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

>
> From: ZheNing Hu <adlternative@gmail.com>
>
> 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 <adlternative@gmail.com>
> ---
>     [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
> --
> gitgitgadget