<i18n dev> RFR: 8276220: Reduce excessive allocations in DateTimeFormatter [v10]

[Claes Redestad]

On Wed, 3 Nov 2021 21:57:44 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Prompted by a request from Volkan Yazıcı I took a look at why the java.time formatters are less efficient for some common patterns than custom formatters in apache-commons and log4j. This patch reduces the gap, without having looked at the third party implementations. 
>> 
>> When printing times:
>> - Avoid turning integral values into `String`s before appending them to the buffer 
>> - Specialize `appendFraction` for `NANO_OF_SECOND` to avoid use of `BigDecimal`
>> 
>> This means a speed-up and reduction in allocations when formatting almost any date or time pattern, and especially so when including sub-second parts (`S-SSSSSSSSS`).
>> 
>> Much of the remaining overhead can be traced to the need to create a `DateTimePrintContext` and adjusting `Instant`s into a `ZonedDateTime` internally. We could likely also win performance by specializing some common patterns.
>> 
>> Testing: tier1-3
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove accidentally committed experimental @Stable (no effect on micros)

Thanks, Naoto!

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PR: https://git.openjdk.java.net/jdk/pull/6188