adv3.go

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {

	wg := sync.WaitGroup{}
	wg.Add(1)
	input := run(&wg)

	for i := 0; i < 10; i++ {
		input <- i + 1
		time.Sleep(time.Millisecond * 20)
	}
	close(input)
	fmt.Println("close")
	wg.Wait()
}

func run(wg *sync.WaitGroup) (input chan int) {
	input = make(chan int)
	work := make(chan int)

	var items []int

	go func() {
		defer wg.Done()
		for w := range work {
			fmt.Println("work", w)
			time.Sleep(time.Second * 2)
		}
	}()

	go func() {
	mainLoop:
		for {
			var item int
			var sendWork chan int
		inner:
			for len(items) > 0 {
				sendWork = work
				item = items[0]
				select {
				case sendWork <- item:
					fmt.Println("send to worker", item)
					items = items[1:]
				default:
					break inner
				}
			}

			select {
			case i, ok := <-input:
				if ok {
					fmt.Println("receive", i)
					items = append(items, i)
				} else if len(items) == 0 {
					fmt.Println("Close queue")
					close(work)
					break mainLoop
				}
			case sendWork <- item:
				fmt.Println("send to worker", item)
				items = items[1:]
			}
		}
	}()

	return
}