RFR: 8259962: Shenandoah: task queue statistics is inconsistent after JDK-8255019

[Zhengyu Gu]

On Tue, 19 Jan 2021 10:27:26 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> I believe `ShenandoahSTWMark` misses the TQ stats reset after the takeover from concurrent cycle. See the stack trace and events info in the bug.
> 
> Additional testing:
>  - [x] Linux x86_64, failing tests now pass
>  - [x] Linux x86_64 `hotspot_gc_shenandoah`
>  - [x]  Linux x86_64 `tier1` with Shenandoah

Thanks for catching this. Looks good.

Concurrent mark resets qstats in ShenandoahConcurrentMark::mark_stw_roots(), so it should be fine.

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Marked as reviewed by zgu (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2141