code: public void retryOperation(Operation op) {
      if (retryQueueSize >= 0 && retryOps.size() >= retryQueueSize) {
        if (!op.isCancelled()) {
          op.cancel();
        }
      }
      retryOps.add(op);
    }
docs: Add a operation to the retry queue.
  
  If the retry queue size is bounded and the size of the queue is reaching
  that boundary, the operation is cancelled rather than added to the
  retry queue.
  
  @param op the operation to retry.