Subject: Re: [PATCH v2 09/16] packfile: split up responsibilities of `reprepare_packed_git()`

From: Taylor Blau <[email-masked]>
Date: Mon, 25 Aug 2025 22:10:02 -0400

On Thu, Aug 21, 2025 at 09:39:07AM +0200, Patrick Steinhardt wrote:
> While the logic is hosted in "packfile.c", it clearly reaches into other
> subsystems that aren't related to packfiles.
>
> Split up the responsibility and introduce `odb_reprepare()` which now
> becomes responsible for repreparing the whole object database. The
> existing `reprepare_packed_git()` function is refactored accordingly and
> only cares about reloading the packfile store now.

Makes sense.

> diff --git a/odb.c b/odb.c
> index 80ec6fc1fa..37ed21f53b 100644
> --- a/odb.c
> +++ b/odb.c
> @@ -694,7 +694,7 @@ static int do_oid_object_info_extended(struct object_database *odb,
>
>  		/* Not a loose object; someone else may have just packed it. */
>  		if (!(flags & OBJECT_INFO_QUICK)) {
> -			reprepare_packed_git(odb->repo);
> +			odb_reprepare(odb->repo->objects);
>  			if (find_pack_entry(odb->repo, real, &e))
>  				break;
>  		}
> @@ -1039,3 +1039,26 @@ void odb_clear(struct object_database *o)
>
>  	string_list_clear(&o->submodule_source_paths, 0);
>  }
> +
> +void odb_reprepare(struct object_database *o)

OK; so here is the new location for the non-packfile related portions of
the former reprepare_packed_git() function. That makes sense, but...

> +{
> +	struct odb_source *source;
> +
> +	/*
> +	 * Reprepare alt odbs, in case the alternates file was modified
> +	 * during the course of this process. This only _adds_ odbs to
> +	 * the linked list, so existing odbs will continue to exist for
> +	 * the lifetime of the process.
> +	 */
> +	o->loaded_alternates = 0;
> +	odb_prepare_alternates(o);
> +
> +	for (source = o->sources; source; source = source->next)
> +		odb_clear_loose_cache(source);
> +
> +	o->approximate_object_count_valid = 0;
> +
> +	packfile_store_reprepare(o->packfiles);
> +
> +	obj_read_unlock();

...I think I am missing where we call odb_read_lock(). The function
packfile_store_reprepare() has a comment that it must be called under
the odb_read_lock(), but I don't see where we acquire that lock here.

Are the callers of odb_reprepare() supposed to acquire that lock? If so,
it seems a little awkward that the caller is supposed to acquire the
lock, but the callee is the one to release it. Is this function missing
a odb_read_lock() at the top?

I looked at a few callers here and none of them seem to be holding this
lock. pthread_mutex_unlock() is supposed to check that the mutex lock is
held for recursive and error-checking mutexes. IIRC we initialize the
the odb mutex with PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP, so I am a
little surprised that this did not cause a runtime error.

The rest of the patch looks good.

Thanks,
Taylor