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

["René Scharfe" <l.s.r@web.de>]

Am 04.10.2018 um 23:38 schrieb Jonathan Tan:
>> 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.
> 
> [snip]
> 
>> +	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;
>> +		}
>> +	}
>> +
>>  	/* Append unmatched requests to the list */
>>  	for (i = 0; i < nr_sought; i++) {
>>  		ref = sought[i];
>>  		if (!is_unmatched_ref(ref))
>>  			continue;
>>  
>> -		if ((allow_unadvertised_object_request &
>> -		     (ALLOW_TIP_SHA1 | ALLOW_REACHABLE_SHA1)) ||
>> -		    tip_oids_contain(&tip_oids, unmatched, newlist,
>> -				     &ref->old_oid)) {
>> +		if (!strict || oidset_contains(&tip_oids, &ref->old_oid)) {
>>  			ref->match_status = REF_MATCHED;
>>  			*newtail = copy_ref(ref);
>>  			newtail = &(*newtail)->next;
> 
> I don't think the concerns are truly separated - the first loop quoted
> needs to know that in the second loop, tip_oids is accessed only if
> there is at least one unmatched ref.

Right, the two loops are still closely related, but only the first one
is concerned with loading refs.

For a true separation we could first build a list of unmatched refs and
then loop through that instead of `sought`.  Not sure if that's better,
but maybe the overhead I imagine it would introduce isn't all that big.

> Would it be better to expose the
> size of the oidset and then use it in place of
> "tip_oids->map.map.tablesize"? Checking for initialization (using
> "tablesize") is conceptually different from checking the size, but in
> this code, both initialization and the first increase in size occur upon
> the first oidset_insert(), so we should still get the same result.

It would work in practice.  If there are no refs to load then it would
try to load those zero refs for each unmatched ref, which shouldn't
really be a problem, but I still find it a wee bit sloppy.  Too
theoretical?

René