git.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>,
	Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org,
	Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Subject: Re: [PATCH 1/1] vreportf(): avoid buffered write in favor of unbuffered one
Date: Tue, 29 Oct 2019 15:13:39 +0100 (CET)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.1910291510330.46@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <20191029134932.GA2843@sigill.intra.peff.net>

Hi Peff,

On Tue, 29 Oct 2019, Jeff King wrote:

> On Tue, Oct 29, 2019 at 01:30:51PM +0100, Johannes Schindelin wrote:
>
> > > Also, this is only to help output from us that goes via vreportf() and
> > > other codepaths in us that use stdio to write to the standard error
> > > stream can still get mixed on Windows (I think the answer is yes,
> > > because we wouldn't need fflush() in this patch if we are covering all
> > > writes to the standard error stream)?
> >
> > Yes, `write()` can get interrupted, so there is still a slight chance of
> > interleaving.
> >
> > However, with `fprintf()`, apparently the MSVC runtime essentially
> > writes and flushes one character at a time, which will make it _much_
> > more likely that two competing processes write interleaved messages to
> > `stderr`.
>
> Wow, they have truly taken "unbuffered" to a whole new level.
>
> I don't mind seeing this for all platforms, though. I can't think of any
> downside, and having one less moving part to contend with in our
> error-reporting code seems like a good thing.
>
> > > > -	vsnprintf(msg, sizeof(msg), err, params);
> > > > +	size_t off = strlcpy(msg, prefix, sizeof(msg));
> > >
> > > Like snprintf(3) the strlcpy() and strlcat() functions return the
> > > total length of the string they tried to create.  For strlcpy() that
> > > means the length of src.
> >
> > True (I misread `compat/strlcpy.c` and forgot to consult the
> > documentation). This length can be longer than `msg`, of course.
>
> I'd recommend xsnprintf() here. If we have a prefix longer than our
> vreportf() buffer, I think a BUG() is the right outcome.

But BUG_fl() calls vreportf(). I am worried about an infinite
recursion...

>
> > I `git grep`ed and saw that only very short `prefix`es are hard-coded.
> > So that is a hypothetical concern.
> >
> > However, Alex also indicated his discomfort with this, so I will change
> > the code to account for a `prefix` that is too long (the entire error
> > message will be clipped away in that case, which is unfortunate, but to
> > be expected).
>
> I'd disagree here. Any caller sending an arbitrarily-large prefix is
> holding it wrong, and we'd probably want to know as soon as possible
> (and a BUG() is our best bet there).

How about truncating already inside the prefix, then? It would miss the
entire error message... but at least it would print _something_...

Ciao,
Dscho

  reply	other threads:[~2019-10-29 14:13 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-28 15:00 [PATCH 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-28 15:00 ` [PATCH 1/1] vreportf(): avoid buffered write in favor of unbuffered one Johannes Schindelin via GitGitGadget
2019-10-29  3:18   ` Junio C Hamano
2019-10-29 12:30     ` Johannes Schindelin
2019-10-29 13:49       ` Jeff King
2019-10-29 14:13         ` Johannes Schindelin [this message]
2019-10-29 14:32           ` Jeff King
2019-10-29 20:09             ` Johannes Schindelin
2019-10-30  1:43               ` Junio C Hamano
2019-10-29 16:44         ` Junio C Hamano
2019-10-29 10:38   ` SZEDER Gábor
2019-10-29 12:38     ` Johannes Schindelin
2019-10-29 13:52       ` Jeff King
2019-10-29 14:18         ` Johannes Schindelin
2019-10-29 13:37 ` [PATCH v2 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-29 13:37   ` [PATCH v2 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget
2019-10-29 14:21     ` Alexandr Miloslavskiy
2019-10-29 19:57       ` Johannes Schindelin
2019-10-29 20:09         ` Jeff King
2019-10-29 20:24           ` Alexandr Miloslavskiy
2019-10-29 20:11         ` Alexandr Miloslavskiy
2019-10-29 20:01   ` [PATCH v3 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-29 20:01     ` [PATCH v3 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget
2019-10-29 20:32       ` Jeff King
2019-10-30  8:54         ` Johannes Schindelin
2019-10-31  6:24           ` Jeff King
2019-10-31 10:26             ` Johannes Schindelin
2019-10-31 15:48               ` Jeff King
2019-11-01 18:41                 ` Johannes Schindelin
2019-10-30  2:01       ` Junio C Hamano
2019-10-30  9:13         ` Johannes Schindelin
2019-10-30 10:44     ` [PATCH v4 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-30 10:44       ` [PATCH v4 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget
2019-11-02  4:05         ` 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

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=nycvar.QRO.7.76.6.1910291510330.46@tvgsbejvaqbjf.bet \
    --to=johannes.schindelin@gmx.de \
    --cc=alexandr.miloslavskiy@syntevo.com \
    --cc=git@vger.kernel.org \
    --cc=gitgitgadget@gmail.com \
    --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.
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 NNTP newsgroup(s).