fix: resolve race condition when starting AVCaptureSession (#93)

Author: phantumcode

Sources/FaceLiveness/AV/LivenessCaptureSession.swift

@@ -11,6 +11,7 @@ import AVFoundation
 class LivenessCaptureSession {
     let captureDevice: LivenessCaptureDevice
     private let captureQueue = DispatchQueue(label: "com.amazonaws.faceliveness.cameracapturequeue")
+    private let configurationQueue = DispatchQueue(label: "com.amazonaws.faceliveness.sessionconfiguration", qos: .userInitiated)
     let outputDelegate: AVCaptureVideoDataOutputSampleBufferDelegate
     var captureSession: AVCaptureSession?
 
@@ -43,6 +44,7 @@ class LivenessCaptureSession {
         else { throw LivenessCaptureSessionError.cameraUnavailable }
 
         let cameraInput = try AVCaptureDeviceInput(device: camera)
+        let videoOutput = AVCaptureVideoDataOutput()
 
         teardownExistingSession(input: cameraInput)
         captureSession = AVCaptureSession()
@@ -53,13 +55,10 @@ class LivenessCaptureSession {
 
         try setupInput(cameraInput, for: captureSession)
         captureSession.sessionPreset = captureDevice.preset
-
-        let videoOutput = AVCaptureVideoDataOutput()
         try setupOutput(videoOutput, for: captureSession)
-
         try captureDevice.configure()
 
-        DispatchQueue.global().async {
+        configurationQueue.async {
             captureSession.startRunning()
         }
 

Sources/FaceLiveness/Views/Liveness/FaceLivenessDetectionView.swift

@@ -172,6 +172,9 @@ public struct FaceLivenessDetectorView: View {
                     UIScreen.main.brightness = 1.0
                 }
             }
+            .onDisappear() {
+                viewModel.stopRecording()
+            }
             .onReceive(viewModel.$livenessState) { output in
                 switch output.state {
                 case .completed:

Sources/FaceLiveness/Views/Liveness/LivenessViewController.swift

@@ -37,6 +37,12 @@ final class _LivenessViewController: UIViewController {
             }
         }
     }
+    
+    deinit {
+        self.previewLayer.removeFromSuperlayer()
+        (self.previewLayer as? AVCaptureVideoPreviewLayer)?.session = nil
+        self.previewLayer = nil
+    }
 
     override func viewDidLoad() {
         super.viewDidLoad()
@@ -110,6 +116,7 @@ extension _LivenessViewController: FaceLivenessViewControllerPresenter {
             imageView.frame = self.previewLayer.frame
             self.view.addSubview(imageView)
             self.previewLayer.removeFromSuperlayer()
+            (self.previewLayer as? AVCaptureVideoPreviewLayer)?.session = nil
             self.viewModel.stopRecording()
         }
     }