Memory leak in CardboardActivity

Question

While profiling my Google Cardboard application, I found out a very large memory leak (15Mb!) each time I left the activity with the 3D graphics.

After a long and grievous investigation, I found out that the source of the problem was a Context leak that happened each time I closed my CardboardActivity subclass.

The solution can be found in the accepted answer*

* wow... this is awkward... Note for any kind (and experienced) reviewer: I am writing a question to whom I know the answer already: am I supposed to do something for style, like add some fake suspense ("will our heroes prevail?! Find out in the accepted answer!"), like in a old Batman TV series or something?

Answer 1

After dicing and slicing my CardboardActivity subclass, until nothing else but the base class remained, I had to conclude that the base class itself was leaking the context.

I searched the web and found this post explaining how the activity in question leaked the context by failing to un-register a listener with a private instance of a class.

Upon trying to invoke said method manually (using reflection), I found out that in the current version of the Cardboard SDK (0.5.4 at the time of writing), the field is not present anymore.

Long story short: all sensors are now handled by an undocumented (yet public) SensorConnection class instantiated in CardboardActivity as a sensorConnection field, which is still plagued by the bug detailed in my first link.

This led me to this solution:

• get the sensorConnection field in the CardboardActivity by reflection
• use it to get the magneticSensor field, again by reflection
• invoke the setOnCardboardTheaterListener with null argument, to clear the binding holding the reference to the Context in the Activity onDestroy method.

this boils down to the following code:

private void workAroundLeak() {
    try {
        // Get the sensor Connection
        Class<?> c1 = Class.forName("com.google.vrtoolkit.cardboard.CardboardActivity");
        Field sensorsField = c1.getDeclaredField("sensorConnection");
        sensorsField.setAccessible(true);
        SensorConnection sc = (SensorConnection) sensorsField.get(this);
        if(sc == null) return;

        // Get the magnetSensor
        Class<?> c2 = Class.forName("com.google.vrtoolkit.cardboard.sensors.SensorConnection");
        Field magnetField = c2.getDeclaredField("magnetSensor");
        magnetField.setAccessible(true);
        MagnetSensor ms = (MagnetSensor) magnetField.get(sc);
        if(ms == null) return;

        ms.setOnCardboardTriggerListener(null);
    } catch(Exception e) {}
}

@Override
protected void onDestroy() {
    workAroundLeak();
    super.onDestroy();
}

which solved the problem entirely.

A word to the wise: since this solution relies on reflection, it might break (without consequences other than doing nothing, likely) as soon as Google will update the SDK (possibly fixing the issue in a clean way).

Hope this helps someone