Re: [PATCH v3 2/5] fetch-pack: load tip_oids eagerly iff needed

[Jeff King <peff@peff.net>]

On Thu, Oct 04, 2018 at 05:09:39PM +0200, René Scharfe wrote:

> tip_oids_contain() lazily loads refs into an oidset at its first call.
> It abuses the internal (sub)member .map.tablesize of that oidset to
> check if it has done that already.
> 
> Determine if the oidset needs to be populated upfront and then do that
> instead.  This duplicates a loop, but simplifies the existing one by
> separating concerns between the two.

I like this approach much better than what I showed earlier. But...

> diff --git a/fetch-pack.c b/fetch-pack.c
> index 3b317952f0..53914563b5 100644
> --- a/fetch-pack.c
> +++ b/fetch-pack.c
> @@ -526,23 +526,6 @@ static void add_refs_to_oidset(struct oidset *oids, struct ref *refs)
>  		oidset_insert(oids, &refs->old_oid);
>  }
>  
> -static int tip_oids_contain(struct oidset *tip_oids,
> -			    struct ref *unmatched, struct ref *newlist,
> -			    const struct object_id *id)
> -{
> -	/*
> -	 * Note that this only looks at the ref lists the first time it's
> -	 * called. This works out in filter_refs() because even though it may
> -	 * add to "newlist" between calls, the additions will always be for
> -	 * oids that are already in the set.
> -	 */

I don't think the subtle point this comment is making goes away. We're
still growing the list in the loop that calls tip_oids_contain() (and
which now calls just oidset_contains). That's OK for the reasons given
here, but I think that would need to be moved down to this code:

> +	if (strict) {
> +		for (i = 0; i < nr_sought; i++) {
> +			ref = sought[i];
> +			if (!is_unmatched_ref(ref))
> +				continue;
> +
> +			add_refs_to_oidset(&tip_oids, unmatched);
> +			add_refs_to_oidset(&tip_oids, newlist);
> +			break;
> +		}
> +	}

I.e., we need to say here why it's OK to summarize newlist in the
oidset, even though we're adding to it later.

-Peff