RFR: 8365932: Implementation of JEP 516: Ahead-of-Time Object Caching with Any GC [v10]

[Erik Österlund]

On Mon, 27 Oct 2025 17:54:37 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Erik Österlund has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 22 commits:
>> 
>>  - Merge branch 'master' into 8326035_JEP_object_streaming_v6
>>  - Missing unlock diagnostic VM options, and remove unintended comment
>>  - Fix for minimal
>>  - Change streaming/mapping states to be binary instead of tri states
>>  - Clean up VMProps
>>  - Make AOTStreamableObjects diagnostic
>>  - Test polishing
>>  - Merge branch 'master' into 8326035_JEP_object_streaming_v6
>>  - Test fix
>>  - move exception marks outside locks
>>  - ... and 12 more: https://git.openjdk.org/jdk/compare/97e5ac6e...3d771ca2
>
> src/hotspot/share/cds/aotThread.hpp line 33:
> 
>> 31: // A hidden from external view JavaThread for materializing archived objects
>> 32: 
>> 33: class AOTThread : public JavaThread {
> 
> Short names are good but this one don't provide any information about what it does.
> How about `AOTHeapLoadingThread`?

I was sort of thinking that there might be more AOT cache work that could benefit from concurrency, other than object loading. That's why I named it a bit more generically. Does that make sense? Otherwise, I'm open to renaming it.

> src/hotspot/share/jfr/support/jfrThreadLocal.cpp line 483:
> 
>> 481:   assert(t != nullptr, "invariant");
>> 482:   oop threadObj = t->threadObj();
>> 483:   return threadObj != nullptr ? AccessThreadTraceId::id(threadObj) : static_cast<traceid>(t->monitor_owner_id());
> 
> Is this related to JEP?
> Is it bug fix (return `monitor_owner_id` instead of 0)?

I added this because the AOT thread starts earlier than the Thread class is initialized. Therefore, I have to create the thread with a null thread object, and initialize the thread oop after the Thread class is initialized. This threw this JFR code off. So I made it accept the monitor_owner_id which is set up for similar reasons.

> src/hotspot/share/memory/metaspace.cpp line 29:
> 
>> 27: #include "cds/aotMetaspace.hpp"
>> 28: #include "cds/cdsConfig.hpp"
>> 29: #include "cds/heapShared.hpp"
> 
> There are no other changes in this file. Is this include needed?

Probably not - I'll remove it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27732#discussion_r2468536258
PR Review Comment: https://git.openjdk.org/jdk/pull/27732#discussion_r2468546194
PR Review Comment: https://git.openjdk.org/jdk/pull/27732#discussion_r2468547745