@Override
    public final boolean isDisposed() {
        return unsubscribed.get();
    }
Verify that the calling thread is the Android main thread.
<p>
Calls to this method are usually preconditions for subscription behavior which instances of
this class later undo. See the class documentation for an example.

@throws IllegalStateException when called from any other thread.
android/android_framework/base/src/main/java/rx2/android/MainThreadDisposable.java