RFR: 8258254: Move PtrQueue flush to PtrQueueSet subclasses

[Aleksey Shipilev]

On Sun, 20 Dec 2020 10:03:15 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to the PtrQueue hierarchy, changing queue flushing
> from an intrinsic operation of the queue to an operation the qset performs on
> a queue.  This is a piece of the refactoring being done under JDK-8258251,
> separated out for easier review.
> 
> This change also removes a couple of no longer used internal helper functions
> from PtrQueue.
> 
> Testing:
> mach5 tier1
> local (linux-x64) hotspot:tier1 with -XX:+UseShenandoahGC

Shenandoah and shared parts look fine.

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1851