RFR: 8361300: Document exceptions for Unsafe offset methods [v4]

[Per Minborg]

On Thu, 3 Jul 2025 18:41:27 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Unsafe throws IAE for misusing static vs instance fields, and it's revealed that AtomicXxxFieldUpdaters are using this mechanism to reject static fields. This is not a good practice, but we can at least document this so we don't accidentally introduce problems.
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Test to verify observed internal unsafe behaviors

src/java.base/share/classes/java/util/concurrent/atomic/AtomicIntegerFieldUpdater.java line 405:

> 403:                 throw new IllegalArgumentException("Must be volatile type");
> 404: 
> 405:             if (Modifier.isStatic(modifiers))

Can we break out the Modifier tests in the three updater classes to a common method?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25945#discussion_r2189548142