@Override
    public void dispose() {
        disposables.dispose();
        obtainMessage(0, new CancelHolder(CancelHolder.CANCEL_CALLBACK)).sendToTarget();
    }
Cancel the current handler. This can be called from any thread. The disposables
added with {@link #add(Disposable)} will be disposed immediately, while the
{@link #handleDispose()} callback will be called synchronously by the handler.
main/src/main/java/cgeo/geocaching/utils/DisposableHandler.java