RFR: 8343840: Rewrite the ObjectMonitor lists [v2]

[Fredrik Bredberg]

On Mon, 3 Mar 2025 23:10:29 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> Fredrik Bredberg has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update after review by David and Coleen.
>
> src/hotspot/share/runtime/objectMonitor.cpp line 1265:
> 
>> 1263:   // that updated _entry_list, so we can access w->_next.
>> 1264:   w = Atomic::load_acquire(&_entry_list);
>> 1265:   assert(w != nullptr, "invariant");
> 
> Maybe add the same assert as below for the single element case: `assert(w->TState == ObjectWaiter::TS_ENTER, "invariant")`.

Since this is not strictly necessary, I will look into this in a follow up PR.

> src/hotspot/share/runtime/objectMonitor.cpp line 1532:
> 
>> 1530:       // Let's say T1 then stalls.  T2 acquires O and calls O.notify().  The
>> 1531:       // notify() operation moves T1 from O's waitset to O's entry_list. T2 then
>> 1532:       // release the lock "O".  T2 resumes immediately after the ST of null into
> 
> Pre-existent, but this should be T1. Same in next sentence.

Fixed

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PR Review Comment: https://git.openjdk.org/jdk/pull/23421#discussion_r1981314184
PR Review Comment: https://git.openjdk.org/jdk/pull/23421#discussion_r1981313487