Untested method of registering and unregstering broadcast channels

broadcast.go

func manager() {
  chans := map[chan data]bool
  active := sync.WaitGroup{}
  for {
    select {
    case c := <-register:
      chans[c] = true
    case c := <-unregister:
      active.Wait()
      delete(chans, c)
      close(c)
    case d := <-broadcast:
      current := make([]chan data, 0, len(chans))
      for c := range chans {
        current = append(current, c)
      }
      active.Add(1)
      go func(d data) {
        defer active.Done()
        for _, c := range current {
          c <- d
        }
      }(d)
    }
  }
}