On Wed, 11 Jan 2023 13:23:44 GMT, fabioromano1 <d...@openjdk.org> wrote:
>> src/java.base/share/classes/java/util/BitSet.java line 421: >> >>> 419: final long bitMask = 1L << bitIndex; >>> 420: words[wordIndex] ^= bitMask; >>> 421: cardinality += (words[wordIndex] & bitMask) != 0 ? 1 : -1; >> >> Isn't there a race condition here? >> >> I'm wondering if it would not be better to cache the last cardinality and >> invalidate (negative cardinality) when the bit set is changed. Less >> intrusive and potentially quicker. > > 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) ------------- PR: https://git.openjdk.org/jdk/pull/11837
