RFR: 8258742: Move PtrQueue reset to PtrQueueSet subclasses

[Kim Barrett]

On Mon, 18 Jan 2021 10:35:14 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Please review this change to the PtrQueue hierarchy, changing queue reset
>> from an intrinsic operation of the queue to an operation the qset performs
>> on a queue.  This is another piece of the refactoring being done under
>> JDK-8258251, separated out for easier review.
>> 
>> After the refactoring of queue reset, PtrQueue::is_empty and PtrQueue::size
>> are no longer used, so are removed.  Further, PtrQueue::{set_}index_in_bytes
>> are removed, directly using _index instead.
>> 
>> A less obvious part of the change is in the G1 remark task and Shenandoah
>> final marking task.  The threads walk performed by these no longer directly
>> processes the partial per-thread SATB buffers.  Instead they just flush the
>> queues for later completed buffer processing.
>> 
>> Testing:
>> mach5 tier1
>> local (linux-x64) hotspot:tier1 with -XX:+UseShenandoahGC
>
> Lgtm.

Thanks @tschatzl and @walulyai for reviews.

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PR: https://git.openjdk.java.net/jdk/pull/2115