RFR [8005953] Speedup construction of CopyOnWriteArraySet in special cases

[Jason Mehrens]

Ivan,

> The addAllAbsent() function has O(c.length^2) complexity, so
> construction time quickly grows with the input size.
> However, if we knew that c is a Set, we could construct the COWAS in
> linear time.

You have to be able to prove that the given Set uses the same equivalence relation as the COWAS.  Otherwise, it will fall apart you pass a SortedSet with a Comparator or an identity set.

> And if the c was known to be another COWAS, we could simply clone the
> underlying CopyOnWriteArrayList.

That would be safe.

Jason