RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning [v12]

[Richard Reingruber]

On Sat, 26 Oct 2024 01:54:26 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Patricio Chilano Mateo has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Restore use of atPointA in test StopThreadTest.java
>>  - remove interruptible check from conditional in Object::wait
>
> src/hotspot/cpu/x86/stubGenerator_x86_64.cpp line 3796:
> 
>> 3794:   __ movbool(rscratch1, Address(r15_thread, JavaThread::preemption_cancelled_offset()));
>> 3795:   __ testbool(rscratch1);
>> 3796:   __ jcc(Assembler::notZero, preemption_cancelled);
> 
> If preemption was canceled, then I wouldn't expect patch_return_pc_with_preempt_stub() to get called.  Does this mean preemption can get canceled (asynchronously be a different thread?) even afgter patch_return_pc_with_preempt_stub() is called?

The comment at the `preemption_cancelled` label explains that a second attempt to acquire the monitor succeeded after freezing. The vthread has to continue execution. For that its frames (removed just above) need to be thawed again.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1817703994