RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning

[Patricio Chilano Mateo]

On Mon, 28 Oct 2024 00:29:25 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> I was wondering what this was too but the _previous_owner_tid is the os thread id, not the Java thread id.
>> 
>> 
>> $ grep -r JFR_THREAD_ID
>> jfr/support/jfrThreadId.hpp:#define JFR_THREAD_ID(thread) (JfrThreadLocal::external_thread_id(thread))
>> jfr/support/jfrThreadId.hpp:#define JFR_THREAD_ID(thread) ((traceid)(thread)->osthread()->thread_id())
>> runtime/objectMonitor.cpp:    _previous_owner_tid = JFR_THREAD_ID(current);
>> runtime/objectMonitor.cpp:    iterator->_notifier_tid = JFR_THREAD_ID(current);
>> runtime/vmThread.cpp:  event->set_caller(JFR_THREAD_ID(op->calling_thread()));
>
> Then it looks like the JFR code needs updating as well, otherwise it is going to be reporting inconsistent information when virtual threads are locking monitors.

So we use the os thread id when INCLUDE_JFR is not defined, but in that case we never actually post JFR events. So these _previous_owner_tid/_notifier_tid will be unused.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1831592617