RFR: 8334772: Change Class::signers to an explicit field [v3]

[David Holmes]

On Thu, 18 Jul 2024 13:48:06 GMT, Chen Liang <liach at openjdk.org> wrote:

>> `Class` has 2 VM-injected fields that can be made explicit: `Object[] signers` and `ProtectionDomain protectionDomain`. We make the signers field explicit. (The ProtectionDomain can be revisited when SecurityManager is removed, as SecurityManager is accessing it via JNI as well.)
>> 
>> Migrate the JNI code to Java. The getter previously had a redundant primitive type check, which is dropped in the migrated Java code. The `Object[] getSigners` is no longer `native`, thus requiring a CSR record. Reviewers please help review the associated CSR.
>
> Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Merge branch 'master' of https://github.com/openjdk/jdk into feature/class-signers
>  - Reorder comment of classData to avoid misunderstanding
>  - 8334772: Change Class::signers to an explicit field

I am not a hprof expert but AFAICS the  `HPROF_GC_CLASS_DUMP` contains an explicit id for the classloader, signers, and pd, of the class, and then later a list of all fields declared in the class. AFAICS there is no real connection between these, so it doesn't matter if the classloader/signers/pd is an injected field, a regular Java field, or not a field at all. So in that regard it seems `signers` will now be handled the same way as `classloader` and so that should be fine.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20223#pullrequestreview-2186999675