Awaiters, fixed

using Godot;
using System.Collections.Generic;
using System.Threading.Tasks;

public partial class Awaiters : Node
{
	static Awaiters _instance;
	public static Awaiters Instance => _instance;

	static SceneTree Tree => Instance.GetTree();
	public static SignalAwaiter WaitNextFrame() => Tree.ToSignal(Tree, "process_frame");
	public static SignalAwaiter WaitSeconds(float s) => Tree.ToSignal(Tree.CreateTimer(s), "timeout");

	List<System.Action> _oneshots = new List<System.Action>();
	List<System.Action> _processingOneshots = new List<System.Action>();

	public Awaiters() : base()
	{
		if (_instance != null)
		{
			GD.PrintErr($"Multiple instances of {typeof(Awaiters).Name} Singletons created!");
			return;
		}

		_instance = this;
	}

	public override void _Notification(long what)
	{
		base._Notification(what);
		if (what == NotificationWmCloseRequest)
		{
			_instance = null;
		}
	}

	void _ProcessOneshots()
	{
		var temp = _processingOneshots;
		_processingOneshots = _oneshots;
		_oneshots = temp;
		_oneshots.Clear();

		foreach (var action in _processingOneshots) action?.Invoke();
	}

	public static void AddOneshot(System.Action oneshot)
	{
		if(Instance == null) return;
		Instance._oneshots.Add(oneshot);
		Instance.SetProcess(true);
	}

	public static void CancelOneshot(System.Action oneshot)
	{
		if(Instance == null) return;
		Instance._oneshots.Remove(oneshot);
	}

	public override void _Process(double delta)
	{
		base._Process(delta);
		_ProcessOneshots();
		SetProcess(_oneshots.Count > 0);
	}
}