RFR: 8300487: Store cardinality as a field in BitSet

[fabioromano1]

On Wed, 11 Jan 2023 15:33:47 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> I agree with the fact that is less intrusive, but certainly not potentially quicker, since the complete recalculation of cardinality requires linear time in the value of wordsInUse
>
> A perhaps slightly less racy way would be to only read and write from `words` once:
> 
> final long newValue = words[wordIndex] ^ bitMask;
> cardinality += (newValue & bitMask) != 0 ? 1 : -1;
> words[wordIndex] = newValue;
> 
> .. but the fact remains that `BitSet` is not thread-safe, so I think we shouldn't complicate things to avoid or eliminate potential races. (Using a local might help the compiler to avoid the back-to-back array read, but probably doesn't matter)

I think the same of @cl4es.

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PR: https://git.openjdk.org/jdk/pull/11837