select.go

package main

import (
	"fmt"
	"math/rand"
	"reflect"
)

func worker(n int, ch chan int) {
	count := rand.Intn(5) + 3
	x := n
	for i := 0; i < count; i++ {
		ch <- x
		x *= n
	}
	close(ch)
}

const N = 5

func main() {
	chs := make([]chan int, N)
	for i := 0; i < N; i++ {
		chs[i] = make(chan int)
		go worker(2 + i, chs[i])
	}

	selectCases := make([]reflect.SelectCase, N)
	for i := 0; i < N; i++ {
		selectCases[i].Dir = reflect.SelectRecv
		selectCases[i].Chan = reflect.ValueOf(chs[i])
	}

	numDone := 0
	for numDone < N {
		chosen, recv, recvOk := reflect.Select(selectCases)
		if recvOk {
			fmt.Printf("From %d: %d\n", 2 + chosen, recv.Int())
		} else {
			numDone++
		}
	}
}