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

John Cuthbertson john.cuthbertson at oracle.com
Mon Aug 22 15:12:50 PDT 2011

Hi Bengt, Tony, Stefan,

Thanks again for the review comments. I have to hold off pushing this as 
I have seen a failure while doing a sanity check after merging the 
workspace. So until I get to the bottom of the failure - consider this 
as "on hold".



On 08/21/11 14:03, Bengt Rutisson wrote:
> Hi John,
> This new webrev looks good to me.
> The discussion that Stefan and Tony had was good. I like the new 
> template parameter name (do_mark_object) and the new comments much 
> better. In fact, I realize my initial comments regarding those were a 
> bit wrong since I had misinterpreted the code due to the old comments. 
> Thanks for finding a good solution to this.
> Ship it!
> Bengt
> On 2011-08-20 01:12, John Cuthbertson wrote:
>> Hi Everyone,
>> Hopefully this webrev 
>> (http://cr.openjdk.java.net/~johnc/7080389/webrev.1/) addresses 
>> everyones' comments.
>> Thanks,
>> JohnC
>> 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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