Review for CR 6728865 : Improved heuristics for Collections.disjoint() [updated]

[Mike Duigou]

I've updated the webrev with Ulf's feedback. http://cr.openjdk.java.net/~mduigou/6728865.2/webrev/

The old heuristics:

1. If c1 is a Set then iterate over c2.

2. Iterate over the smaller Collection.


I believe that the || in the original should have been a &&

I've rearranged it as branches in my revision.


The new heuristics:

1. If c1 is a Set then iterate over c2.

2. If c2 is a Set then iterate over c1.

3. If either collection is empty then result is always true.

4. Iterate over the smaller Collection.

Mike



On Dec 19 2010, at 16:42 , David Holmes wrote:

> Hi Mike,
> 
> Mike Duigou said the following on 12/20/10 10:29:
>> I have updated the webrev for CR 6728865 with Rémi's feedback. The new webrev is at:
>> http://cr.openjdk.java.net/~mduigou/6728865.1/webrev/
>> The size() comparisons are now done only when both c1 and c2 are not sets and I have removed the isEmpty() micro-optimization.
> 
> So to summarise this change:
> 
> 1. The original code checked for c1 being a set and not c2, but not vice-versa - this fixes that
> 
> 2. This code adds an optimization when they are both not sets but at least one is empty
> 
> Did I miss anything?
> 
> Seems functionally sound to me, but I can't attest to any performance benefits.
> 
> Cheers,
> David Holmes