8359924: Deprecate and obsolete ParallelRefProcEnabled

[albertnetymk]

Deprecating ParallelRefProcEnabled, which is used only by Parallel and G1, and both have it enabled by default via:

  if (FLAG_IS_DEFAULT(ParallelRefProcEnabled) && ParallelGCThreads > 1) {
    FLAG_SET_DEFAULT(ParallelRefProcEnabled, true);
  }

Disabling it offers little benefit and its presence incurs some implementation complexity in the reference-processor.

---

Progress

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• Change requires CSR request JDK-8359925 to be approved

Issues

• JDK-8359924: Deprecate and obsolete ParallelRefProcEnabled (Enhancement - P4)
• JDK-8359925: Deprecate and obsolete ParallelRefProcEnabled (CSR)

Reviewers

• Thomas Schatzl (@tschatzl - Reviewer)
• Kim Barrett (@kimbarrett - Reviewer)
• David Holmes (@dholmes-ora - Reviewer)

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8359924: Deprecate and obsolete ParallelRefProcEnabled

Reviewed-by: tschatzl, kbarrett, dholmes

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At the time when this comment was updated there had been 28 new commits pushed to the master branch:

• d627282: 8360143: ProblemList runtime/NMT/VirtualAllocTestType.java
• 96f71a9: 8255082: HotSpot Style Guide should permit noexcept
• 17cf497: 8357550: GenShen crashes during freeze: assert(!chunk->requires_barriers()) failed
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[albertnetymk]

/cc hotspot-gc

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Webrevs

• 00: Full (01c1bf67)

[tschatzl]

I'm wondering whether we should make ParallelRefProcBalancingEnabled diagnostic at the same time? (Separately).

Same with ReferencesPerThread, again separately, but that does not need a CSR.

[kimbarrett]

Looks good.

[kimbarrett]

I'm wondering whether we should make ParallelRefProcBalancingEnabled diagnostic at the same time? (Separately).

I think it's too late for that. We can only deprecate a product option in the current release, we can't change it
to diagnostic (which is removing it from being available for normal usage). We could deprecate now with the
intent of going to diagnostic rather than removal, but I'd rather we just deprecate for removal, and remove
in the next release.

Same with ReferencesPerThread, again separately, but that does not need a CSR.

We could remove ReferencesPerThread immediately, without first deprecating, since it's experimental.

[dholmes-ora]

LGTM!

Thanks