RFR: 8324983: race in CompileBroker::possibly_add_compiler_threads [v2]

[Doug Simon]

On Thu, 1 Feb 2024 17:37:28 GMT, Tom Rodriguez <never at openjdk.org> wrote:

>> The number of active compiler threads is decremented before the compiler thread has actually activated so possibly_add_compiler_thread might start a new thread on the existing JavaThread.  This adds a check that it's really exiting before proceeding and some new guarantees that ensure threads aren't started on top running threads.
>
> Tom Rodriguez has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Convert guarantee to assert

Marked as reviewed by dnsimon (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17662#pullrequestreview-1857207940