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

[David Holmes]

On Tue, 22 Oct 2024 12:31:24 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Okay but ....
>> 1. We have the current virtual thread
>> 2. We have the current carrier for that virtual thread (which is iotself a java.alng.Thread object
>> 3. We have Thread.setCurrentLockId which ... ? which thread does it update? And what does "current" refer to in the name?
>
> Thread identity switches to the carrier so Thread.currentThread() is the carrier thread and JavaThread._lock_id is the thread identifier of the carrier.  setCurrentLockId changes JavaThread._lock_id back to the virtual thread's identifier.

If the virtual thread is un-mounting from the carrier, why do we need to set the "lock id" back to the virtual thread's id? Sorry I'm finding this quite confusing.

Also `JavaThread::_lock_id` in the VM means "the java.lang.Thread thread-id to use for locking" - correct?

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1811877637