[android] Cherry picks to agua

platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/snapshot/MapSnapshotterMarkerActivity.java

@@ -25,6 +25,8 @@
  */
 public class MapSnapshotterMarkerActivity extends AppCompatActivity implements MapSnapshotter.SnapshotReadyCallback {
 
+  private MapSnapshotter mapSnapshotter;
+
   @Override
   protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
@@ -40,7 +42,7 @@ public void onGlobalLayout() {
 
           Timber.i("Starting snapshot");
 
-          MapSnapshotter mapSnapshotter = new MapSnapshotter(
+          mapSnapshotter = new MapSnapshotter(
             getApplicationContext(),
             new MapSnapshotter
               .Options(Math.min(container.getMeasuredWidth(), 1024), Math.min(container.getMeasuredHeight(), 1024))

platform/android/src/map_renderer.cpp

@@ -41,15 +41,19 @@ ActorRef<Renderer> MapRenderer::actor() const {
 }
 
 void MapRenderer::schedule(std::weak_ptr<Mailbox> scheduled) {
-    // Create a runnable and schedule it on the gl thread
+    // Create a runnable
     android::UniqueEnv _env = android::AttachEnv();
     auto runnable = std::make_unique<MapRendererRunnable>(*_env, std::move(scheduled));
 
+    // Obtain ownership of the peer (gets transferred to the MapRenderer on the JVM for later GC)
+    auto peer = runnable->peer();
+
+    // Queue the event on the Java Peer
     static auto queueEvent = javaClass.GetMethod<void(
             jni::Object<MapRendererRunnable>)>(*_env, "queueEvent");
-    javaPeer->Call(*_env, queueEvent, runnable->getPeer());
+    javaPeer->Call(*_env, queueEvent, *peer);
 
-    // Release the object as it will be destroyed on GC of the Java Peer
+    // Release the c++ peer as it will be destroyed on GC of the Java Peer
     runnable.release();
 }
 

platform/android/src/map_renderer_runnable.cpp

@@ -8,11 +8,13 @@ namespace android {
 MapRendererRunnable::MapRendererRunnable(jni::JNIEnv& env, std::weak_ptr<Mailbox> mailbox_)
     : mailbox(std::move(mailbox_)) {
 
-    // Create the Java peer
+    // Create the Java peer and hold on to a global reference
+    // Not using a weak reference here as this might oerflow
+    // the weak reference table on some devices
     jni::UniqueLocalFrame frame = jni::PushLocalFrame(env, 5);
     static auto constructor = javaClass.GetConstructor<jlong>(env);
     auto instance = javaClass.New(env, constructor, reinterpret_cast<jlong>(this));
-    javaPeer = SeizeGenericWeakRef(env, jni::Object<MapRendererRunnable>(jni::NewWeakGlobalRef(env, instance.Get()).release()));
+    javaPeer = instance.NewGlobalRef(env);
 }
 
 MapRendererRunnable::~MapRendererRunnable() = default;
@@ -21,8 +23,8 @@ void MapRendererRunnable::run(jni::JNIEnv&) {
     Mailbox::maybeReceive(mailbox);
 }
 
-jni::Object<MapRendererRunnable> MapRendererRunnable::getPeer() {
-    return *javaPeer;
+jni::UniqueObject<MapRendererRunnable> MapRendererRunnable::peer() {
+    return std::move(javaPeer);
 }
 
 // Static methods //

platform/android/src/map_renderer_runnable.hpp

@@ -8,8 +8,6 @@
 
 #include <jni/jni.hpp>
 
-#include "jni/generic_global_ref_deleter.hpp"
-
 namespace mbgl {
 namespace android {
 
@@ -39,10 +37,11 @@ class MapRendererRunnable {
 
     void run(jni::JNIEnv&);
 
-    jni::Object<MapRendererRunnable> getPeer();
+    // Transfers ownership of the Peer object to the caller
+    jni::UniqueObject<MapRendererRunnable> peer();
 
 private:
-    GenericUniqueWeakObject<MapRendererRunnable> javaPeer;
+    jni::UniqueObject<MapRendererRunnable> javaPeer;
     std::weak_ptr<Mailbox> mailbox;
 };