RFR: 8321815: Shenandoah: gc state should be synchronized to java threads only once per safepoint [v4]

[William Kemper]

On Mon, 18 Dec 2023 19:28:50 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Presently, every change to the gc change is distributed to all java threads. The gc state is only changed on safepoints. For applications with a very large number of java threads this may increase time on the safepoint. It would be better to synchronize the gc state only once per safepoint.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Initialize new _gc_state_changed member.

I'll open a new PR to rename these methods and add an assert that non-java threads never touch the thread local copy of gc state.

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PR Comment: https://git.openjdk.org/jdk/pull/17112#issuecomment-1863241621