code: func (pool *TxPool) stats() (int, int) {
  	pending := 0
  	for _, list := range pool.pending {
  		pending += list.Len()
  	}
  	queued := 0
  	for _, list := range pool.queue {
  		queued += list.Len()
  	}
  	return pending, queued
  }
docs: // stats retrieves the current pool stats, namely the number of pending and the
  // number of queued (non-executable) transactions.