[Android] Memory leak on JmeSurfaceView

[pavly-gerges]

According to this thread, there is a memory leak, the test was conducted on JmeSurfaceView.

A proposed blind solution was to add JmeSystemDelegate.setView(null) within the JmeSurfaceView#destroy(), which surprisingly was already on AndroidHarness, I think this is a real memory leak that is specific to JmeSurfaceView.

[pavly-gerges]

Confirmed Memory Leak of the JmeSurfaceView#context, in addition to its dependencies that were prevented from being GC'ed, at the hosting Activity:

Cause: Deep investigations have shown that the JmeSurfaceView#destroy(), a concrete implementation of the JME SystemListener#destroy(), is not dispatched properly.... The dispatch was placed in the Activity#onDestroy() which is as the Android documentation says, it's a KILLABLE function (i.e., Android System controls can play an interpart in whether the onDestroy() is dispatched or not or being interrupted).

Fix: A proposed fix is to refactor this part:

 public void onStateChanged(@NonNull LifecycleOwner source, @NonNull Lifecycle.Event event) {
        switch (event) {
            case ON_DESTROY:
                /*destroy only if the policy flag is enabled*/
                if (destructionPolicy == DestructionPolicy.DESTROY_WHEN_FINISH) {
                    legacyApplication.stop(!isGLThreadPaused());
                }
                break;
            case ON_PAUSE:
                loseFocus();
                break;
            case ON_RESUME:
                gainFocus();
                break;
            case ON_STOP:
                jmeSurfaceViewLogger.log(Level.INFO, "Context stops, but game is still running");
                break;
        }
    }

To this part:

public void onStateChanged(@NonNull LifecycleOwner source, @NonNull Lifecycle.Event event) {
        switch (event) {
            case ON_DESTROY:
                jmeSurfaceViewLogger.log(Level.INFO, "Destruction dispatched.");
                break;
            case ON_PAUSE:
                // activity is still on the foreground stack but not
                // on the topmost level
                // activity is no longer visible and is out of foreground
                if (((Activity) getContext()).isFinishing() 
                                     && (destructionPolicy == DestructionPolicy.DESTROY_WHEN_FINISH)) {
                    legacyApplication.stop(!isGLThreadPaused());
                } else {
                    loseFocus();
                }
                break;
            case ON_RESUME:
                // activity is back to the topmost of the
                // foreground stack
                gainFocus();
                break;
            case ON_STOP:
                jmeSurfaceViewLogger.log(Level.INFO, "Context stops, but game is still running");
                break;
        }
    }

In addition to other optimizations on the JmeSurfaceView#destroy().

Also, the Activity#onStop() is also a KILLABLE, so it shouldn't be used to control the JME context resources; because it will lead to a system-dependent unstable behavior (i.e., unpredictable behavior).