RFR (S): 7080389: G1: refactor marking code in evacuation pause copy closures

John Cuthbertson john.cuthbertson at oracle.com
Fri Aug 19 16:12:27 PDT 2011

Hi Everyone,

Hopefully this webrev 
(http://cr.openjdk.java.net/~johnc/7080389/webrev.1/) addresses 
everyones' comments.



On 08/18/11 11:17, John Cuthbertson wrote:
> Hi Everyone,
> Can I have a couple of volunteers review these refactoring changes to 
> the marking code used during evacuation pauses (both initial mark 
> pauses and regular evacuation pauses when marking is active) - the 
> change can be found at 
> http://cr.openjdk.java.net/~johnc/7080389/webrev.0/.
> The refactoring changes fix an issue that was seen with the code 
> changes for 6486945.
> During an initial mark pause, during root scanning, one thread had 
> successfully forwarded an object and had started to copy it. While the 
> object was being copied to its new location, another thread saw that 
> the object had been forwarded and, after checking that the new 
> location was unmarked, successfully marked the new location. The first 
> thread would finish the copying, see that the new location was marked 
> and skip the mark. The situation I ran into was that I was attempting 
> to obtain the size of the new object just after it was marked (by the 
> thread doing the marking) and the old object had not yet been fully 
> copied to its new location.
> With these refactoring changes, the thread that successfully forwards 
> an object in the collection set will mark the forwardee after copying 
> - allowing me to safely obtain it's size.
> Testing: several runs of the GC test suite with a marking threshold of 
> 10 and 20%, Kitchensink, and jprt.
> Thanks,
> JohnC

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