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

[Roman Kennke]

Looks good. (I was pretty sure I looked through it yesterday already. Hmm.)

Thanks,
Roman

> 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
>