RFR 8231324: Shenandoah: avoid duplicated weak root works during final traversal

[Zhengyu Gu]

Updated after JDK-8231999.

Changed: heap->is_concurrent_traversal_in_progress() to 
heap->is_traversal_mode()

Webrev: http://cr.openjdk.java.net/~zgu/JDK-8231324/webrev.01/

Reran hotspot_gc_shenandoah test.

-Zhengyu


On 10/4/19 10:51 AM, Zhengyu Gu wrote:
> Please review this patch that avoids traversal GC to walk weak roots 
> twice during final traversal.
> 
> Also, it should process weak roots first, so that, fixup phase does not 
> visit dead CLDs/codes, etc.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8231324
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8231324/webrev.00/
> 
> Test:
>    hotspot_gc_shenandoah (fastdebug and release) on Linux x86_64
> 
> Thanks,
> 
> -Zhengyu