code: public RetryBuilder doOnRetry(Action4<Integer, Throwable, Long, TimeUnit> doOnRetryAction) {
      this.doOnRetryAction = doOnRetryAction;
      return this;
    }
docs: Execute some code each time a retry is scheduled (at the moment the retriable exception
  is caught, but before the retry delay is applied). Only quick executing code should be
  performed, do not block in this action.
  <p>
  The action receives the retry attempt number (1-n), the exception that caused the retry,
  the delay duration and timeunit for the scheduled retry.
  
  @param doOnRetryAction the side-effect action to perform whenever a retry is scheduled.
  @see OnRetryAction if you want a shorter signature.