RFR: 8298601: Refactor archiving of java.lang.Module objects [v2]

[Calvin Cheung]

On Thu, 22 Dec 2022 21:50:01 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> This RFE is a prerequisite for [JDK-8296344: Remove dependency on G1 for writing the CDS archive heap](https://bugs.openjdk.org/browse/JDK-8296344). 
>> 
>> The main change of this RFE is in `HeapShared::archive_reachable_objects_from()`. We avoid the use of "archived objects" in the interface between CDS and the module system, and use integer "root indices" instead. (See note [1] in [JDK-8298600](https://bugs.openjdk.org/browse/JDK-8298600).)
>> 
>> Also, for better encapsulation, the module-specific code has been moved from `HeapShared::check_module_oop()` to the three new functions in modules.cpp.
>> 
>> ----
>> 
>> Besides the refactoring, this RFE also tightens up the code that deals with `java.lang.Module` oops and the corresponding C++ `ModuleEntry` objects.
>> 
>> As this is admittedly an obscured area of the CDS archive heap, I've added the following:
>> 
>> - Assertions to make sure that when an oop is archived, the corresponding C++ object is also archived, and vice-versa.
>> - More comments
>
> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review from @coleenp and @calvinccheung

Updates look good. Thanks.

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Marked as reviewed by ccheung (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11715