> 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: Windows fixes: align(...) is only for power-of-two alignments ------------- Changes: - all: https://git.openjdk.org/jdk/pull/13225/files - new: https://git.openjdk.org/jdk/pull/13225/files/f78aef54..29c7df36 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=13225&range=04 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13225&range=03-04 Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod Patch: https://git.openjdk.org/jdk/pull/13225.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/13225/head:pull/13225 PR: https://git.openjdk.org/jdk/pull/13225
