RFR: 8310502 : optimization for UUID#toString

[温绍锦]

On Wed, 21 Jun 2023 07:58:11 GMT, Alan Bateman <alanb 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
>
> src/java.base/share/classes/java/lang/Long.java line 97:
> 
>> 95:                     + (lo < 10 ? '0' + lo : 'a' + lo - 10));
>> 96:         }
>> 97:     }
> 
> Are you checking the impact on startup? I guess I would have expected to see it loaded from the CDS archive. Given that the usage is just UUID::toString then maybe you could move this to a holder class containing a Stable array, at least until there is a better way to have lazily computed constants. Another thing to try is moving fastUUID out of Long - moving to an array of precomputed hex values means it is not tied to Long internals anymore.

1. HEX256 can be used to optimize all integers to hex strings, such as Integer#toHexString and Long#toHexString and byte [] to hexstring.

2. i am a newcomer, and i don't understand what 'loaded from the CDS archive' means, do you mean to use constants instead? such as

HEX256 = new char[]{
        12336, 12337, 12338, 12339, 12340, 12341, 12342, 12343, 12344, 12345,
        12385, 12386, 12387, 12388, 12389, 12390, 12592, 12593, 12594, 12595,
        12596, 12597, 12598, 12599, 12600, 12601, 12641, 12642, 12643, 12644,
        12645, 12646, 12848, 12849, 12850, 12851, 12852, 12853, 12854, 12855,
        12856, 12857, 12897, 12898, 12899, 12900, 12901, 12902, 13104, 13105,
        13106, 13107, 13108, 13109, 13110, 13111, 13112, 13113, 13153, 13154,
        13155, 13156, 13157, 13158, 13360, 13361, 13362, 13363, 13364, 13365,
        13366, 13367, 13368, 13369, 13409, 13410, 13411, 13412, 13413, 13414,
        13616, 13617, 13618, 13619, 13620, 13621, 13622, 13623, 13624, 13625,
        13665, 13666, 13667, 13668, 13669, 13670, 13872, 13873, 13874, 13875,
        13876, 13877, 13878, 13879, 13880, 13881, 13921, 13922, 13923, 13924,
        13925, 13926, 14128, 14129, 14130, 14131, 14132, 14133, 14134, 14135,
        14136, 14137, 14177, 14178, 14179, 14180, 14181, 14182, 14384, 14385,
        14386, 14387, 14388, 14389, 14390, 14391, 14392, 14393, 14433, 14434,
        14435, 14436, 14437, 14438, 14640, 14641, 14642, 14643, 14644, 14645,
        14646, 14647, 14648, 14649, 14689, 14690, 14691, 14692, 14693, 14694,
        24880, 24881, 24882, 24883, 24884, 24885, 24886, 24887, 24888, 24889,
        24929, 24930, 24931, 24932, 24933, 24934, 25136, 25137, 25138, 25139,
        25140, 25141, 25142, 25143, 25144, 25145, 25185, 25186, 25187, 25188,
        25189, 25190, 25392, 25393, 25394, 25395, 25396, 25397, 25398, 25399,
        25400, 25401, 25441, 25442, 25443, 25444, 25445, 25446, 25648, 25649,
        25650, 25651, 25652, 25653, 25654, 25655, 25656, 25657, 25697, 25698,
        25699, 25700, 25701, 25702, 25904, 25905, 25906, 25907, 25908, 25909,
        25910, 25911, 25912, 25913, 25953, 25954, 25955, 25956, 25957, 25958,
        26160, 26161, 26162, 26163, 26164, 26165, 26166, 26167, 26168, 26169,
        26209, 26210, 26211, 26212, 26213, 26214
};

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PR Review Comment: https://git.openjdk.org/jdk/pull/14578#discussion_r1236632961