RFR: 8241081: Shenandoah: Do not modify update-watermark concurrently

[Aleksey Shipilev]

On 3/17/20 11:55 AM, Roman Kennke wrote:
> Webrev:
> http://cr.openjdk.java.net/~rkennke/JDK-8241081/webrev.02/

Looks good.

One tiny thing: can you please read _update_watermark into local field, assert that value and return
the same one? Instead of doing effectively three memory accesses, which might disagree.

-- 
Thanks,
-Aleksey