RFR: 8261804: Remove field _processing_is_mt, calculate it instead

[Kim Barrett]

On Wed, 24 Feb 2021 11:59:48 GMT, Leo Korinth <lkorinth at openjdk.org> wrote:

> In the reference processor, remove _processing_is_mt. Instead calculate its value in its accessor, processing_is_mt().
> 
> This change will remove some state, make RefProcMTDegreeAdjuster a bit simpler and make it much easier to derive when processing is indeed multi threaded.

Other than possibly moving the definition of `processing_is_mt()` to the .cpp file, this looks good.

src/hotspot/share/gc/shared/referenceProcessor.hpp line 417:

> 415: 
> 416:   // Whether we are in a phase when _processing_ is MT.
> 417:   bool processing_is_mt() const { return ParallelRefProcEnabled && _num_queues > 1; }

I don't think this needs to be inline, and I think moving it to the .cpp file would avoid needing to include gc_globals.hpp here.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2704