RFR: JDK-8310502 : Optimization for j.l.Long.fastUUID() [v25]

[Glavo]

On Tue, 27 Jun 2023 11:25:32 GMT, 温绍锦 <duke at openjdk.org> wrote:

>> 温绍锦 has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   use ISO_8859_1.INSTANCE directly instead of StandardCharsets.ISO_8859_1
>
>> I'm looking through [[6b61a71](https://github.com/openjdk/jdk/commit/6b61a715caeeb586d5480a3a70f90bd1811d1335)], update 24.
>> 
>> Moving fastUUID out of Long is good.
>> 
>> UUID::toString can use StandardCharsets. ISO_8859_1, no need to use sun.nio.cs code here.
>> 
>> The list of imports in java.util.UUID is a bit messy now, can you clean this up.
>> 
>> It's confusing to have java.util.HexDigits and jdk.internal.util.HexDigits. It also creates an inconsistency with DecimalDigits and OctalDigits as the latter encapsulate their arrays. I assume you've done this to allow sharing of the 256 element array. I don't object to move the array to a supporting class but it needs to be renamed and the class description replaced as it is not a Digits implementation. Adding a private constructor would help make it clear that it should not be instantiated.
> 
> very good suggestion, i have modified it according to your suggestion.

> @wenshao - adding a jdk.internal.digits package for this tiny class is overkill. For this PR, the simplest thing is to revert the changes to HexDigit, remove jdk.internal.digits.Hex256 and just put a small holder class in UUID for use by UUID.toString. That would be my preference to avoid splitting up HexDigits and creating inconsistencies in code used for string templates.

Wenshao hopes to use this array for other optimizations in `java.lang` in the future.

But as for this PR, I suggest wenshao not to do so much. I suggest moving `DIGITS` back to `HexDigits` first to make the modifications in this PR smaller. Reducing modifications helps with faster review.

When you need to optimize the classes in `java.lang`, we will continue to discuss how to share these arrays more safely and efficiently.

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PR Comment: https://git.openjdk.org/jdk/pull/14578#issuecomment-1609857054