Entity deletion (with finalizer support)

[SOF3]

Maintain a deletion_flag: Vec<bool> and finalizer_count: Vec<AtomicUsize> for each archetype.

Entity creation

• Count the components that are finalizers, stored to finalizer_count
• Initialize deletion_flag as false.

Entity deletion flagging

• Offline mode: accepts an entity: impl entity::Ref, get the raw ID and drop(entity).
• Online mode: accepts an entity: impl entity::Ref, get the raw ID, push the raw ID to a sharded queue, process in batch after join.
• During offline/join: If finalizer count is zero, proceed to "Entity deletion". Otherwise, set deletion_flag to true to wait for trigger from finalizers.

Component update

If a component is removed and the deletion flag for its entity is true, the entity is queued for finalizer test after join.

Entity deletion

• Check the refcount of the entity, ensure that the internal refcount is the only reference.
• Loop through all storages, drop the component from the storage if exists.
• Deallocate the entity ID.