call arcore.destroy off of main thread Fixes SceneView#407 (SceneView#408)

* call arcore.destroy off of main thread

* rename method as per PR comment

---------

Co-authored-by: Sameer Jiwani <>

Author: sameerjj

arsceneview/src/main/java/io/github/sceneview/ar/ARSceneView.kt

@@ -7,6 +7,7 @@ import androidx.activity.ComponentActivity
 import androidx.lifecycle.DefaultLifecycleObserver
 import androidx.lifecycle.Lifecycle
 import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.coroutineScope
 import com.google.android.filament.Engine
 import com.google.android.filament.IndirectLight
 import com.google.android.filament.MaterialInstance
@@ -44,6 +45,9 @@ import io.github.sceneview.model.Model
 import io.github.sceneview.model.ModelInstance
 import io.github.sceneview.node.LightNode
 import io.github.sceneview.node.Node
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
 
 /**
  * A SurfaceView that integrates with ARCore and renders a scene
@@ -561,7 +565,7 @@ open class ARSceneView @JvmOverloads constructor(
 
     override fun destroy() {
         if (!isDestroyed) {
-            arCore.destroy()
+            destroyARCore()
 
             defaultCameraNode?.destroy()
             defaultCameraStream?.destroy()
@@ -573,6 +577,14 @@ open class ARSceneView @JvmOverloads constructor(
         super.destroy()
     }
 
+    fun destroyARCore() {
+        val scope = lifecycle?.coroutineScope ?: CoroutineScope(Dispatchers.IO)
+        scope.launch(Dispatchers.IO) {
+            // destroy should be called off the main thread since it hangs for many seconds
+            arCore.destroy()
+        }
+    }
+
     class DefaultARCameraNode(engine: Engine) : ARCameraNode(engine) {
         init {
             // Set the exposure on the camera, this exposure follows the sunny f/16 rule
@@ -596,7 +608,7 @@ open class ARSceneView @JvmOverloads constructor(
         }
 
         override fun onDestroy(owner: LifecycleOwner) {
-            arCore.destroy()
+            destroyARCore()
         }
     }