RFR: 8345314: Add a red–black tree as a utility data structure [v14]

[Gerard Ziemski]

On Mon, 20 Jan 2025 15:03:06 GMT, Casper Norrbin <cnorrbin at openjdk.org> wrote:

>> Hi everyone,
>> 
>> This effort began as an exploration of replacing the current NMT treap with a red-black tree. Along the way, I discovered that others were also interested in having a general-purpose tree structure available within HotSpot.
>> 
>> The red-black tree is designed to serve as a drop-in replacement for the existing NMT treap, keeping a nearly identical interface. However, I’ve also added a few additional requested features, such as an iterator.
>> 
>> Testing builds off the treap tests, adding a few extra that inserts/removes and checks that the tree is correct. Testing uses the function `verify_self`, which iterates over the tree and checks that all red-black tree properties hold. Additionally, the tree has been tested in vmatree instead of the treap without any errors.
>> 
>> For those who may want to revisit the fundamentals of red-black trees, [Wikipedia](https://en.wikipedia.org/wiki/Red%E2%80%93black_tree) offers a great summary with tables covering the various balancing cases. Alternatively, your favorite data structure book could provide even more insight.
>
> Casper Norrbin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   const functions

Nitpick: everywhere else in our code we refer to the tag parameter as `mem_tag`, not `mt`. I'm not 100% sure whether this needs to be pointed out, but I think I'd prefer if we remained consistent and used `mem_tag`.

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PR Review: https://git.openjdk.org/jdk/pull/22360#pullrequestreview-2565595412