RFR: 8308804: Improve UUID.randomUUID performance with bulk/scalable PRNG access [v7]

[Aleksey Shipilev]

On Thu, 1 Jun 2023 12:59:14 GMT, Brett Okken <duke at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 13 commits:
>> 
>>  - Revert test changes
>>  - Merge branch 'master' into JDK-8308804-uuid-buffers
>>  - Simplify clinit
>>  - Remove the properties
>>  - Swap lsb/msb
>>  - Fine-tune exceptions
>>  - Handle privileged properties
>>  - Use ByteArray to convert. Do version/variant preparations straight on locals. Move init out of optimistic lock section.
>>  - More touchups
>>  - Comment updates
>>  - ... and 3 more: https://git.openjdk.org/jdk/compare/4460429d...fd7eaa1a
>
> src/java.base/share/classes/java/util/UUID.java line 234:
> 
>> 232:                     long msb = ByteArray.getLong(buf, 0);
>> 233:                     long lsb = ByteArray.getLong(buf, 8);
>> 234:                     return fromRandom(msb, lsb);
> 
> is there any value in moving this outside of the critical section?

I have tried it before, and it gives no benefit, but significantly complicates the code. This is the part under write lock, where we have spent a significant time refilling the buffer. The little improvement we might get here is drowning in those costs.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/14135#discussion_r1213121408