RFR: 8258255: Move PtrQueue active flag to SATBMarkQueue

[Thomas Schatzl]

On Thu, 17 Dec 2020 13:17:11 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to the PtrQueue hierarchy, moving the support for
> "active" queues and qset to SATBMarkQueue[Set], which is the only user of
> this feature.  Other classes derived from PtrQueue[Set] currently work
> around or ignore this feature.  This change removes it from consideration
> entirely for those other classes.
> 
> Testing:
> mach5 tier1
> local (linux-x64) hotspot:tier1 with -XX:+UseShenandoahGC
> 
> In the process of doing this refactoring I noticed that some of the
> vmStructs support around PtrQueue[Set] didn't get moved from G1 to shared,
> and the G1 parts are incomplete.  Filed JDK-8258581 to address that.

Apart from that request with the comment, lgtm.

src/hotspot/share/gc/shared/satbMarkQueue.hpp line 106:

> 104:   size_t _process_completed_buffers_threshold;
> 105:   size_t _buffer_enqueue_threshold;
> 106:   // SATB is only active during marking.  Enqueuing is not done when inactive.

I would prefer to avoid the double-negation in the second sentence.

src/hotspot/share/gc/shared/satbMarkQueue.hpp line 155:

> 153:   // When active, add obj to queue by calling enqueue_known_active.
> 154:   void enqueue(SATBMarkQueue& queue, oop obj) {
> 155:     if (queue.is_active()) enqueue_known_active(queue, obj);

Maybe something for a different CR and probably pre-existing: `enqueue()` in some contexts is already called with `queue.is_active() == true`. I.e. this check is superfluous, particularly when called for object arrays.

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Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1820