RFR: 8340572: ConcurrentModificationException when sorting ArrayList sublists

[Stuart Marks]

On Tue, 1 Oct 2024 03:18:57 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Fixes a regression with #17818 where `ArrayList.subList(…).sort()` started incrementing `ArrayList.modCount` resulting in some cases throwing a `ConcurrentModificationException` where none was thrown before.
>> 
>> This change keeps the optimization from #17818 but restores the behavior where only sorting the `ArrayList` changes the mod count, but sorting its sublists does not.
>
> I agree with just reverting the behaviour as discussed in JBS, but will leave the actual review for the libs folk. The more general question of when to trigger CME is a very thorny one.

Right, @dholmes-ora, you might recall that we argued about this several years ago. :-) Even though I'm on the losing end of that argument, I am ok with eventually removing the modCount increments from sort and replaceAll. This is covered by JDK-8203704 which should include a spec clarification to support the change in behavior. Meanwhile, this PR should simply revert to the behavior previous to the JDK-8325679 change. (Even though that behavior is arguably wrong.)

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PR Comment: https://git.openjdk.org/jdk/pull/21250#issuecomment-2384701569