On Tue, 31 Jan 2023 15:57:43 GMT, Per Minborg <[email protected]> wrote:
> `ZoneOffset` instances are cached by the `ZoneOffset` class itself for values
> in the range [-18h, 18h] for each second that is on an even quarter of an
> hour (i.e. at most 2*18*4+1 = 145 values).
>
> Instead of using a `ConcurrentHashMap` for caching instanced, we could
> instead use an `AtomicReferenceArray` with direct slot value access for said
> even seconds. This will improve performance and reduce the number of object
> even though the backing array will go from an initial 32 in the CHM to an
> initial/final 145 in the ARA. The CHM will contain much more objects and
> array slots for typical numbers of entries in the cache and will compute
> hash/bucket/collision on the hot code path for each cache access.
src/java.base/share/classes/java/time/ZoneOffset.java line 432:
> 430: if (totalSeconds % (15 * SECONDS_PER_MINUTE) == 0) {
> 431: int slot = cacheSlot(totalSeconds);
> 432: ZoneOffset cached = SECONDS_CACHE.get(slot);
I miss `AtomicReferenceArray::computeIfNull` that atomically will compute an
element if the value at a certain index is `null`.
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PR: https://git.openjdk.org/jdk/pull/12346
