Subject: [PATCH] [GSOC] ref-filter: get rid of show_ref_array_item

From: "ZheNing Hu via GitGitGadget" <[email-masked]>
Date: Fri, 09 Apr 2021 13:35:47 +0000

From: ZheNing Hu <[email-masked]>

When we use `git for-each-ref`, every ref will call
`show_ref_array_item()` and allocate its own final strbuf.
But we can reuse the final strbuf for each step ref's output.
Since `show_ref_array_item()` is not used in many places,
we can directly delete `show_ref_array_item()` and use the
same logic code to replace it. In this way, the caller can
clearly see how the loop work.

The performance for `git for-each-ref` on the Git repository
itself with performance testing tool `hyperfine` changes from
23.7 ms ± 0.9 ms to 22.2 ms ± 1.0 ms.

At the same time, we apply this optimization to `git tag -l`
and `git branch -l`, the `git branch -l` performance upgrade
from 5.8 ms ± 0.8 ms to 2.7 ms ± 0.2 ms and `git tag -l`
performance upgrade from 5.9 ms ± 0.4 ms to 5.4 ms ± 0.4 ms.
Since the number of tags in git.git is much more than branches,
so this shows that the optimization will be more obvious in
those repositories that contain a small number of objects.

This approach is similar to the one used by 79ed0a5
(cat-file: use a single strbuf for all output, 2018-08-14)
to speed up the cat-file builtin.

Signed-off-by: ZheNing Hu <[email-masked]>
---
    [GSOC] ref-filter: get rid of show_ref_array_item
    
    Now git for-each-ref can reuse final buf for all refs output, the
    performance is slightly improved, This optimization is also applied to
    git tag -l and git branch -l.
    
    Thanks.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-928%2Fadlternative%2Fref-filter-reuse-buf-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-928/adlternative/ref-filter-reuse-buf-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/928

 builtin/branch.c       |  8 ++++----
 builtin/for-each-ref.c | 13 +++++++++++--
 builtin/tag.c          | 13 +++++++++++--
 ref-filter.c           | 24 +++++++++---------------
 ref-filter.h           |  2 --
 5 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index bcc00bcf182d..5c797e992aa4 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -411,6 +411,8 @@ static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sortin
 {
 	int i;
 	struct ref_array array;
+	struct strbuf out = STRBUF_INIT;
+	struct strbuf err = STRBUF_INIT;
 	int maxwidth = 0;
 	const char *remote_prefix = "";
 	char *to_free = NULL;
@@ -440,8 +442,7 @@ static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sortin
 	ref_array_sort(sorting, &array);
 
 	for (i = 0; i < array.nr; i++) {
-		struct strbuf out = STRBUF_INIT;
-		struct strbuf err = STRBUF_INIT;
+		strbuf_reset(&out);
 		if (format_ref_array_item(array.items[i], format, &out, &err))
 			die("%s", err.buf);
 		if (column_active(colopts)) {
@@ -452,10 +453,9 @@ static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sortin
 			fwrite(out.buf, 1, out.len, stdout);
 			putchar('\n');
 		}
-		strbuf_release(&err);
-		strbuf_release(&out);
 	}
 
+	strbuf_release(&out);
 	ref_array_clear(&array);
 	free(to_free);
 }
diff --git a/builtin/for-each-ref.c b/builtin/for-each-ref.c
index cb9c81a04606..157cc8623949 100644
--- a/builtin/for-each-ref.c
+++ b/builtin/for-each-ref.c
@@ -22,6 +22,8 @@ int cmd_for_each_ref(int argc, const char **argv, const char *prefix)
 	struct ref_array array;
 	struct ref_filter filter;
 	struct ref_format format = REF_FORMAT_INIT;
+	struct strbuf output = STRBUF_INIT;
+	struct strbuf err = STRBUF_INIT;
 
 	struct option opts[] = {
 		OPT_BIT('s', "shell", &format.quote_style,
@@ -80,8 +82,15 @@ int cmd_for_each_ref(int argc, const char **argv, const char *prefix)
 
 	if (!maxcount || array.nr < maxcount)
 		maxcount = array.nr;
-	for (i = 0; i < maxcount; i++)
-		show_ref_array_item(array.items[i], &format);
+	for (i = 0; i < maxcount; i++) {
+		strbuf_reset(&output);
+		if (format_ref_array_item(array.items[i], &format, &output, &err))
+			die("%s", err.buf);
+		fwrite(output.buf, 1, output.len, stdout);
+		putchar('\n');
+	}
+
+	strbuf_release(&output);
 	ref_array_clear(&array);
 	return 0;
 }
diff --git a/builtin/tag.c b/builtin/tag.c
index d403417b5625..b172f3861413 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -39,6 +39,8 @@ static int list_tags(struct ref_filter *filter, struct ref_sorting *sorting,
 		     struct ref_format *format)
 {
 	struct ref_array array;
+	struct strbuf output = STRBUF_INIT;
+	struct strbuf err = STRBUF_INIT;
 	char *to_free = NULL;
 	int i;
 
@@ -63,8 +65,15 @@ static int list_tags(struct ref_filter *filter, struct ref_sorting *sorting,
 	filter_refs(&array, filter, FILTER_REFS_TAGS);
 	ref_array_sort(sorting, &array);
 
-	for (i = 0; i < array.nr; i++)
-		show_ref_array_item(array.items[i], format);
+	for (i = 0; i < array.nr; i++) {
+		strbuf_reset(&output);
+		if (format_ref_array_item(array.items[i], format, &output, &err))
+			die("%s", err.buf);
+		fwrite(output.buf, 1, output.len, stdout);
+		putchar('\n');
+	}
+
+	strbuf_release(&output);
 	ref_array_clear(&array);
 	free(to_free);
 
diff --git a/ref-filter.c b/ref-filter.c
index f0bd32f71416..9e38e42fb7ae 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -2435,27 +2435,21 @@ int format_ref_array_item(struct ref_array_item *info,
 	return 0;
 }
 
-void show_ref_array_item(struct ref_array_item *info,
-			 const struct ref_format *format)
-{
-	struct strbuf final_buf = STRBUF_INIT;
-	struct strbuf error_buf = STRBUF_INIT;
-
-	if (format_ref_array_item(info, format, &final_buf, &error_buf))
-		die("%s", error_buf.buf);
-	fwrite(final_buf.buf, 1, final_buf.len, stdout);
-	strbuf_release(&error_buf);
-	strbuf_release(&final_buf);
-	putchar('\n');
-}
-
 void pretty_print_ref(const char *name, const struct object_id *oid,
 		      const struct ref_format *format)
 {
 	struct ref_array_item *ref_item;
+	struct strbuf output = STRBUF_INIT;
+	struct strbuf err = STRBUF_INIT;
+
 	ref_item = new_ref_array_item(name, oid);
 	ref_item->kind = ref_kind_from_refname(name);
-	show_ref_array_item(ref_item, format);
+	if (format_ref_array_item(ref_item, format, &output, &err))
+		die("%s", err.buf);
+	fwrite(output.buf, 1, output.len, stdout);
+	putchar('\n');
+
+	strbuf_release(&output);
 	free_array_item(ref_item);
 }
 
diff --git a/ref-filter.h b/ref-filter.h
index 19ea4c413409..baf72a718965 100644
--- a/ref-filter.h
+++ b/ref-filter.h
@@ -119,8 +119,6 @@ int format_ref_array_item(struct ref_array_item *info,
 			  const struct ref_format *format,
 			  struct strbuf *final_buf,
 			  struct strbuf *error_buf);
-/*  Print the ref using the given format and quote_style */
-void show_ref_array_item(struct ref_array_item *info, const struct ref_format *format);
 /*  Parse a single sort specifier and add it to the list */
 void parse_ref_sorting(struct ref_sorting **sorting_tail, const char *atom);
 /*  Callback function for parsing the sort option */

base-commit: 2e36527f23b7f6ae15e6f21ac3b08bf3fed6ee48
-- 
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