RFR: JDK-8310502 : Optimization for j.l.Long.fastUUID() [v22]

[ExE Boss]

On Sun, 25 Jun 2023 12:20:17 GMT, 温绍锦 <duke at openjdk.org> wrote:

>> By optimizing the implementation of java.lang.Long#fastUUID, the performance of the java.util.UUID#toString method can be significantly improved.
>> 
>> The following are the test results of JMH: 
>> 
>> Benchmark                     Mode  Cnt      Score      Error   Units
>> UUIDUtilsBenchmark.new       thrpt    5  92676.550 ±  292.213  ops/ms
>> UUIDUtilsBenchmark.original  thrpt    5  37040.165 ± 1023.532  ops/ms
>
> 温绍锦 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add jdk.util.HexDigits, sharing cache array across multiple classes, including :
>   java.lang.Long#fastUUID
>   java.util.HexDigits
>   java.lang.Long#toHexString(future)
>   java.lang.Integer#toHexString(future)
>   java.util.HexFormat(future)

src/java.base/share/classes/java/lang/Long.java line 451:

> 449:     }
> 450: 
> 451:     static String fastUUID(long lsb, long msb) {

This method should probably have an assert or something that `COMPACT_STRINGS` is `true`, e.g.:
Suggestion:

    static String fastUUID(long lsb, long msb) {
        if (!COMPACT_STRINGS) {
            throw new InternalError("Long::fastUUID requires compact strings");
        }

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

PR Review Comment: https://git.openjdk.org/jdk/pull/14578#discussion_r1241232478