Diposables and PluginDataHolders

[CubBossa]

Is your feature request related to a problem?

Not really, rather general code style

Describe the solution you'd like.

When working on a Jetbrains plugin I was positively surprised about how nice the plugin system works. I came across two patterns that I would love to use in Minecraft development and wanted to throw them in as ideas here.

Disposables:
A simple interface like Closable and AutoClosable, offering a void dispose() method. The dispose method is not similar to a destructor but declares the end of usage of an object. A constructor invocation and the dispose() invocation frame the lifetime of the object unrelated to the garbage collection and referencing or anything.
In combination with a Disposer instance, Disposables can be put into relation. For example, Plugin would extend Disposable and whenever I create any lasting object within my plugin (classes like ScoreboardHandler, PlayerDataHandler, ...) I would let them implement Disposable and bind them to my plugin with

Disposer.get().register(this, myPlugin);

in the constructor.

If a plugin for whatever reasons disables, all its resources would be disposed by evaluating the relations in the Disposer instance.
A very common situation is that a plugin constructor needs to set up many different manager classes, which may want to be closed in onDisable().
If any step in onEnable() fails, onDisable() would be likely to create NullpointerExceptions and therefore have issues while disabling too.
With the disposable system, resources would be freed only if they have been claimed first and there would no need to reference them in the onDisable hook.
Another feature of it: Your own plugin could be linked to another plugin, so for example whenever Vault gets disabled, your plugin would be disposed through the linkage in the Disposer and disable itself too, if it relies on Vault. The lifespan of your plugin would be bound to its dependencies and if any fails, your plugin would not work properly and therefore disables too.

PluginDataHolder:
Another thing Jetbrains does is implement an Interface to hold keys and values, similar to the Pointered class from adventure. They implement it with File objects, AST nodes, Editors, etc.
If paper had a similar system for example for World or Entity, plugin developers could attach cache data to the player object. Whenever the player object gets cleared (or disposed) the cached data would be invalidated. Meaning, instead of requiring a Map<UUID, MyParticlePlayer> in any not so nice "ParticlePlayerHandler" class, I could attach my MyParticlePlayer to the player object directly, using a Key<MyParticlePlayer> as key. Why would I need a ParticlePlayer instance if the player is offline, so the lifespan of the player object always frames the lifespan of the ParticlePlayer. (Additionally by combining both mechanics, I could link the ParticlePlayer as Disposable to the World object it is playing in, so if the world gets deleted OR the player goes offline, the disposer takes care of the ParticlePlayer).

Jetbrains pushes this to the point where a value can be cached and listens to certain changes in its holder, like cached values on an AST node become invalidated once the AST changes or, transferred to minecraft, cached values in the entities data become invalid if its location changes for example.

I know especially the second suggestion implies big changes but I thought about it so much that I felt like I had to at least suggest it once. Plugin reloading after all became discouraged because you could run into artifacts of the previous plugin instance, like not freed singletons and stuff. Disposables are the way jetbrains handles the (de)activation of plugins at any time and only under some conditions enforces a restart. Plugins that failed to load don't needlessly occupy memory and so on.

Describe alternatives you've considered.

None, its additional features

Other

No response

[lynxplay]

Thank you for the suggestion!

I am unsure if implementing either of these suggestions is something I personally think benefits the API enough to justify the tremendous amount of diff we'd have to maintain.

Disposable
The existing code does not care for the concept of object lifetimes on a fundamental level.
A world is managed completely different from a plugin or entity.
There is already events for this if plugins care for it. Implementing a observer like approach that automagically disposes stuff just combats the existing event API, which isn't something I'd be happy to see.
The bit more verbosity imo is not an issue.
I can see the use case for a ton of plugin initialised state, but automagically unloading them feels a bit meh from the API.
In the end, something like this could very well just be an opinionated third party library that makes use of the respective events when things are "disposed".

PluginDataHolder
I don't see a single benefit of this over a plugin maintained Map<UUID, Data>.
You'll need some form of manager for this anyway or you have to initial all of your state for e.g. players on join.
Otherwise you need some instance to load on first request, at which point, that thing can also just maintain the map itself?

Events already exist (as described above) to catch "disposals".
Forcing this onto the API just means we take away control from plugin developers in regards to their Map implementation, loading mechanism and data disposal.
It does not offer speed benefits either, now we maintain some arbitrary key instance in a hashmap on each thing.

End
Overall I can certainly see that this kind of framework might be a great developer experience, however I do not believe that it is objectively great enough for us to invest the initial implementation effort and, more importantly, the upkeep of such API.
I think most if not all of this could be done via a third party library.
Disposer.get().register(this, myPlugin); specifically can 1 to 1 be implemented by third party already listening to plugin disable event.
The Map abstraction that is plugin data holders in the end is the same with one more uuid map lookup.

I'll leave this open for other team members to comment on, thank you again for the suggestion it was certainly an interesting read.

[CubBossa]

I get your point, there is actually no reason this should be part of paper explicitly. Especially Disposable could be a pretty nice library on its own. Here is btw the jetbrains explanation of how Disposable works. They use them in combination with their event system and listeners can be linked to a disposable to restrict their lifetime to that object too (for example a world specific listener to a world if World were disposable). But I also see that minecraft listeners are usually more broad and filter the player within the listener callback rather than having one listener per player.

[CubBossa]

https://github.com/CubBossa/Disposables
Made a simple implementation of the disposables idea here since I had need for it in my projects