Fan in

main.go

package main

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

func main() {

	r := fanIn(work(1), work(2))

	for v := range r {
		fmt.Println(v)
	}
}

func work(sleepDur int) <-chan int {
	c := make(chan int)

	go func() {
		for i := 0; i < 3; i++ {
			c <- i
			time.Sleep(time.Duration(sleepDur) * time.Second)
		}
		fmt.Println("done working")
		close(c)
	}()

	return c
}

func fanIn(a, b <-chan int) <-chan int {

	out := make(chan int)

	var wg sync.WaitGroup
	
	wg.Add(2)

	go func() {
		for {
			o, ok := <-a

			if !ok {
				wg.Done()
				break
			}

			out <- o
		}
	}()

	go func() {
		for {
			o, ok := <-b

			if !ok {
				wg.Done()
				break
			}

			out <- o
		}
	}()
	
	
	go func() {
		wg.Wait()
		fmt.Println("Closing out")
		close(out)
	}()

	return out

}