[foreign-memaccess+abi] RFR: 8263018: Improve API for lifecycle of native resources [v2]

[Maurizio Cimadamore]

On Thu, 11 Mar 2021 09:59:23 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Ok that sounds like a good idea.
>
> Thinking more about this... thread local works fine for unbounded, not so much for bounded. I think this issue seems isolated enough that would probably better be addressed in a separate change.

I think I managed to come up with a way to solve this. As anticipated, shared unbounded allocator is now using a thread local, and just delegating allocation to the thread's confined allocator. I then removed all synchronization, except in the case of shared/bounded; I think that's acceptable (I don't think a bounded arena will really be used in a shared context).

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PR: https://git.openjdk.java.net/panama-foreign/pull/466