On Mon, 29 Sep 2025 15:08:14 GMT, Kieran Farrell <[email protected]> wrote:
>> With the recent approval of UUIDv7 >> (https://datatracker.ietf.org/doc/rfc9562/), this PR aims to add a new >> static method UUID.timestampUUID() which constructs and returns a UUID in >> support of the new time generated UUID version. >> >> The specification requires embedding the current timestamp in milliseconds >> into the first bits 0–47. The version number in bits 48–51, bits 52–63 are >> available for sub-millisecond precision or for pseudorandom data. The >> variant is set in bits 64–65. The remaining bits 66–127 are free to use for >> more pseudorandom data or to employ a counter based approach for increased >> time percision >> (https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-7). >> >> The choice of implementation comes down to balancing the sensitivity level >> of being able to distingush UUIDs created below <1ms apart with performance. >> A test simulating a high-concurrency environment with 4 threads generating >> 10000 UUIDv7 values in parallel to measure the collision rate of each >> implementation (the amount of times the time based portion of the UUID was >> not unique and entries could not distinguished by time) yeilded the >> following results for each implemtation: >> >> >> - random-byte-only - 99.8% >> - higher-precision - 3.5% >> - counter-based - 0% >> >> >> Performance tests show a decrease in performance as expected with the >> counter based implementation due to the introduction of synchronization: >> >> - random-byte-only 143.487 ± 10.932 ns/op >> - higher-precision 149.651 ± 8.438 ns/op >> - counter-based 245.036 ± 2.943 ns/op >> >> The best balance here might be to employ a higher-precision implementation >> as the large increase in time sensitivity comes at a very slight performance >> cost. > > Kieran Farrell has updated the pull request incrementally with one additional > commit since the last revision: > > missing semicolon test/jdk/java/util/UUID/UUIDTest.java line 211: > 209: try { > 210: long now = System.currentTimeMillis(); > 211: UUID u = UUID.epochMillis(now); Please also add a assert for non-null `u`. test/jdk/java/util/UUID/UUIDTest.java line 213: > 211: UUID u = UUID.epochMillis(now); > 212: } catch (Exception e) { > 213: throw new AssertionError("Unexpected exception with valid > timestamp: " + e); Please also include the timestamp value in the exception message to help debugging if at all this ever fails. Also at a few other places in the newly introduced code in this test where we throw any exception due to test failure. test/jdk/java/util/UUID/UUIDTest.java line 224: > 222: // Should throw for timestamp > 48 bits > 223: try { > 224: UUID.epochMillis(1L << 48); Can you also include a test for the exact 48 bit (allowed) value and assert that it is accepted by this method and a non-null UUID instance is returned? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2390006514 PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2390007505 PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2390005257
