Re: [PATCH] clean: explicitly `fflush` stdout

From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Jeff King <peff@peff.net>
Cc: "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>,
	git@vger.kernel.org, 마누엘 <nalla@hamal.uberspace.de>
Subject: Re: [PATCH] clean: explicitly `fflush` stdout
Date: Fri, 10 Apr 2020 16:03:26 +0200 (CEST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.2004101602330.46@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <20200408201454.GB2270445@coredump.intra.peff.net>

Hi Peff,

On Wed, 8 Apr 2020, Jeff King wrote:

> On Wed, Apr 08, 2020 at 07:33:00PM +0000, Johannes Schindelin via GitGitGadget wrote:
>
> > From: =?UTF-8?q?=EB=A7=88=EB=88=84=EC=97=98?= <nalla@hamal.uberspace.de>
> >
> > For performance reasons `stdout` is buffered by default. That leads to
> > problems if after printing to `stdout` a read on `stdin` is performed.
>
> This first paragraph left me scratching my head. It's only a problem for
> interactive uses, right? Would:
>
>   This can lead to problems for interactive commands which write a
>   prompt to `stdout` and then read user input on `stdin`. If the prompt
>   is left in the buffer, the user will not realize the program is
>   waiting for their input.
>
> make sense?

Thank you, yes, that makes sense.

Based on another suggestion of yours, I did refactor the code a bit more
and already sent out the result as v2.

Thank you,
Dscho

>
> > For that reason interactive commands like `git clean -i` do not function
> > properly anymore if the `stdout` is not flushed by `fflush(stdout)` before
> > trying to read from `stdin`.
>
> I'm not sure I understand this "anymore". Did the buffering change at
> some point, introducing a regression?
>
> > So let's precede all reads on `stdin` in `git clean -i` by flushing
> > `stdout`.
>
> This (and the patch) make sense to me. It might be worth factoring out a
> "read input from user" function and putting the flush there, but with
> only three affected call sites, I'm OK with it either way.
>
> >     This is yet another patch that was funneled through a Git for Windows
> >     PR. It has served us well for almost five years now, and it is beyond
> >     time that it find its final home in core Git.
>
> Agreed. I guess it didn't affect people on other platforms much because
> stdout to a terminal is generally line-buffered on POSIX systems. But
> it's better not to rely on that, plus it could create confusion if
> somebody tried to manipulate the interactive operation through a pipe
> (e.g., driving it from a GUI or something).
>
> -Peff
>