RFR: 8288497: add support for JavaThread::is_oop_safe() [v3]

[Daniel D. Daugherty]

On Fri, 17 Jun 2022 01:01:52 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> The logic style of this function is a carry over from before we had Thread-SMR
>> and we tried to detect a freed JavaThread. With Thread-SMR, we don't need to
>> do the check this way at all.
>> 
>> Do we really want to change that as part of this fix for JDK19?
>
> No it can be cleaned up later. This fix just highlighted the badness of that piece of code. :)

New RFE filed:

[JDK-8289003](https://bugs.openjdk.org/browse/JDK-8289003) JavaThread::check_is_terminated() implementation should rely on Thread-SMR

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