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@xxxxxxxxxxxxxxxxxx>.
Signed-off-by: Jeff King <peff@xxxxxxxx>
---
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. 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.
Makefile | 6 ++++++
config.mak.uname | 1 +
strbuf.c | 42 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 49 insertions(+)
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
diff --git a/strbuf.c b/strbuf.c
index 921619e..0d4f4e5 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -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)
{
--
2.4.0.rc2.384.g7297a4a
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html