RFR: 8288723: Avoid redundant ConcurrentHashMap.get call in java.time

[liach]

On Mon, 20 Jun 2022 09:11:31 GMT, Attila Szegedi <attila at openjdk.org> wrote:

>> Instead of separate ConcurrentHashMap.get call, we can use result of previous putIfAbsent call.
>
> src/java.base/share/classes/java/time/format/DateTimeTextProvider.java line 319:
> 
>> 317:                 store = prev;
>> 318:             }
>> 319:         }
> 
> You could do better here and use `computeIfAbsent` with `createStore` as its lambda. You could even change the signature of `createStore` to take `Entry<TemporalField, Locale>` as its parameter and then you could have this method be:
> 
>     private Object findStore(TemporalField field, Locale locale) {
>         return CACHE.computeIfAbsent(createEntry(field, locale), this::createStore);
>     }
> 
>     ...
> 
>     private Object createStore(Entry<TemporalField, Locale> entry) {
>         ...
>     }
> 
> This applies to most other changes you made, the one in `ZoneOffset` is the only one that's slightly different because there you have adjustment of `ID_CACHE` too.

This behaves slightly different from the old initialization; the concurrent hash map blocks when the mapping function is run, just in case if non-blocking instantiation is what we want. If that's not a problem, I would prefer szegedi's suggestion.

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PR: https://git.openjdk.org/jdk/pull/9208