Harden AndroidRendererFrontend::reduceMemoryUse

[tobrun]

Only allow invoking OnLowMemory with an active renderer.
Closes #14603

[LukasPaczos]

I'm not sure this check is enough. Check out this diff, which is still going to crash when we launch the map:

diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapView.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapView.java
index b04b1f827..fde151882 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapView.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapView.java
@@ -295,7 +295,7 @@ public class MapView extends FrameLayout implements NativeMapView.ViewCallback {
     } else {
       GLSurfaceView glSurfaceView = new GLSurfaceView(getContext());
       glSurfaceView.setZOrderMediaOverlay(mapboxMapOptions.getRenderSurfaceOnTop());
-      mapRenderer = new GLSurfaceViewMapRenderer(getContext(), glSurfaceView, localFontFamily) {
+      mapRenderer = new GLSurfaceViewMapRenderer(this, getContext(), glSurfaceView, localFontFamily) {
         @Override
         public void onSurfaceCreated(GL10 gl, EGLConfig config) {
           MapView.this.onSurfaceCreated();
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/renderer/glsurfaceview/GLSurfaceViewMapRenderer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/renderer/glsurfaceview/GLSurfaceViewMapRenderer.java
index aa36dace7..85b01589e 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/renderer/glsurfaceview/GLSurfaceViewMapRenderer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/renderer/glsurfaceview/GLSurfaceViewMapRenderer.java
@@ -4,6 +4,8 @@ import android.content.Context;
 import android.opengl.GLSurfaceView;
 import android.support.annotation.NonNull;
 import android.view.SurfaceHolder;
+
+import com.mapbox.mapboxsdk.maps.MapView;
 import com.mapbox.mapboxsdk.maps.renderer.MapRenderer;
 import com.mapbox.mapboxsdk.maps.renderer.egl.EGLConfigChooser;
 
@@ -23,7 +25,7 @@ public class GLSurfaceViewMapRenderer extends MapRenderer implements GLSurfaceVi
   @NonNull
   private final GLSurfaceView glSurfaceView;
 
-  public GLSurfaceViewMapRenderer(Context context,
+  public GLSurfaceViewMapRenderer(final MapView mapView, Context context,
                                   GLSurfaceView glSurfaceView,
                                   String localIdeographFontFamily) {
     super(context, localIdeographFontFamily);
@@ -39,6 +41,7 @@ public class GLSurfaceViewMapRenderer extends MapRenderer implements GLSurfaceVi
       public void surfaceCreated(SurfaceHolder holder) {
         super.surfaceCreated(holder);
         hasSurface = true;
+        mapView.onLowMemory();
       }
 
       @Override

The pointer is initialized on GL thread in MapRenderer#onSurfaceCreated and from quick testing, it seems like SurfaceHolderCallbackAdapter#surfaceCreated that sets the flag is called consistently sooner than MapRenderer#onSurfaceCreated.

[LukasPaczos]

Can that also mean that we are misusing the MapRenderer#hasSurface flag? It's not thread safe and we are accessing it from multiple threads in GLSurfaceViewMapRenderer#requestRender.

[tobrun]

1c8f2c9

re. threadsafity, replaced hasSurface with AtomicBoolean to ensure thread safety. lmk if you feel another construct would be more appropriate here.

re. not sure this check is enough, yes you are correct we need to make sure that the renderer is actually created and that only happens after setting the hasSurface call and on the main thread. Adding an additional check to MapView#onLowMemory fixes that, MapboxMap will always be created after the renderer.