RFR: 8258239: Shenandoah: Used wrong closure to mark concurrent roots

[Roman Kennke]

On Mon, 14 Dec 2020 15:20:42 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> During concurrent mark phase, there should not have forwarded objects. Therefore, it should use ShenandoahMarkRefsClosure to mark concurrent roots, instead of ShenandoahMarkResolveRefsClosure.
> 
> Note: this is *not* a correctness bug, but performance one, as ShenandoahMarkResolveRefsClosure closure unnecessarily resolves forwarding pointers, where always resolved to themselves.
> 
> - [x] hotspot_gc_shenandoah

Looks good to me!

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Marked as reviewed by rkennke (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1768