RFR (jdk10): JDK-8180175: ObjectSynchronizer only needs to iterate in-use monitors

[Aleksey Shipilev]

On 05/11/2017 12:08 PM, Roman Kennke wrote:
> Performance-wise it makes a very significant difference (running
> gc-bench's roots.Sync test, which exaggerates synchronizer usage, with
> Shenandoah):
> 
> baseline:
> S: Thread Roots 37748 us
> S: Synchronizer Roots 15115 us
> UR: Thread Roots 24967 us
> UR: Synchronizer Roots 11906 us
> 
> patched:
> S: Thread Roots 40365 us
> S: Synchronizer Roots 0 us
> UR: Thread Roots 24459 us
> UR: Synchronizer Roots 0 us

This also cuts Shenandoah's pauses at least 2x on SPECjbb2015 -- so it is not
just some glitch that helps a targeted test. I fully expect the same 10 ms
improvement to be visible in pause times for other OpenJDK GCs on workloads like
these.

Thanks,
-Aleksey