RFR: 8261473: Shenandoah: Add breakpoint suppoprt [v2]

[Roman Kennke]

On Wed, 10 Feb 2021 20:13:52 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> Please review this patch that adds breakpoint support for Shenandoah, that allows Shenandoah to access a few tests:
>> 
>> gc/TestConcurrentGCBreakpoints.java
>> gc/TestJNIWeak/TestJNIWeak.java
>> gc/TestReferenceClearDuringMarking.java
>> gc/TestReferenceClearDuringReferenceProcessing.java
>> gc/TestReferenceRefersTo.java
>> 
>> The drawback is that above tests can not run with passive mode, which can result tests to hang, as breakpoints only apply to concurrent GC.
>> 
>> Test:
>> - [x] hotspot_gc_shenandoah
>> - [x] tier1 with Shenandoah
>
> Zhengyu Gu has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:
> 
>  - Merge
>  - update
>  - init update

The change looks good to me, thanks!

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Marked as reviewed by rkennke (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2489