code: private synchronized void retryInterest(RetryContext context) throws IOException {
      LOGGER.info("Retrying interest: " + context.interest.toUri());
      context.face.expressInterest(context.interest, context, context);
      totalRetries++;
    }
docs: Synchronized helper method to prevent multiple threads from mashing
  totalRetries
  
  @param context the current request context
  @throws IOException when the client cannot perform the necessary network IO