RFR: 8334015: Add Support for UUID Version 7 (UUIDv7) defined in RFC 9562 [v16]

[Roger Riggs]

On Wed, 21 May 2025 14:10:31 GMT, Kieran Farrell <kfarrell at openjdk.org> wrote:

>>> if so, I've tried out some variations, i found creating the 64 bit lsb with ng.nextLong() brings a large pefomance decrease over using the nextBytes method
>> 
>> Probably because `SecureRandom` gets `#nextLong()` from `Random`, which ends up calling `#next(int)` twice, so it allocates twice. Overriding `#nextLong()` in `SecureRandom` may help a little but will still have to allocate as long as `SecureRandomSpi` is not updated.
>
> The nsBytes were included to give some additional but not guaranteed monotonicity in the event of msTime collisions on a single instance of a JVM. I updated the method to print the msTime and nsBits for visual purposes seen below. The nsBits increase until cycling back to a lower value on the last or +/- 1 of the last instance of the same msTime value as tested on Linux and MacOS . I'm not sure of the reason why the cycles are almost in sync given that the times are not linked. However Marschall has pointed out that nanoTime() resolution is weaker on windows so maybe its not something that can be depended on. In that case I could revert to the random byte only implementation and remove the nsBytes fro random data.
> 
> As for the nsBits computation, in order to align with the RFC, my understanding was to get the remainder of nsTime (% 1_000_000) to get the nanoseconds within the current millisecond, divide by 1_000_000 to convert to a fraction of a ms and multiply by 4096L to scale to the integer range to fit into the 12 bits permitted for the ns timestamp. 
> 
> 
> 
> 
> msTime: 1747835228108, nsBits: 1336
> msTime: 1747835228137, nsBits: 1333
> msTime: 1747835228137, nsBits: 1794
> msTime: 1747835228137, nsBits: 2206
> msTime: 1747835228137, nsBits: 2766
> msTime: 1747835228137, nsBits: 3040
> msTime: 1747835228137, nsBits: 3485
> msTime: 1747835228137, nsBits: 3901
> msTime: 1747835228138, nsBits: 239
> msTime: 1747835228138, nsBits: 651
> msTime: 1747835228138, nsBits: 918
> msTime: 1747835228138, nsBits: 1321
> msTime: 1747835228138, nsBits: 1729
> msTime: 1747835228138, nsBits: 2140
> msTime: 1747835228138, nsBits: 2535
> msTime: 1747835228138, nsBits: 2874
> msTime: 1747835228138, nsBits: 3243
> msTime: 1747835228138, nsBits: 3641
> msTime: 1747835228138, nsBits: 3967
> msTime: 1747835228139, nsBits: 227
> msTime: 1747835228139, nsBits: 524

This thread can be resolved.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2389015266