[master] RFR: OMWorld: Cleanup ObjectMonitor::_header

[Stefan Karlsson]

On Mon, 22 Apr 2024 13:20:33 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> This changes the `ObjectMonitor::_header` to `ObjectMonitor::_metadata` and cleans up the surrounding terminology. 
> 
> Parts of this could be upstreamed, but the distinction of this field between the different locking modes is introduced in OMWorld. 
> 
> This patch will conflict with Lilliput if rebased on-top of OMWorld because Lilliput introduces `static ByteSize header_offset()` which is not used after OMWorld.  They could probably be removed in both these patches.
> 
> This also changes all the fields to have the same access level (private) so that this can be a standard layout type.

src/hotspot/share/runtime/objectMonitor.hpp line 137:

> 135:   // Enforced by the assert() in metadata_addr().
> 136:   // * LM_LIGHTWEIGHT
> 137:   // Contains the _objects hashCode.

Suggestion:

  // Contains the _object's hashCode.

src/hotspot/share/runtime/objectMonitor.hpp line 146:

> 144:   // inflation. The _object does not change, so it is a good choice to share
> 145:   // its cache line with _metadata.
> 146:   DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile uintptr_t) +

Could this be using `sizeof(_metadata)` instead?

-------------

PR Review Comment: https://git.openjdk.org/lilliput/pull/161#discussion_r1576211448
PR Review Comment: https://git.openjdk.org/lilliput/pull/161#discussion_r1576220813