[AR开发]报错：Scene is modified withi

[SceneKit] Error: Scene <SCNScene: 0x284ebcfa0> is modified within a rendering callback of another scene (<SCNScene: 0x28099c820>). This is not allowed and may lead to crash

此错误是因为我在renderer的代理方法中，初始化SCNNode：

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
        DispatchQueue.main.async { [weak self] in
            let node = SCNScene(named: "art.scnassets/demo.scn")!.rootNode.childNode(withName: "demo", recursively: false)
            
        }
    }

应该在viewDidLoad中或者其他地方初始化。