RFR: 8288497: add support for JavaThread::is_gc_barrier_detached()

[Daniel D.Daugherty]

On Wed, 15 Jun 2022 15:44:21 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

> A trivial fix to add support for JavaThread::is_gc_barrier_detached() which allows
> us to add checks to detect failures like:
> 
>     JDK-8288139 JavaThread touches oop after GC barrier is detached
>     https://bugs.openjdk.org/browse/JDK-8288139
> 
> This fix along with the fix for JDK-8288139 has been tested in Mach5 Tier[1-8].
> There are no related failures in Mach5 Tier[1-7]; Mach5 Tier8 is still running.

If the folks that own the barrier code add detection checks there, then this code
can be removed in the future. For now, I would like to get this code in so that I
can continue to search for additional instances of this type of failure.

As for the addition of the _thread_gc_barrier_detached TerminatedTypes value
and the location of when that state goes active, it is that new state and it's
placement that verified that the code in ThreadsSMRSupport::remove_thread()
was in the wrong place (fixed in JDK-8288139). Depending on the
_thread_terminated TerminatedTypes value did not and would not have verified
that problem.

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PR: https://git.openjdk.org/jdk19/pull/20