How to stop CoreML from running when it's no longer needed in the app?

Question

My app runs Vision on a CoreML model. The camera frames the machine learning model runs on are from an ARKit sceneView (basically, the camera). I have a method that's called loopCoreMLUpdate() that continuously runs CoreML so that we keep running the model on new camera frames. The code looks like this:

import UIKit
import SceneKit
import ARKit

class MyViewController: UIViewController {
    var visionRequests = [VNRequest]()
    let dispatchQueueML = DispatchQueue(label: "com.hw.dispatchqueueml") // A Serial Queue

    override func viewDidLoad() {
        super.viewDidLoad()

        // Setup ARKit sceneview
        // ...

        // Begin Loop to Update CoreML
        loopCoreMLUpdate()
    }

    // This is the problematic part. 
    // In fact - once it's run there's no way to stop it, is there?
    func loopCoreMLUpdate() {
        // Continuously run CoreML whenever it's ready. (Preventing 'hiccups' in Frame Rate)

        dispatchQueueML.async {
            // 1. Run Update.
            self.updateCoreML()

            // 2. Loop this function.
            self.loopCoreMLUpdate()
        }   
    }

    func updateCoreML() {
        ///////////////////////////
        // Get Camera Image as RGB
        let pixbuff : CVPixelBuffer? = (sceneView.session.currentFrame?.capturedImage)
        if pixbuff == nil { return }
        let ciImage = CIImage(cvPixelBuffer: pixbuff!)
        // Note: Not entirely sure if the ciImage is being interpreted as RGB, but for now it works with the Inception model.
        // Note2: Also uncertain if the pixelBuffer should be rotated before handing off to Vision (VNImageRequestHandler) - regardless, for now, it still works well with the Inception model.

        ///////////////////////////
        // Prepare CoreML/Vision Request
        let imageRequestHandler = VNImageRequestHandler(ciImage: ciImage, options: [:])
        // let imageRequestHandler = VNImageRequestHandler(cgImage: cgImage!, orientation: myOrientation, options: [:]) // Alternatively; we can convert the above to an RGB CGImage and use that. Also UIInterfaceOrientation can inform orientation values.

        ///////////////////////////
        // Run Image Request
        do {
            try imageRequestHandler.perform(self.visionRequests)
        } catch {
            print(error)
        }

    }

}

As you can see the loop effect is created by a DispatchQueue with the label com.hw.dispatchqueueml that keeps calling loopCoreMLUpdate(). Is there any way to stop the queue once CoreML is not needed anymore? Full code is here.

Answer 1

I suggest instead o running coreML model here in viewDidLoad, you can use ARSessionDelegate function for the same. func session(_ session: ARSession, didUpdate frame: ARFrame) method to get the frame, you can set the flag, here to enable when you want the the model to work and when you dont. Like this below:

func session(_ session: ARSession, didUpdate frame: ARFrame) { // This is where we will analyse our frame

      // We return early if currentBuffer is not nil or the tracking state of camera is not normal

    // TODO: - Core ML Functionality Commented
      guard isMLFlow else { //
             return
      }
      currentBuffer = frame.capturedImage
      guard let buffer = currentBuffer, let image = UIImage(pixelBuffer: buffer) else { return }
     <Code here to load model>
      CoreMLManager.manager.updateClassifications(for: image)
}