RFR: 8343840: Rewrite the ObjectMonitor lists [v2]

[David Holmes]

On Mon, 3 Mar 2025 23:15:46 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 204:
> 
>> 202: //   If the thread (F) that removes itself from the end of the list
>> 203: //   hasn't got any prev pointer, we just set the tail pointer to
>> 204: //   null, see 5) and 6) below.
> 
> Setting the tail pointer to null would be for the case when this node is also the head, i.e single element. Otherwise we just rebuild the doubly link list, unlink F, and set entry_list_tail to G. In other words, the comment here and below seems to be missing that we have to build the doubly link list when F acquires the monitor, not when F needs to find a successor.

We don't rebuild at this point. The thread that is removing itself just sets tail to null if there is no prev. Later when F exits the monitor it will construct the DLL to find the next successor.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23421#discussion_r1978608595