1);
I have not seen a bucket computation done this way before so that surprised me, not that it should make a difference on hash-determinism. The only thing that might is an uninitialized stack variable, which on this platform's C compiler will not initialize. Global statics are always 0 unless otherwise specified, but I'm not sure about stack-local (but there's nothing wrong I can see in hashmap.c on those points.
Sorting the output seems like a safe option, providing that the hash is itself demonstrably solid otherwise.
Cheers,
Randall
next prev parent reply other threads:[~2019-07-30 20:26 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-30 17:08 [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop Randall S. Becker
2019-07-30 17:31 ` Junio C Hamano
2019-07-30 18:09 ` Matheus Tavares Bernardino
2019-07-30 18:10 ` Randall S. Becker
2019-07-30 18:35 ` Junio C Hamano
2019-07-30 19:45 ` Jeff King
2019-07-30 20:25 ` Randall S. Becker [this message]
2019-07-30 19:49 ` Todd Zullinger
2019-07-30 20:02 ` Jeff King
2019-07-30 20:39 ` Junio C Hamano
2019-07-30 20:56 ` SZEDER Gábor
2019-07-31 0:59 ` Jeff King
2019-07-31 1:23 ` Jeff King
2019-07-31 1:27 ` Jeff King
2019-07-31 1:59 ` Todd Zullinger
2019-07-31 3:27 ` Jeff King
2019-07-31 3:53 ` Jeff King
2019-07-31 17:17 ` Junio C Hamano
2019-07-31 21:22 ` non-cryptographic hash algorithms in git Jeff King
2019-07-31 4:06 ` [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop René Scharfe
2019-07-31 4:30 ` Jeff King
2019-07-31 6:04 ` Todd Zullinger
2019-07-31 16:57 ` Junio C Hamano
2019-07-30 20:27 ` Randall S. Becker
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='04b201d54715$0180a0f0$0481e2d0$@nexbridge.com' \
--to=rsbecker@nexbridge.com \
--cc=git-packagers@googlegroups.com \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=peff@peff.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).