error selection

selectErrors.go

package main

import (
	"fmt"
	"time"
)

type e struct{}

func chanErr(produceErr bool, d time.Duration, noErrChan chan e) chan e {
	c := make(chan e)
	go func() {
		time.Sleep(d)
		if !produceErr {
			noErrChan <- e{}
		} else {
			close(c)
		}
	}()
	return c
}

func println(msg string) {
	fmt.Printf("[%s] %s\n",
		time.Now().Format("2006-01-02 15:04:05.999999999"),
		msg)
}

func allPassed(checkNum int) (finishChan, noErrChan chan e) {
	noErrChan = make(chan e, checkNum)
	finishChan = make(chan e)
	go func() {
		for {
			select {
			case <-noErrChan:
				checkNum--
				if checkNum == 0 {
					close(finishChan)
					return
				}
			case <-finishChan:
				return
			}
		}
	}()
	return
}

func main() {
	println("start")

	var produceErr bool
	// produceErr = true

	timeOut := time.NewTimer(time.Second * 2)
	defer timeOut.Stop()

	finishChan, noErrChan := allPassed(4)

	errA := chanErr(produceErr, time.Second, noErrChan)
	errB := chanErr(produceErr, time.Second/2, noErrChan)
	errC := chanErr(produceErr, time.Second/3, noErrChan)
	errD := chanErr(produceErr, time.Second/4, noErrChan)

	var passed bool
	select {
	case <-errA:
		println("got error A")
	case <-errB:
		println("got error B")
	case <-errC:
		println("got error C")
	case <-errD:
		println("got error D")
	case <-finishChan:
		passed = true
		println("all passed")
	case <-timeOut.C:
		println("time out!")
	}

	if passed {
		close(finishChan)
	}
	return
}

https://blog.golang.org/pipelines

https://golang.org/ref/spec#Receive_operator