code: func (ct *costTracker) subscribeTotalRecharge(ch chan uint64) uint64 {
  	ct.gfLock.Lock()
  	defer ct.gfLock.Unlock()
  
  	ct.totalRechargeCh = ch
  	return uint64(ct.gf * ct.utilTarget)
  }
docs: // subscribeTotalRecharge returns all future updates to the total recharge value
  // through a channel and also returns the current value