Re: [PATCH v2 2/2] oidset: use khash

["René Scharfe" <l.s.r@web.de>]

Am 03.10.2018 um 21:40 schrieb Jeff King:
> On Wed, Oct 03, 2018 at 03:16:39PM +0200, René Scharfe wrote:
>> diff --git a/fetch-pack.c b/fetch-pack.c
>> index 75047a4b2a..a839315726 100644
>> --- a/fetch-pack.c
>> +++ b/fetch-pack.c
>> @@ -536,7 +536,7 @@ static int tip_oids_contain(struct oidset *tip_oids,
>>  	 * add to "newlist" between calls, the additions will always be for
>>  	 * oids that are already in the set.
>>  	 */
>> -	if (!tip_oids->map.map.tablesize) {
>> +	if (!tip_oids->set.n_buckets) {
>>  		add_refs_to_oidset(tip_oids, unmatched);
>>  		add_refs_to_oidset(tip_oids, newlist);
>>  	}
> 
> This is a little intimate with the implementation of khash, but I think
> it's probably OK (and really no worse than what was there before).
> 
> As the comment above notes, I think we're really looking at the case
> where this gets populated on the first call, but not subsequent ones. It
> might be less hacky to use a "static int initialized" here. Or if we
> want to avoid hidden globals, put the logic into filter_refs() to decide
> when to populate.

Right.  I'd prefer the latter, but was unable to find a nice way that
still populates the oidset lazily.  It's certainly worth another look,
and a separate series.

>> diff --git a/oidset.h b/oidset.h
>> index 40ec5f87fe..4b90540cd4 100644
>> --- a/oidset.h
>> +++ b/oidset.h
>> [...]
>> +KHASH_INIT(oid, struct object_id, int, 0, oid_hash, oid_equal)
> 
> This will declare these "static inline". Our other major "macros become
> inline functions" code is commit-slab.h, and there we found it necessary
> to add MAYBE_UNUSED. I wonder if we ought to be doing the same here (I
> don't get any warnings, but I suspect sparse might complain).

I doubt it (but didn't check) because khash.h defines kh_clear_##name(),
which we don't use it anywhere and there have been no complaints so far.
And if we wanted to add MAYBE_UNUSED then the right place for that would
be in KHASH_INIT, no?

> It might be nice if these functions could hide inside oidset.c (and just
> declare the struct here). It looks like we might be able to do that with
> __KHASH_TYPE(), but the double-underscore implies that we're not
> supposed to. ;)
> 
> I guess we also use a few of them in our inlines here. I'm not 100% sure
> that oidset_* needs to be inlined either, but this is at least a pretty
> faithful conversion of the original.

We could inline all of the oidset functions, following the spirit of
klib/khash.h.

Or we could uninline all of them and then may be able to clean up
oidset.h by using KHASH_DECLARE.  Perhaps we'd need to guard with an
"#ifndef THIS_IS_OIDSET_C" or similar to avoid a clash with KHASH_INIT.

Not sure if any of that would be a worthwhile improvement..

René