RFR: 8375621: Move RBTree implementation to inline file to minimize included headers [v2]

[Johan Sjölen]

On Mon, 19 Jan 2026 14:59:37 GMT, Casper Norrbin <cnorrbin at openjdk.org> wrote:

>> src/hotspot/share/utilities/rbTree.hpp line 68:
>> 
>>> 66: class outputStream;
>>> 67: class Arena;
>>> 68: class ResourceArea;
>> 
>> Brownie points if you also sort the forward declarations.
>
> The forward declarations are required by the Arena/ResourceArea allocator classes, so they would need to stay as it is currently. Since all definitions are in `rbTree.hpp`, we need to keep them for now. We could perhaps split up the various tree variants into a separate file, but I feel that would be out of scope here.

Sort as in outputStream should go after Arena because A < O in the alphabet, is what I reckon Stefan meant.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29295#discussion_r2715908545