RFR: 8261473: Shenandoah: Add breakpoint suppoprt [v3]

[Aleksey Shipilev]

On Thu, 18 Feb 2021 14:06:54 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 incrementally with one additional commit since the last revision:
> 
>   Shade's comments and fixing a merge error

Marked as reviewed by shade (Reviewer).

src/hotspot/share/gc/shenandoah/shenandoahConcurrentGC.cpp line 52:

> 50: 
> 51: // Breakpoint support
> 52: class ShenandoahBreakpointScope : public StackObj {

Should probably be `ShenandoahBreakpointGCScope` to match that other "MarkScope".

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