On Wed, 11 Jan 2023 12:57:47 GMT, Jim Laskey <[email protected]> wrote:
>> The enanchment is useful for applications that make heavy use of BitSet
>> objects as sets of integers, and therefore they need to make a lot of calls
>> to cardinality() method, which actually require linear time in the number of
>> words in use by the bit set.
>> This optimization reduces the cost of calling cardinality() to constant
>> time, as it simply returns the value of the field, and it also try to make
>> as little effort as possible to update the field, when needed.
>>
>> Moreover, it has been implemented a new method for testing wheter a bit set
>> includes another bit set (i.e., the set of true bits of the parameter is a
>> subset of the true bits of the instance).
>
> src/java.base/share/classes/java/util/BitSet.java line 185:
>
>> 183: private BitSet(long[] words) {
>> 184: this.words = words;
>> 185: wordsInUse = words.length;
>
> Why did you drop the `this.` in front of wordsInUse? (non-standard)
Simply an oversight.
> 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
-------------
PR: https://git.openjdk.org/jdk/pull/11837
