RFR: 8359924: Deprecate and obsolete ParallelRefProcEnabled

[Kim Barrett]

On Wed, 18 Jun 2025 14:47:13 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> 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.

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PR Comment: https://git.openjdk.org/jdk/pull/25875#issuecomment-2985742153