RFR: 8319137: release _object in ObjectMonitor dtor to avoid races [v3]

[Daniel D. Daugherty]

On Mon, 20 Nov 2023 17:37:15 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> Please review the following fix which moves the release of the _object WeakHandle back to the ObjectMonitor dtor. Releasing it earlier as we do today introduces a race which can lead to crashes. Tested running tiers123 in mach5.
>> 
>> This fix is an effective backout of [JDK-8256302](https://bugs.openjdk.org/browse/JDK-8256302).
>> 
>> Thanks,
>> Patricio
>
> Patricio Chilano Mateo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove redundant branches

You could do this as "[BACKOUT] JDK-8256302 releasing oopStorage when deflating allows for faster deleting"
and then merge that [BACKOUT] into the main line and resolve all conflicts. There have been quite a few follow
on changes that would have to be resolved.

That would be "cleaner" from a process POV, but I don't think it is necessary.

Please add a note to [JDK-8256302](https://bugs.openjdk.org/browse/JDK-8256302) making it clear
that fix has been effectively backed out by this fix.

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PR Comment: https://git.openjdk.org/jdk/pull/16738#issuecomment-1819529890