RFR: JDK-8148992: VM can hang on exit if root region scanning is initiated but not executed

[Thomas Schatzl]

Hi Bengt,

On Wed, 2016-02-10 at 10:02 +0100, Bengt Rutisson wrote:
> Hi Jesper (and everyone),
> 
> On 2016-02-08 15:50, Jesper Wilhelmsson wrote:
> > Looks good!
> 
> Thanks for looking at this!
> 
> I found a bug in the last webrev. The 
> G1ConcurrentMark::scanRootRegions()  has the side effect that it 
> calls ClassLoaderDataGraph::clear_claimed_marks(). It is not ok to 
> skip this call just because there are no root regions to scan. So, I 
> can't guard the call to scanRootRegions() with "if
> (_cm->root_regions()->scan_in_progress())" as I did in webrev.02.
> 
> I find this side effect a bit odd. So, I moved 
> ClassLoaderDataGraph::clear_claimed_marks() out to its own phase. 
> This will also make it show up clearer in our logs if it starts 
> taking a long time.

I think this is a good idea.

> 
> Instead of checking scan_in_progress() both before the call to 
> scanRootRegions() and inside of it I moved the assert(!has_aborted()) 
> in to scanRootRegions().
> 
> Here's an updated webrev:
> http://cr.openjdk.java.net/~brutisso/8148992/webrev.03/
> 
> And here's a diff compared to the last version:
> http://cr.openjdk.java.net/~brutisso/8148992/webrev.02-03.diff/

Looks good.

One nit: the change in heapVerifier.cpp seems to be something
completely unrelated. Do you think it would be a good idea to move it
to some extra CR?

 411     _g1h->print_extended_on(log.error_stream());

Would not need a re-review for this.

Thanks,
  Thomas