RFR: 8320318: ObjectMonitor Responsible thread [v4]

[David Holmes]

On Sun, 29 Sep 2024 07:17:32 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> I see where it came from in the aarch64 code, and that code does a stlr() to satisfy the JMM.  It's fine.  Leave it.
>
> To get the correct semantics for the JMM the releasing of a monitor has to have release semantics (funny that!). So setting the owner to null should be a release_store. On some platforms we get "release" semantics for free.
> 
> The fence is needed for correct operation of our own locking implementation and has nothing to do with JMM.

But I concede that the comment is less clear on platforms where the release does not appear in the instruction stream. But I think it important that the need for release semantics be documented.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19454#discussion_r1779942129