RFR: 8369250: Assess and remedy any unsafe usage of the Semaphore used by NonJavaThread::List [v2]

[Kim Barrett]

On Tue, 7 Oct 2025 21:23:55 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> The `NonJavaThread::List` has a statically allocated instance which contains a `SingleWriterSynchronizer`, which contains a `Semaphore`. The `VMThread` can try to remove itself from the list after the static destructors have executed, leading to an assertion failure for the `Semaphore` but potentially it could crash as the `List` itself gets deallocated..  Simplest fix is to change the `List` instance to a `DeferredStatic` such that it is never destroyed.
>> 
>> Testing:
>>  - tiers 1-3 (sanity)
>> 
>> Thanks.
>
> David Holmes has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Return class List definition to cpp file per Stefan and Kim's requests

Looks good.

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Marked as reviewed by kbarrett (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27664#pullrequestreview-3312174879