registro gcm no background

RegisterInBackground.java

private void registerInBackground(){
    new AsyncTask<Void,Void,String>(){
        @Override
        protected String doInBackground(Void... arg0){
            String msg = "";
            try{
                if(gcm == null){
                    gcm = GoogleCloudMessaging.getInstance(context);
                }
                regid = gcm.register(SENDER_ID);
                msg = "Registred:" + regid;
                if(sendRegistrationIdToBackend(regid)){
                    storeRegistrationId(context,regid);
                }
            } catch (IOException ex){
                ex.printStackTrace();
            }
            return msg;
        }
    }