RFR: 8305092: Improve Thread.sleep(millis, nanos) for sub-millisecond granularity [v9]

[Aleksey Shipilev]

On Thu, 20 Apr 2023 09:29:43 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 incrementally with one additional commit since the last revision:
> 
>   Handle overflows

While writing the CSR, I realized we still need to keep the `MAX_SECS` cap at POSIX path for individual sleeps, if only to care for downstream Solaris ports that are still maintained. We also would like to care about accidentally calling `JavaThread::sleep(jlong millis)` with e.g. `max_jlong`. New commit should handle both.

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PR Comment: https://git.openjdk.org/jdk/pull/13225#issuecomment-1516018689