ObjectSynchronizer iterate only in-use monitors?

[Robbin Ehn]

On 05/16/2017 01:37 PM, Carsten Varming wrote:
> 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/

Interesting, and a bit scary, I'll need to take a deeper look.

Thanks!

/Robbin

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