RFR: 8348880: Replace ConcurrentMap with AtomicReferenceArray for ZoneOffset.MINUTES_15_CACHE [v3]

[Chen Liang]

On Tue, 28 Jan 2025 16:44:17 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> ZoneOffset.MINUTES_15_CACHE uses AtomicReferenceArray to replace ConcurrentMap to avoid object allocation caused by boxing from int to Integer during access.
>
> Shaojin Wen has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - simplify
>  - MINUTES_15_CACHE -> QUARTER_CACHE

src/java.base/share/classes/java/time/ZoneOffset.java line 138:

> 136:         implements TemporalAccessor, TemporalAdjuster, Comparable<ZoneOffset>, Serializable {
> 137: 
> 138:     /** Cache of time-zone offset by offset in seconds. */

Suggestion:

    /** Cache of time-zone offset by offset in quarters. */

src/java.base/share/classes/java/time/ZoneOffset.java line 431:

> 429:         int quarters = totalSeconds / SECONDS_PER_QUARTER;
> 430:         if (totalSeconds - quarters * SECONDS_PER_QUARTER == 0) {
> 431:             ZoneOffset result = QUARTER_CACHE.getOpaque(quarters & 0xff);

For the ease of future maintenance, I recommend replacing `quarters & 0xFF` with a new variable `key`:

// quarters range from -72 to 72.
// & 0xFF maps them to 0-72 and 184-255.
int key = quarters & 0xFF;

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PR Review Comment: https://git.openjdk.org/jdk/pull/23337#discussion_r1932514778
PR Review Comment: https://git.openjdk.org/jdk/pull/23337#discussion_r1932526383