Commit 0cc30e0e authored by Jeff King's avatar Jeff King Committed by Junio C Hamano

strbuf_getwholeline: use getdelim if it is available

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.

Running "git rev-parse refs/heads/does-not-exist" on a repo
with an extremely large (1.6GB) packed-refs file went from
(best-of-5):

  real    0m8.601s
  user    0m8.084s
  sys     0m0.524s

to:

  real    0m6.768s
  user    0m6.340s
  sys     0m0.432s

for a wall-clock speedup of 21%.

Based on a patch from Rasmus Villemoes <rv@rasmusvillemoes.dk>.
Signed-off-by: default avatarJeff King <peff@peff.net>
Signed-off-by: default avatarJunio C Hamano <gitster@pobox.com>
parent f80c153b
......@@ -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
......
......@@ -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
......
......@@ -435,6 +435,47 @@ int strbuf_getcwd(struct strbuf *sb)
return -1;
}
#ifdef HAVE_GETDELIM
int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
{
ssize_t r;
if (feof(fp))
return EOF;
strbuf_reset(sb);
/* Translate slopbuf to NULL, as we cannot call realloc on it */
if (!sb->alloc)
sb->buf = NULL;
r = getdelim(&sb->buf, &sb->alloc, term, fp);
if (r > 0) {
sb->len = r;
return 0;
}
assert(r == -1);
/*
* Normally we would have called xrealloc, which will try to free
* memory and recover. But we have no way to tell getdelim() to do so.
* Worse, we cannot try to recover ENOMEM ourselves, because we have
* no idea how many bytes were read by getdelim.
*
* Dying here is reasonable. It mirrors what xrealloc would do on
* catastrophic memory failure. We skip the opportunity to free pack
* memory and retry, but that's unlikely to help for a malloc small
* enough to hold a single line of input, anyway.
*/
if (errno == ENOMEM)
die("Out of memory, getdelim failed");
/* Restore slopbuf that we moved out of the way before */
if (!sb->buf)
strbuf_init(sb, 0);
return EOF;
}
#else
int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
{
int ch;
......@@ -458,6 +499,7 @@ int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
sb->buf[sb->len] = '\0';
return 0;
}
#endif
int strbuf_getline(struct strbuf *sb, FILE *fp, int term)
{
......
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