Re: [PATCH 2/2] [GSOC] ref-filter: reuse output buffer

From: ZheNing Hu <adlternative@gmail.com>
Date: Apr 20, 2021, 06:05 UTC
Message-ID: <CAOLTT8SDv6bFOdqu6f_=QWPrQtbyFp_XYFkdRmONg4tJ7C=fAA@mail.gmail.com>
In-Reply-To: <xmqq7dky9ear.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> 于2021年4月20日周二 上午5:04写道：

Show 45 quoted lines

>
> "ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > diff --git a/builtin/branch.c b/builtin/branch.c
> > index bcc00bcf182d..00081de1aed8 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);
>
> This change relies on the fact that format_ref_array_item() will
> never touch error when it returns 0 (success); otherwise, we'd end
> up accumulating err from multiple calls to it in the loop until it
> returns non-zero (failure), at which point we emit a single "fatal:"
> prefix to show multiple error messages.  Which leans me ...
>
> > @@ -452,10 +453,10 @@ 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(&err);
> > +     strbuf_release(&out);
>
> ... to suspect that the _release() of err will always be a no-op.
>

Yes, it's a no-op to _release(&err) In the present situation.

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> It may be easier to follow if err is _reset() always where out is
> _reset(), from code cleanliness's perspective.  Then nobody has to
> wonder why we do not reset err inside loop even though we release
> at the end.
>
> It also is OK to document more clearly that we assume that the loop
> will not exit without calling die() when err is not empty.  If we
> take that route, we may want to drop _release(&err) at the end.
>
> I do not know which of the two is better, but the code presented
> which is halfway between these two does not quite look easy to
> reason about.
>

René Scharfe mention that it make leaks checking harder if we without releasing this err. So on balance, adding err's _reset() in the loop seems like a viable option. The change in performance will also be minimal too.

Even though we're using _release() in the loop in v1, and then Peff think that we don't need to _release() err, but code cleanness wasn't a concern at the time.

So I'll add _reset() to the loop in the next iteration.

> Thanks.
>

Thanks. -- ZheNing Hu