From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Michael Haggerty <mhagger@alum.mit.edu>,
William Duclot <william.duclot@ensimag.grenoble-inp.fr>,
git@vger.kernel.org, antoine.queru@ensimag.grenoble-inp.fr,
francois.beutin@ensimag.grenoble-inp.fr,
Johannes.Schindelin@gmx.de, mh@glandium.org
Subject: Re: [PATCH V2 3/3] strbuf: allow to use preallocated memory
Date: Wed, 8 Jun 2016 15:52:48 -0400 [thread overview]
Message-ID: <20160608195248.GA4264@sigill.intra.peff.net> (raw)
In-Reply-To: <xmqq37onlawb.fsf@gitster.mtv.corp.google.com>
On Wed, Jun 08, 2016 at 12:48:36PM -0700, Junio C Hamano wrote:
> Jeff King <peff@peff.net> writes:
>
> > That made me wonder if we could repeatedly reuse a buffer attached to
> > the file descriptor. And indeed, isn't that what stdio is? The whole
> > reason this buffer exists is because we are using a direct descriptor
> > write. If we switched this function to use fprintf(), we'd avoid the
> > whole buffer question, have a fixed cap on our memory use (since we just
> > flush anytime the buffer is full) _and_ we'd reduce the number of
> > write syscalls we're making by almost a factor of 100.
>
> The primary reason why we avoid stdio in the lower level part of I/O
> is that the error reporting and handling is horrible.
>
> e.g. c.f. http://article.gmane.org/gmane.comp.version-control.git/27019
>
> Otherwise, I'd agree with your "Why aren't we using stdio if
> counting and avoiding overflow is so hard?".
I agree it can be confusing (especially on the output side your errors
are likely deferred until the next flush). But in this particular case,
I think it's an improvement (see the patch I just sent and its
discussion of error handling).
I also think we could smooth over the rough edges by wrapping the
complexity (we already have fprintf_or_die, which arguably could be used
in this case, but I went with the solution that stayed closer to what
the original code was doing). And if stdio is truly too horrible, I'd
suggest we implement our own buffered I/O. Because that's effectively
what such call-sites are doing, but in a really ad-hoc and
non-performant way.
-Peff
next prev parent reply other threads:[~2016-06-08 19:53 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-06 15:13 [PATCH V2 0/3] strbuf: improve API William Duclot
2016-06-06 15:13 ` [PATCH V2 1/3] strbuf: add tests William Duclot
2016-06-06 16:11 ` Matthieu Moy
2016-06-07 8:44 ` Johannes Schindelin
2016-06-06 15:13 ` [PATCH V2 2/3] pretty.c: rename strbuf_wrap() function William Duclot
2016-06-06 16:12 ` Matthieu Moy
2016-06-07 9:04 ` Johannes Schindelin
2016-06-06 15:13 ` [PATCH V2 3/3] strbuf: allow to use preallocated memory William Duclot
2016-06-06 16:17 ` Matthieu Moy
2016-06-06 17:19 ` Junio C Hamano
2016-06-06 20:39 ` William Duclot
2016-06-06 22:44 ` Junio C Hamano
2016-06-06 22:58 ` Jeff King
2016-06-06 23:24 ` Junio C Hamano
2016-06-06 23:25 ` Junio C Hamano
2016-06-06 23:30 ` Jeff King
2016-06-07 9:06 ` William Duclot
2016-06-07 18:10 ` Junio C Hamano
2016-06-08 16:20 ` Michael Haggerty
2016-06-08 18:07 ` Junio C Hamano
2016-06-08 19:19 ` Jeff King
2016-06-08 19:42 ` [PATCH] send-pack: use buffered I/O to talk to pack-objects Jeff King
2016-06-09 12:10 ` Matthieu Moy
2016-06-09 14:34 ` Ramsay Jones
2016-06-09 17:12 ` Jeff King
2016-06-09 22:40 ` Ramsay Jones
2016-06-09 16:40 ` Junio C Hamano
2016-06-09 17:14 ` Jeff King
2016-06-09 17:22 ` Matthieu Moy
2016-06-08 19:48 ` [PATCH V2 3/3] strbuf: allow to use preallocated memory Junio C Hamano
2016-06-08 19:52 ` Jeff King [this message]
2016-06-08 23:05 ` Junio C Hamano
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