RFR (round 1), JDK-8214259: Implementation: JEP 189: Shenandoah: A Low-Pause Garbage Collector

[Kim Barrett]

> On Nov 27, 2018, at 4:46 AM, Roman Kennke <rkennke at redhat.com> wrote:
> 
> Hi Kim,
> 
>>> Sections to review (at this point) are the following:
>>> 
>>> *) shared-gc
>>>    - This is mostly boilerplate that is common to any GC
>>>    - referenceProcessor.cpp has a little change to make one assert not fail (next to CMS and G1)
>> 
>> Ick.  But I don’t have a better suggestion that doesn’t involve adding a new API
>> to CollectedHeap for use by this assertion, which seems a bit excessive if there
>> are no other uses.
> 
> Yeah.
> I guess we could add a config _discovery_is_concurrent or similar in RP,
> and check that. Or maybe one of _discovery_is_mt or _discovery_is_atomic
> already covers that? I couldn't immediately tell/100% understand their
> semantics. Seems worthy to look at after this?

It might be equivalent to _discovery_is_atomic; I don’t remember the exact
semantics right now.  I think it’s unrelated to _discovery_is_mt.

Yes, looking at this later is fine.  Please file an RFE.

>>>    - taskqueue.hpp has some small adjustments to enable subclassing
>> 
>> Why this change instead of JDK-8204947?  As the description from that RFE says:
>> "The ShenandoahTaskTerminator from the Shenandoah project is a much better implementation of a task terminator.”
> 
> Yeah, see Zhengyu's comment. Let's ignore those changes for this review
> (for now), expect our impl ported to taskqueue.hpp/cpp soon.

I’m okay with that plan.  Maybe add a comment in JDK-8204947 about this?