RFR: Scan remembered [v2]

[Kelvin Nilsen]

On Wed, 13 Jan 2021 13:49:41 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Improvements requested during initial review
>>   
>>   These changes are cosmetic and/or related to comments.
>
> src/hotspot/share/gc/shenandoah/shenandoahHeap.inline.hpp line 323:
> 
>> 321:     // Increment age in young copies.
>> 322:     if (target_gen == YOUNG_GENERATION) {
>> 323:       copy_val->incr_age();
> 
> I am not sure incr_age() work with concurrent version. e.g. if the object has displaced mark and two threads try to evacuate the object, both will increase age on displaced mark word.

We did discover the need to deal with displaced mark words and a subsequent commit replaces the call to incr_age() with a call to a newly introduced incrase_object_age() function which includes special handling for displaced mark words.

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PR: https://git.openjdk.java.net/shenandoah/pull/12