Re: [PATCH 1/3] pack-write: use more idiomatic strbuf usage for packname construction

On Tue, Sep 07 2021, Taylor Blau wrote:

On Tue, Sep 07, 2021 at 09:42:36PM +0200, Ævar Arnfjörð Bjarmason wrote:

quoted

Change code added in 5889271114a (finish_tmp_packfile():use strbuf for

s/Change code/Code/ ?

That would make it:

    Change code added in X (...) to do strbuf_reset() instead...

Instead of:

    Code added in X (...) to do strbuf_reset() instead...

(I wondered also if the missing space in 5889271114a's subject line was
intentional, but it does appear in the original commit.)

*Nod*, it was automatically generated.

Reading this patch, I'm not sure I agree that this makes the later
changes any easier. To be honest, replacing things like

quoted

 	if (rev_tmp_name) {
-		strbuf_addf(name_buffer, "%s.rev", hash_to_hex(hash));
-		if (rename(rev_tmp_name, name_buffer->buf))
+		strbuf_addf(&sb, "%s%s.rev", tmp_basename->buf,
+			    hash_to_hex(hash));
+		if (rename(rev_tmp_name, sb.buf))
 			die_errno("unable to rename temporary reverse-index file");
-
-		strbuf_setlen(name_buffer, basename_len);
+		strbuf_reset(&sb);

Does not much help or hurt the readability, at least in my opinion. One
advantage of the pre-image is that we're doing less copying, but that's
probably splitting hairs at this point.

So, I would probably be just as happy without this patch. You mentioned
that it makes the later changes easier, but I couldn't come up with why.
I may be missing something, in which case it may be helpful to know what
that is and how it makes this change necessary.

It's not that continually appending/trimming the strbuf is per-se less
readable than having a "prefix" and copying/appending to it, and as you
point out this moves us towards more allocations, but in this case
that's not the bottleneck.

It's that if I retain the current pattern while splitting up these
functions I'd need to pass a "basename_len" owned by the caller between
the two, and we'd end up juggling the "tmpname" as the "if
(write_bitmap_index)" codepath is moved around.

So just having each site get the prefix and add its own suffix seemed
much easier to deal with,.