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

Bengt Rutisson bengt.rutisson at oracle.com
Sun Aug 21 14:03:32 PDT 2011

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!

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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