RFR(XS): make shared variables volatile

[Aleksey Shipilev]

On 09/21/2016 04:40 PM, Zhengyu Gu wrote:
> http://cr.openjdk.java.net/~zgu/volatile/webrev.01/

+1

I wonder if this means we should update/poll these volatile variables
with Atomic::* too, at least for the benefit of weak arches like AArch64.

Thanks,
-Aleksey