ObjectSynchronizer iterate only in-use monitors?

[Carsten Varming]

FYI. Last year I wrote a small patch[1] against JDK9 that enables monitor
deflation to happen outside a safepoint. There was little interest then, so
I never proposed it as a patch. The JDK9 code has moved on a little bit, so
the patch probably doesn't apply cleanly, but the patch shows one way to
complete the life of a monitor without going through a safepoint.

Carsten

[1] http://cr.openjdk.java.net/~cvarming/monitor_deflate_conc/0/

On Tue, May 16, 2017 at 6:32 AM, Roman Kennke <rkennke at redhat.com> wrote:

> Am 16.05.2017 um 11:48 schrieb Robbin Ehn:
> > Correction,
> >
> > On 05/16/2017 11:45 AM, Robbin Ehn wrote:
> >> Yes, but since we are at a safepoint you should be able to use gc
> >> worker in that case also?
> >
> > or the java thread. And scratch 'also' :)
>
> This clearly requires co-operation from the GC.
>
> Also, I noticed that some GCs cannot do deflation during root scanning,
> because they stow away mark words during marking, and temporarily store
> forwarding pointers into the mark words, and only restore mark words
> after GC. This obviously conflicts with monitor deflation. Which means
> we need some GC cooperation there too... I will figure something out.
>
> Roman
>
>