RFR(XS): make shared variables volatile

[Roman Kennke]

Am Donnerstag, den 22.09.2016, 16:29 +0100 schrieb Andrew Haley:
> On 22/09/16 16:07, Roman Kennke wrote:
> > 
> > The question that came up while discussing this is how to access
> > such
> > fields. Atomic and OrderAccess both have no public load() and
> > store()
> > methods (or similar). There is load_acquire() and release_store()
> > both
> > those are recommended only to be used in pairs. I believe it would
> > have
> > the desired effects, but doesn't exactly look clean. Any hints?
> 
> acquire and release are exactly what you want.  Whether you do this
> with fences or load_acquire() and release_store() does not affect
> correctness.  If you see an acquire without a matching release or
> vice
> versa that's probably a bug.

Yes. But what if modification is done by, e.g., Atomic::inc() and in
some other place you want to read the value? I can use load_acquire()
and it would (probably?) be the right thing, but has no matching
release_store(). That's what we were wondering if the API should
provide OrderAccess::load() or something similar.

Roman