RFR 8247808: Move JVMTI strong oops to OopStorage

[David Holmes]

Hi Coleen,

On 18/06/2020 7:25 am, coleen.phillimore at oracle.com wrote:
> Summary: Remove JVMTI oops_do calls from JVMTI and GCs
> 
> Tested with tier1-3, also built shenandoah to verify shenandoah changes.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/2020/8247808.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8247808

This is a nice cleanup and simplification of the code for working with 
OopStorage! So LGTM.

One query ... I'm assuming that the processing previously done in 
JvmtiExport::oops_do is now done by OopStorageSet::vm_global()->oops_do. 
In most cases I can see the call to OopStorageSet::vm_global()->oops_do 
in the same vicinity as the call to JvmtiExport::oops_do, but not all 
i.e. ZRootsIterator::oops_do and ShenandoahSerialRoots::oops_do. 
Tracking through it seems that for those GCs the VM global roots are 
processed concurrently, whereas currently JVMTI roots are not. Does that 
make any potential difference?

Thanks,
David
-----

> Thanks,
> Coleen