code: func (f *asyncFlusher) start(numParallel int) {
  	f.chunks = make(chan chunk)
  	for i := 0; i < numParallel; i++ {
  		f.wg.Add(1)
  		go func() {
  			defer f.wg.Done()
  			f.uploaderLoop()
  		}()
  	}
  }
docs: // start launches internal goroutines that upload data.