RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning [v8]

[Alan Bateman]

On Thu, 24 Oct 2024 05:54:11 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Patricio Chilano Mateo has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Fix comment in objectMonitor.hpp and javaThread.hpp
>>  - Skip printing tid when not available
>
> src/hotspot/share/prims/jvm.cpp line 4012:
> 
>> 4010:     }
>> 4011:     ThreadBlockInVM tbivm(THREAD);
>> 4012:     parkEvent->park();
> 
> What code does the unpark to wake this thread up? I can't quite see how this unparker thread operates as its logic seems dispersed.

It's very similar to the "Reference Handler" thread. That thread calls into the VM to get the pending-Reference list. Now we have "VirtualThread-unblocker" calling into the VM to get the list of virtual threads to unblock. ObjectMonitor::ExitEpilog will the unpark this thread when the virtual thread successor is on the list to unblock.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1814450822