ObjectSynchronizer iterate only in-use monitors?

[Roman Kennke]

Am 11.05.2017 um 09:44 schrieb Robbin Ehn:
> Hi,
>
> We have actually been discussing this last few days:
>
> https://bugs.openjdk.java.net/browse/JDK-8153224

We are seeing the exact same issue as mentioned in the bug report too.
Sometimes, time-to-safepoint is very high, in the area of ~200ms. The
reason for this seems to be deflate_idle_monitors().

In the current implementation, the VM thread iterates over all threads,
and deflates each thread's idle monitors one after another.

I would rather have each Java thread deflate its own idle monitors
before arriving at a safepoint. This should be much faster because
higher chances a thread has its own monitors in cache, and deflation
processing is done in parallel too. This requires some thought... e.g.
what to do with non-runnable threads.

If you think that's a good way to go, and don't already have a fix in
the pipeline, I can take on the bug. I've got synchronizer still hot in
memory, and experimented with self-processing Java threads before
safepoint a while back too.

Let me know!

Roman