On Wed, 28 May 2025 17:11:31 GMT, kieran-farrell <d...@openjdk.org> wrote:
>> The `timestamp` method may mislead an app developer thinking its the time >> from the version 7 timestamp. >> The first-line comment might make it more obvious if it says: >> `The timestamp value associated with a version 1 UUID.` >> >> The Unix Epoch time would be easier to use if a method was added to return >> it. >> `long UnixEpochTimeNanos()` (name subject to bike-shedding). >> And throwing if it was not version 7. > > The first 48 bits need to be from the unix epoch time stamp in ms only to > remain complaint. If I understand correctly, to be able to guarantee that the > nsBits are actually time orderable, System.nanoTime() would have to be pinned > to a point where System.currentTimeMillis() increments by 1ms (which doesnt > seem possible). Otherwise any offset could be at any arbitrary point in a > given millisecond and nsBits would wrap around from that. > > I think the options are to either use the random only approach with ms > precision or an guaranteed monotonic counter based approach and take the hit > on performance. > > I agree with updating to "create" from "retrieve" on the first line comment > and also with the method name change to avoid confusion with UUIDv1, however > to either unixEpochTimeNanos() or unixEpochTimeMillis() or otherwise > depending on which implementation we settle on. We don't have a reliable sub-microsecond source across platforms, so can only be confident using random numbers for the low order bits. (and I don't expect a higher resolution monotonic clock to be available anytime soon). Would the static factory method be more useful if it took the mstime as a parameter? That would allow the caller to pick the time source. For example, ` UUID ts = UUID.timesteampUUID(System.currentTimeMillis());` It would avoid locking into the System.currentTimeMillis() and allows the application to create UUIDs for whatever time meets its needs. Adding a unixEpochTimeMillis() makes sense, re-assembling the time bits into the ms time. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2112737649
