RFR: 8338566: Missing membar in ciEnv::get_or_create_exception before publishing handle

[David Holmes]

On Wed, 11 Sep 2024 14:17:30 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> Similar to [JDK-8251923](https://bugs.openjdk.org/browse/JDK-8251923), we need a store-store barrier before publishing a handle because otherwise another thread could observe the handle before it's fully initialized and read null from it. This affects architectures with a weak memory model like AArch64.
> 
> Unfortunately, this only happened twice in our testing and I was never able to reproduce it.
> 
> Thanks,
> Tobias

Safe publication is the responsibility of the publisher, so this PR seems fine to me in that regard. I don't think `make_global` should end in a storestore!

But is this storestore sufficient to make this publication scenario perfectly thread-safe? I would have expected to see a release_store/load_acquire pairing in the ` ciEnv::*Exception_instance()` methods.

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PR Comment: https://git.openjdk.org/jdk/pull/20950#issuecomment-2344679325