[lworld] RFR: 8377451: [lworld] Add ValuePayload abstraction [v15]
Axel Boldt-Christmas
aboldtch at openjdk.org
Wed Feb 18 14:06:52 UTC 2026
> Create a wrapper class which represents the payload of an InlineKlass object.
>
> The current convention is to use a `void*` representing where the payload starts, the `InlineKlass*` (as we do not always have a header when flattened) and a `LayoutKind` (describing the payloads layout).
>
> I suggest we introduce something like a `ValuePayload` which encapsulate these properties. As well as a hierarchy built upon these, with the proper interfaces implemented.
> * ValuePayload (Any payload)
> * ~RawValuePayload (Payload with holder erased)~ (Removed in favour of using a static function)
> * BufferedValuePayload (Payload of normal heap object)
> * FlatValuePayload (Payload of flattened value)
> * FlatFieldPayload (Payload of flattened field)
> * FlatArrayPayload (Payload of flattened array element)
>
> The goal is to both make interfaces clearer, and easier to understand. As well as consolidating the implementation in one place rather than spread across different subsystems.
>
> Each type (except RawValuePayload) also allows for the creation of a Handle, (thread local, or in an OopStorage) for keeping the payload as a thread or global root.
>
> The ValuePayload class is also the interface for interacting with the Access API for InlineKlass objects.
>
> * Testing
> * Running tier 1-4 with preview enabled
> * Running app tests with preview enabled
> * Running normal tier 1-5
>
> #### _Extra Notes:_
> * The `OopHandle` type is there so that we can migrate the JVMTI payload abstraction implementation to using this instead. (Future RFE)
> * Some interfaces got cleaned up. Some are unused. Like the `null_payload` which was superseded by the `Access::value_store_null`. C1 still uses the `.null_reset` but if that dependency is removed we should be able to remove that weird object all together.
> * Simply adding the Java to VM transition deep inside the payload code created a circular include dependency here. So rather than fixing that, I implemented the relevant bytecodes in the BytecodeInterpreter.
Axel Boldt-Christmas has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 73 commits:
- Merge remote-tracking branch 'upstream_valhalla/lworld' into lworld-payload-rebase
- Merge remote-tracking branch 'upstream_valhalla/lworld' into lworld-payload-rebase
- Destructor is a CHECK_UNHANDLED_OOPS property
- @shipilev formatted table
- Revert "Fix BytecodeInterpreter dispatch table"
This reverts commit 59c1fc2e7dedd079a61dced4401267dace7c642d.
- Revert "Avoid having to align label entires"
This reverts commit 342cd358eec59e1798ef62d03bbbd3a0e0f79d9d.
- Missed header guard rename
- Rename inlineKlassPayload files to valuePayload
- Add missing inline keywords
- Fix typo in suggested fix
- ... and 63 more: https://git.openjdk.org/valhalla/compare/c27e815e...90d0990a
-------------
Changes: https://git.openjdk.org/valhalla/pull/2068/files
Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2068&range=14
Stats: 2211 lines in 39 files changed: 1806 ins; 237 del; 168 mod
Patch: https://git.openjdk.org/valhalla/pull/2068.diff
Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2068/head:pull/2068
PR: https://git.openjdk.org/valhalla/pull/2068
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