RFR: 8351565: Implement JEP 502: Stable Values (Preview)

[Per Minborg]

On Wed, 12 Mar 2025 14:14:59 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> You can probably use `acquire` only for the first `get` as it is in the fast path. For other I guess `volatile` is fine.
>
> Yeah. Maybe that could strike a balance.

On an M1 Mac:

Volatile:


StableValueBenchmark.stable        avgt   10  1.373 ? 0.057  ns/op
StableValueBenchmark.stableNull    avgt   10  1.245 ? 0.074  ns/op


Acquire:


StableValueBenchmark.stable        avgt   10  1.339 ? 0.044  ns/op
StableValueBenchmark.stableNull    avgt   10  1.241 ? 0.090  ns/op


We would have to examine the difference on other platforms as well.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23972#discussion_r1993284760