RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning [v11]

[Alan Bateman]

On Fri, 25 Oct 2024 22:09:30 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:
>> 
>>  - Add/fix comments for David
>>  - Move condition to new line in nmethod::preserve_callee_argument_oops
>
> test/jdk/java/lang/reflect/callerCache/ReflectionCallerCacheTest.java line 30:
> 
>> 28:  *         by reflection API
>> 29:  * @library /test/lib/
>> 30:  * @requires vm.compMode != "Xcomp"
> 
> If there is a problem with this test running with -Xcomp and virtual threads, maybe it should be handled as a separate bug fix.

JBS has several issues related to ReflectionCallerCacheTest.java and -Xcomp, going back several releases. It seems some nmethod is keeping objects alive and is preventing class unloading in this test. The refactoring of j.l.ref in JDK 19 to workaround pinning issues made it go away. There is some minimal revert in this PR to deal with the potential for preemption when polling a reference queue and it seems the changes to this Java code have brought back the issue. So it's excluded from -Xcomp again.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1817692430