for-select loop for a feed reader as presented in "Advanced Go Concurrency Patterns" (Sameer Ajmani, Google I/O 2013)

for-select.go

func (s *sub) loop() {
    var pending []Item // appended by fetch; consumed by send
    var next time.Time // initially January 1, year 0
    var err error // set when Fetch fails

    for {
  	var first Item
		var updates chan Item
		if len(pending) > 0 {
			first = pending[0]
			updates = s.updates // enable send case
		}
		var fetchDelay time.Duration // initally 0 (no delay)
		if now := time.Now(); next.After(now) {
			fetchDelay = next.Sub(now)
		}
		startFetch := time.After(fetchDelay)
		
		select {
		case errc := <-s.closing:
			errc <- err
			close(s.updates)
			return
		case <-startFetch:
			var fetched []Item
			fetched, next, err = s.fetcher.Fetch()
			if err != nil {
				next = time.Now().Add(10 * time.Second)
				break
			}
			pending = append(pending, fetched...)
		case updates <- first:
			pending = pending[1:]
		}
	}
}