@matheusbsbs / matheus-bagliano / commits / 0cc30e0e84

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: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Jeff King committed Apr 16, 2015 at 05:01 UTC 0cc30e0e842a25846e76e09f62a1d425a25ee556

3 files changed +49

Makefile

@@ -359,6 +359,8 @@ all::

359 # compiler is detected to support it.

360 #

361 # Define HAVE_BSD_SYSCTL if your platform has a BSD-compatible sysctl function.

362 +#

363 +# Define HAVE_GETDELIM if your system has the getdelim() function.

364

365 GIT-VERSION-FILE: FORCE

366 @$(SHELL_PATH) ./GIT-VERSION-GEN

@@ -1437,6 +1439,10 @@ ifdef HAVE_BSD_SYSCTL

1439 BASIC_CFLAGS += -DHAVE_BSD_SYSCTL

1440 endif

1441

1442 +ifdef HAVE_GETDELIM

1443 + BASIC_CFLAGS += -DHAVE_GETDELIM

1444 +endif

1445 +

1446 ifeq ($(TCLTK_PATH),)

1447 NO_TCLTK = NoThanks

1448 endif

config.mak.uname

@@ -36,6 +36,7 @@ ifeq ($(uname_S),Linux)

36 HAVE_DEV_TTY = YesPlease

37 HAVE_CLOCK_GETTIME = YesPlease

38 HAVE_CLOCK_MONOTONIC = YesPlease

39 + HAVE_GETDELIM = YesPlease

40 endif

41 ifeq ($(uname_S),GNU/kFreeBSD)

42 HAVE_ALLOCA_H = YesPlease

strbuf.c

+42

@@ -435,6 +435,47 @@ int strbuf_getcwd(struct strbuf *sb)

435 return -1;

436 }

437

438 +#ifdef HAVE_GETDELIM

439 +int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)

440 +{

441 + ssize_t r;

442 +

443 + if (feof(fp))

444 + return EOF;

445 +

446 + strbuf_reset(sb);

447 +

448 + /* Translate slopbuf to NULL, as we cannot call realloc on it */

449 + if (!sb->alloc)

450 + sb->buf = NULL;

451 + r = getdelim(&sb->buf, &sb->alloc, term, fp);

452 +

453 + if (r > 0) {

454 + sb->len = r;

455 + return 0;

456 + }

457 + assert(r == -1);

458 +

459 + /*

460 + * Normally we would have called xrealloc, which will try to free

461 + * memory and recover. But we have no way to tell getdelim() to do so.

462 + * Worse, we cannot try to recover ENOMEM ourselves, because we have

463 + * no idea how many bytes were read by getdelim.

464 + *

465 + * Dying here is reasonable. It mirrors what xrealloc would do on

466 + * catastrophic memory failure. We skip the opportunity to free pack

467 + * memory and retry, but that's unlikely to help for a malloc small

468 + * enough to hold a single line of input, anyway.

469 + */

470 + if (errno == ENOMEM)

471 + die("Out of memory, getdelim failed");

472 +

473 + /* Restore slopbuf that we moved out of the way before */

474 + if (!sb->buf)

475 + strbuf_init(sb, 0);

476 + return EOF;

477 +}

478 +#else

479 int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)

480 {

481 int ch;

@@ -458,6 +499,7 @@ int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)

499 sb->buf[sb->len] = '\0';

500 return 0;

501 }

502 +#endif

503

504 int strbuf_getline(struct strbuf *sb, FILE *fp, int term)

505 {