RFR: 8255527: Shenandoah: Let ShenadoahGCStateResetter disable barriers

[Aleksey Shipilev]

On Wed, 28 Oct 2020 10:43:07 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> JDK-8255036 introduced a regression: the new ShenandoahGCStateResetter does not actually disable barriers: it only records old state (without changing it) and then restores that state (i.e a no-op). 
> 
> Testing: hotspot_gc_shenandoah (also on conc-weakref branch, where the bug did manifest)

Minor nit, otherwise looks good.

src/hotspot/share/gc/shenandoah/shenandoahRootVerifier.cpp line 46:

> 44:   _gc_state(ShenandoahHeap::heap()->gc_state()),
> 45:   _concurrent_weak_root_in_progress(ShenandoahHeap::heap()->is_concurrent_weak_root_in_progress()) {
> 46:   ShenandoahHeap* heap = ShenandoahHeap::heap();

L52 below has `ShenandoahHeap* const heap`, should be here as well, at least for consistency?

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/899