code: func (f *DeltaFIFO) HasSynced() bool {
  	f.lock.Lock()
  	defer f.lock.Unlock()
  	return f.populated && f.initialPopulationCount == 0
  }
docs: // Return true if an Add/Update/Delete/AddIfNotPresent are called first,
  // or an Update called first but the first batch of items inserted by Replace() has been popped