On Wed, 29 Mar 2023 18:10:30 GMT, Alan Bateman <al...@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` > > src/java.base/share/classes/java/lang/Thread.java line 509: > >> 507: ThreadSleepEvent event = new ThreadSleepEvent(); >> 508: try { >> 509: event.time = MILLISECONDS.toNanos(millis) + nanos; > > This can overflow when millis is at or close to Long.MAX_VALUE. Yes, let me fix that. `TimeUnit.toNanos` handles it well itself, it seems. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/13225#discussion_r1152336826