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

[Aleksey Shipilev]

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

It looks to me the issue is not exactly in CI, but in the fact that we can publish a racily constructed global JNI handle. If so, shouldn't we be adding `storestore` at the exit path in `JNIHandles::make_global` to be absolutely sure we covered all uses like these?

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PR Review: https://git.openjdk.org/jdk/pull/20950#pullrequestreview-2297315445