Re: [PATCH] strbuf_write: omit system call when length is zero

[Junio C Hamano <gitster@pobox.com>]

Duy Nguyen <pclouds@gmail.com> writes:

> On Fri, Feb 26, 2016 at 5:34 AM, Stefan Beller <sbeller@google.com> wrote:
>> In case the length of the buffer is zero, we do not need to call the
>> fwrite system call as a performance improvement.
>
> fwrite is a libc call, not system call. Are you sure it always calls
> write() (assuming buffering is off)?

I do not think so, but I suspect that the patch misstates its
rationale (I said I get uncomfortable every time I see a function
that takes size and nelem separately used by a caller that can
potentially pass nleme=0, when I wondered it it is OK that no caller
of this funtion checks its return value).


>
>>
>> Signed-off-by: Stefan Beller <sbeller@google.com>
>> ---
>>
>>  This applies on top of v17 for origin/sb/submodule-parallel-update.
>>
>>  In case there are other reasons for origin/sb/submodule-parallel-update
>>  to need a reroll I'll squash it in. But as this is a pure performance
>>  optimization in a case we are not running into with that series and that
>>  series is clashing with Davids refs backend series, I figure we may not
>>  want to have a reroll for this fix alone.
>>
>>  Thanks,
>>  Stefan
>>
>>
>>  strbuf.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/strbuf.c b/strbuf.c
>> index 71345cd..5f6da82 100644
>> --- a/strbuf.c
>> +++ b/strbuf.c
>> @@ -397,7 +397,7 @@ ssize_t strbuf_read_once(struct strbuf *sb, int fd, size_t hint)
>>
>>  ssize_t strbuf_write(struct strbuf *sb, FILE *f)
>>  {
>> -       return fwrite(sb->buf, 1, sb->len, f);
>> +       return sb->len ? fwrite(sb->buf, 1, sb->len, f) : 0;
>>  }
>>
>>
>> --
>> 2.7.2.374.ga5f0819.dirty
>>
>> --
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