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.

Wow! Okay I'm no longer considering this to be a trivial fix. I'll update the description
in a second...

@dholmes-ora, @fisk, @robehn and @zhengyu123 - Thanks for chiming in on this
review. Obviously it will take me a bit of time to navigate this variety of comments
and figure out a way forward. 

On the plus side, My Mach5 Tier8 is down to 11 of the usual 48 24H tasks and so
far there are no failures. So the testing on this fix (JDK-8288497) and JDK-8288139
is look just dandy!

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