Re: [PATCH v2 08/24] midx: respect 'core.multiPackIndex' when writing

On Tue, Jul 27, 2021 at 01:42:35PM -0400, Jeff King wrote:

On Tue, Jul 27, 2021 at 01:36:34PM -0400, Taylor Blau wrote:

quoted

quoted

But now the internal midx writing code can never call close_midx() on
that, because it does not own it to close. Can we simply drop the
close_midx() call there?

This would all make much more sense to me if write_midx_internal()
simply took a conceptually read-only midx as a parameter, and the caller
passed in the appropriate one (probably even using
prepare_multi_pack_index_one() to get it).

No, we can't drop the close_midx() call there because we must close the
MIDX file on Windows before moving a new one into place. My feeling is
we should always be working on the r->objects->multi_pack_index pointer,
and calling close_object_store() there instead of close_midx().

Does that seem like a reasonable approach to you?

Yes, though I'd have said that it is the responsibility of the caller
(who knows we are operating with r->objects->multi_pack_index) to do
that closing. But maybe it's not possible if the rename-into-place
happens at too low a level.

Right; write_midx_internal() needs to access the MIDX right up until the
point that we write the new one into place, so the only place to close
it is in write_midx_internal().

BTW, yet another weirdness: close_object_store() will call close_midx()
on the outermost midx struct, ignoring o->multi_pack_index->next
entirely. So that's a leak, but also means we may not be closing the
midx we're interested in (since write_midx_internal() takes an
object-dir parameter, and we could be pointing to some other
object-dir's midx).

Yuck, this is a mess. I'm tempted to say that we should be closing the
MIDX that we're operating on inside of write_midx_internal() so we can
write, but then declaring the whole object store to be bunk and calling
close_object_store() before leaving the function. Of course, one of
those steps should be closing the inner-most MIDX before closing the
next one and so on.

-Peff

Thanks,
Taylor