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

[Chen Liang]

On Wed, 30 Jul 2025 17:32:57 GMT, John R Rose <jrose at openjdk.org> wrote:

>> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Test to verify observed internal unsafe behaviors
>
> src/hotspot/share/prims/unsafe.cpp line 496:
> 
>> 494:     Symbol *name = fs.name();
>> 495:     if (name->equals(utf_name)) {
>> 496:       offset = fs.offset();
> 
> While you are here, if you keep this check, rename this particular function `find_field_offset` to `find_nonstatic_field_offset` (not the other one that takes the "must be static" flag).
> 
> The logic, as written, is difficult to understand because of the behavioral difference between the two overloading.
> 
> (I note that "instance field" is also a term of art in our code base, but "nonstatic_field" is more common.)
> 
> Alternatively, and probably better, take out this particular check (restoring equal access to static and non-static) and just rely on the checks in Java code.  Such checks are almost always better (easier to reason about by humans and JITs) than checks in C++ code.

This particular method intentionally avoids accessing Java reflective objects to reduce startup overhead. I think a better approach may be returning error code and have Java code report a failure. Thoughts?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25945#discussion_r2245996580