RFR: 8305092: Improve Thread.sleep(millis, nanos) for sub-millisecond granularity [v12]

[David Holmes]

On Wed, 26 Apr 2023 20:22:54 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Java API has the `Thread.sleep(millis, nanos)` method exposed to users. The documentation for that method clearly says the precision and accuracy are dependent on the underlying system behavior. However, it always rounds up `nanos` to 1ms when doing the actual sleep. This means users cannot do the micro-second precision sleeps, even when the underlying platform allows it. Sub-millisecond sleeps are useful to build interesting primitives, like the rate limiters that run with >1000 RPS.
>> 
>> When faced with this, some users reach for more awkward APIs like `java.util.concurrent.locks.LockSupport.parkNanos`. The use of that API for sleeps is not in line with its intent, and while it "seems to work", it might have interesting interactions with other uses of `LockSupport`. Additionally, these "sleeps" are no longer visible to monitoring tools as "normal sleeps", e.g. as `Thread.sleep` events. Therefore, it would be prudent to improve current `Thread.sleep(millis, nanos)` for sub-millisecond granularity. 
>> 
>> Fortunately, the underlying code is almost ready for this, at least on POSIX side. I skipped Windows paths, because its timers are still no good. Note that on both Linux and MacOS timers oversleep by about 50us. I have a few ideas how to improve the accuracy for them, which would be a topic for a separate PR.
>> 
>> Additional testing:
>>   - [x] New regression test
>>   - [x] New benchmark
>>   - [x] Linux x86_64 `tier1`
>>   - [x] Linux AArch64 `tier1`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 26 commits:
> 
>  - Merge branch 'master' into JDK-83050920-thread-sleep-subms
>  - Merge branch 'master' into JDK-83050920-thread-sleep-subms
>  - Fix Amazon copyright
>  - Merge branch 'master' into JDK-83050920-thread-sleep-subms
>  - Drop nanos_to_nanos_bounded
>  - Handle overflows
>  - More review comments
>  - Adjust test times
>  - Windows again
>  - Windows fixes: align(...) is only for power-of-two alignments
>  - ... and 16 more: https://git.openjdk.org/jdk/compare/35e7bc21...da8f0f8c

Nothing further from me. Thanks.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13225#pullrequestreview-1403054308