thought for www.v2ex.com/t/755876

main.go

package main

import (
	"log"
	"math/rand"
	"sync"
	"time"
)

func main() {
	c := make(chan int)
	rc := make(chan int)

	go func() {
		for i := 0; i < 10; i++ {
			time.Sleep(time.Duration(rand.Intn(10))*time.Millisecond)
			c <- i
		}
	}()

	wg := sync.WaitGroup{}
	wg.Add(5)

	for i := 0; i < 4; i++ {
		go func() {
		out:
			for {
				select {
				case t := <-c:
					time.Sleep(time.Duration(rand.Intn(1000))*time.Millisecond)
					rc <- (t + 10)
				case <-time.After(time.Second):
					break out
				}
			}
			wg.Done()
		}()
	}

	go func() {
	out:
		for {
			select {
			case t := <-rc:
				time.Sleep(time.Duration(rand.Intn(100))*time.Millisecond)
				log.Println(t)
			case <-time.After(time.Second):
				break out
			}
		}
		wg.Done()
	}()
	wg.Wait()
}