From: Stefan Beller <sbeller@google.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Johannes Sixt <j6t@kdbg.org>,
"git@vger.kernel.org" <git@vger.kernel.org>,
Brandon Williams <bmwill@google.com>
Subject: Re: [PATCHv2] attr: convert to new threadsafe API
Date: Wed, 12 Oct 2016 14:42:37 -0700 [thread overview]
Message-ID: <CAGZ79kb-xKDNG-LC56i8Y-FAaYZwr8zzXuC9snj1PavnQ6cdCA@mail.gmail.com> (raw)
In-Reply-To: <xmqq8ttt2qpp.fsf@gitster.mtv.corp.google.com>
On Wed, Oct 12, 2016 at 2:38 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Johannes Sixt <j6t@kdbg.org> writes:
>
>> Sigh. DCLP, the Double Checked Locking Pattern. ...
>> I suggest you go without it, then measure, and only *then* optimize if
>> it is a bottleneck.
>
> That comes from me in earlier discussion before the patch, namely in
> <xmqqeg3m8y6y.fsf@gitster.mtv.corp.google.com>, where I wondered if
> a cheap check outside the lock may be a possible optimization
> opportunity, as this is a classic singleton that will not be
> deinitialized, and once the codepath gets exercised, we would be
> taking the "nothing to do" route 100% of the time.
>
Having followed that advice (and internally having a DCLP), I think
we have Triple Checked Locking Pattern in this patch. Nobody wrote
a paper on how that would not work, yet. ;)
In the reroll I plan to reduce it to a Single Checked (inside a mutex)
Locking Pattern, though I would expect that performance (or lack thereof)
will show then. But let's postpone measuring until we have a working patch.
next prev parent reply other threads:[~2016-10-12 21:42 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-11 23:59 [PATCHv2] attr: convert to new threadsafe API Stefan Beller
2016-10-12 6:12 ` Junio C Hamano
2016-10-12 6:51 ` Stefan Beller
2016-10-12 16:20 ` Junio C Hamano
2016-10-12 20:02 ` Stefan Beller
2016-10-12 20:59 ` Junio C Hamano
2016-10-12 22:57 ` Junio C Hamano
2016-10-12 20:07 ` Johannes Sixt
2016-10-12 21:38 ` Junio C Hamano
2016-10-12 21:42 ` Stefan Beller [this message]
2016-10-12 21:50 ` Junio C Hamano
2016-10-12 21:45 ` Jacob Keller
2016-10-12 21:47 ` Stefan Beller
2016-10-12 21:28 ` Junio C Hamano
2016-10-12 21:39 ` Stefan Beller
2016-10-12 21:44 ` Junio C Hamano
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=CAGZ79kb-xKDNG-LC56i8Y-FAaYZwr8zzXuC9snj1PavnQ6cdCA@mail.gmail.com \
--to=sbeller@google.com \
--cc=bmwill@google.com \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=j6t@kdbg.org \
/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).