<i18n dev> RFR: 8345668: ZoneOffset.ofTotalSeconds performance regression [v3]

[Shaojin Wen]

On Fri, 20 Dec 2024 23:05:06 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fixed compile error
>
> src/java.base/share/classes/java/time/ZoneOffset.java line 428:
> 
>> 426:         if (totalSeconds % (15 * SECONDS_PER_MINUTE) == 0) {
>> 427:             Integer totalSecs = totalSeconds;
>> 428:             ZoneOffset result = SECONDS_CACHE.get(totalSecs);
> 
> Here, each call may allocate an Integer object. The maximum number of ZoneOffsets that need to be cached here is only 148. Using AtomicReferenceArray is better than AtomicConcurrentHashMap.

For example:

    static final class Cache {
              static final AtomicReferenceArray<ZoneOffset> MINUTES_15_CACHE = new AtomicReferenceArray<>(18 * 2 * 4);
    }
    public static ZoneOffset ofTotalSeconds(int totalSeconds) {
        // ...
        int minutes15Rem = totalSeconds / (15 * SECONDS_PER_MINUTE);
        if (totalSeconds - minutes15Rem * 15 * SECONDS_PER_MINUTE == 0) {
            int cacheIndex = minutes15Rem + 18;
            ZoneOffset result = Cache.MINUTES_15_CACHE.get(cacheIndex);
            if (result == null) {
                result = new ZoneOffset(totalSeconds);
                if (!Cache.MINUTES_15_CACHE.compareAndSet(cacheIndex, null, result)) {
                    result = Cache.MINUTES_15_CACHE.get(minutes15Rem);
                }
            }
            return result;
        }
       // ...
    }

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PR Review Comment: https://git.openjdk.org/jdk/pull/22854#discussion_r1894488013