Push ComponentState into the scheduler instead of boxed runners

[WorldSEnder]

Suggestion

The scheduler for component lifecycles currently pushes boxed runners into the queue, incurring an allocation. A stable memory allocation is already available, in the form of a Rc<ComponentState> for each component. This could be used to store the pending lifecycle events similar to the MsgQueue that was introduced as part of #2421. An implementation should not re-introduce the generics that were removed as part of that PR.

See also: #2330 (comment)

Questionnaire

• I'm interested in fixing this myself but don't know where to start
• I would like to fix and I have a solution
• I don't have time to fix this right now, but maybe later

[przembot]

Hi, interested in picking this up, which solution should be preferred?

1. Replace Box<dyn Runnable> in scheduler with enum Task which would contain task kind, Rc<ComponentState> and relevant data and matched runners for each Task variant.
2. Replace scheduler queues with a main one with Rc<ComponentState>, where the ComponentState would contain a queue of tasks to be done on the component. This would though remove the scheduling depending on the task kind which is now present

[WorldSEnder]

Hi, interested in picking this up, which solution should be preferred?

1. Replace `Box<dyn Runnable>` in scheduler with enum `Task` which would contain task kind, `Rc<ComponentState>` and relevant data and matched runners for each `Task` variant.

2. Replace scheduler queues with a main one with `Rc<ComponentState>`, where the ComponentState would contain a queue of tasks to be done on the component. This would though remove the scheduling depending on the task kind which is now present

The different task queues should be retained and run in the same order. Note that each task queue, except for create (generic over COMP) and main (for user tasks) contains only a single type of task, hence Boxing those is unnecessary.

Since I opened the issue, the implementation has changed a bit. Most impls then were generic in the type of BaseComponent like CreateRunner still is. Now, runners such as UpdateRunner are monomorphized, so the easiest solution is to e.g. replace destroy: Vec<Box<dyn Runnable>> with destroy: Vec<DestroyRunner>. Bonus points if you find a way to get rid of the generic argument in CreateRunner without adding more allocations, I think this should be possible, but might be a bit more fiddly.