RFR: 8166607: G1 needs klass_or_null_acquire

[Kim Barrett]

> On Nov 15, 2016, at 5:21 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi Kim,
> 
> On Mon, 2016-11-07 at 14:38 -0500, Kim Barrett wrote:
>>> 
>>> On Nov 7, 2016, at 5:53 AM, Thomas Schatzl <thomas.schatzl at oracle.c
>>> om> wrote:
>>> Maybe it would be cleaner to call a method in the barrier set
>>> instead of inlining the dirtying + enqueuing in lines 685 to 691?
>>> Maybe as an additional RFE.
>> We could use _ct_bs->invalidate(dirtyRegion).  That's rather
>> overgeneralized and inefficient for this situation, but this
>> situation should occur *very* rarely; it requires a stale card get
>> processed just as a humongous object is in the midst of being
>> allocated in the same region.
> 
> I kind of think for these reasons we should use _ct_bs->invalidate() as
> it seems clearer to me. There is the mentioned drawback of having no
> other more efficient way, so I will let you decide about this.

I've made the change to call invalidate, and also updated some comments.

CR:
https://bugs.openjdk.java.net/browse/JDK-8166607

Webrevs:
full: http://cr.openjdk.java.net/~kbarrett/8166607/webrev.03/
incr: http://cr.openjdk.java.net/~kbarrett/8166607/webrev.03.inc/

Also, see RFR: 8166811, where I've included a webrev combining the
latest changes for 8166607 and 8166811, since they are rather
intertwined.  I think I'll do as Erik suggested and push the two
together.