RFR(XS): G1: Concurrent mark stuck in loop calling os::elapsedVTime()

[Jon Masamitsu]

Per,

Are you saying that when the heap expands, "_heap_end" might not be 
updated but
"_finger" will be updated for an allocation in the newly expanded part 
of the heap?

Jon

On 4/30/2014 6:13 AM, Per Liden wrote:
> Hi,
>
> Here's another G1 concurrent mark fix I'd like to have reviewed.
>
> Summary: If the heap is expended when a concurrent mark is in progress 
> there's a window where the global marking finger (_cm->_finger) points 
> past the heap end (_cm->_heap_end). When this happens the marking 
> threads will get stuck in a loop spinning, because 
> _cm->out_of_regions() will still return false. out_of_regions() is 
> currently implemented as "return _finger == _heap_end;".
>
> This patch fixes this problem by adjusting out_of_region() to instead 
> be "return _finger >= _heap_end;". This is safe because objects in 
> those new regions will be considered live anyway, because their TAMS 
> will be equal to bottom.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8040804
> Webrev: http://cr.openjdk.java.net/~pliden/8040804/webrev.0/
>
> /Per