Re: [PATCH 7/9] strbuf_getwholeline: use getdelim if it is available

From: Eric Sunshine <sunshine@sunshineco.com>
To: Jeff King <peff@peff.net>
Cc: "Git List" <git@vger.kernel.org>, "René Scharfe" <l.s.r@web.de>,
	"Rasmus Villemoes" <rv@rasmusvillemoes.dk>
Subject: Re: [PATCH 7/9] strbuf_getwholeline: use getdelim if it is available
Date: Fri, 17 Apr 2015 06:16:48 -0400	[thread overview]
Message-ID: <CAPig+cSKtMPQGxp1Y2GinVRh2y--QyJh_nxhDez2CGFPP6B=xg@mail.gmail.com> (raw)
In-Reply-To: <20150416090138.GG17938@peff.net>

On Thu, Apr 16, 2015 at 5:01 AM, Jeff King <peff@peff.net> wrote:
> We spend a lot of time in strbuf_getwholeline in a tight
> loop reading characters from a stdio handle into a buffer.
> The libc getdelim() function can do this for us with less
> overhead. It's in POSIX.1-2008, and was a GNU extension
> before that. Therefore we can't rely on it, but can fall
> back to the existing getc loop when it is not available.
>
> The HAVE_GETDELIM knob is turned on automatically for Linux,
> where we have glibc. We don't need to set any new
> feature-test macros, because we already define _GNU_SOURCE.
> Other systems that implement getdelim may need to other
> macros (probably _POSIX_C_SOURCE >= 200809L), but we can
> address that along with setting the Makefile knob after
> testing the feature on those systems.
> [...]
>
> Based on a patch from Rasmus Villemoes <rv@rasmusvillemoes.dk>.
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> If somebody has a FreeBSD or OS X system to test on, I'd
> love to see what is needed to compile with HAVE_GETDELIM
> there.

Modern Mac OS X, 10.10.x Yosemite, has getdelim() and git builds fine
with HAVE_GETDELIM. I also tested on old Snow Leopard 10.5.8 from
2009. It does not have getdelim(). Unfortunately, I haven't been able
to determine when getdelim() was introduced on the Mac OS X, thus have
been unable to craft a simple rule for config.mak.uname.

> And to confirm that the performance is much better.
> Sharing my 1.6GB packed-refs file would be hard, but you
> should be able to generate something large and ridiculous.
> I'll leave that as an exercise to the reader.
>
> diff --git a/Makefile b/Makefile
> index 5f3987f..36655d5 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -359,6 +359,8 @@ all::
>  # compiler is detected to support it.
>  #
>  # Define HAVE_BSD_SYSCTL if your platform has a BSD-compatible sysctl function.
> +#
> +# Define HAVE_GETDELIM if your system has the getdelim() function.
>
>  GIT-VERSION-FILE: FORCE
>         @$(SHELL_PATH) ./GIT-VERSION-GEN
> @@ -1437,6 +1439,10 @@ ifdef HAVE_BSD_SYSCTL
>         BASIC_CFLAGS += -DHAVE_BSD_SYSCTL
>  endif
>
> +ifdef HAVE_GETDELIM
> +       BASIC_CFLAGS += -DHAVE_GETDELIM
> +endif
> +
>  ifeq ($(TCLTK_PATH),)
>  NO_TCLTK = NoThanks
>  endif
> diff --git a/config.mak.uname b/config.mak.uname
> index f4e77cb..d26665f 100644
> --- a/config.mak.uname
> +++ b/config.mak.uname
> @@ -36,6 +36,7 @@ ifeq ($(uname_S),Linux)
>         HAVE_DEV_TTY = YesPlease
>         HAVE_CLOCK_GETTIME = YesPlease
>         HAVE_CLOCK_MONOTONIC = YesPlease
> +       HAVE_GETDELIM = YesPlease
>  endif
>  ifeq ($(uname_S),GNU/kFreeBSD)
>         HAVE_ALLOCA_H = YesPlease