[crac] RFR: Prevent concurrent cleanup by cleaner thread and checkpoint notifications

[Radim Vansa]

On Tue, 30 May 2023 12:43:44 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> I don't follow. PhantomCleanableRefs are cleaned strictly after this point (these have later priority), other cleaners will be queued up by GC but not called until restore.
>
> I mean, once we synchronized cleaner thread from picking up PhantomCleanableRefs, there is apparently no reason to go to the next priority and discover cleanups through registrations in the CRaC -- instead, all cleanups are discoverable thorugh the list maintained by the cleaner. It seems we can go through the list right from this Resource and run cleanups.

Alright, you mean that PCRs won't be Resources anymore and we'll clean them up whether are these already in the `queue` or not, without waiting for the GC to move them into that.

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PR Review Comment: https://git.openjdk.org/crac/pull/73#discussion_r1211258883