Go channel experiment: see if what would result in select under various channel conditions.

main.go

package main

/*
See if what would result in select under various channel conditions.

Outputs:
- On mode = 1 (worker-1): "Got error: error at 2017-10-15 19:33:00.687713221 ...  (ok: true)"
- On mode = 2 (worker-2): "Got error: <nil> (ok: true)"
- On mode = 3 (worker-2): "Got error: <nil> (ok: false)"
- On mode = -9 (timeout): "Have context done."
*/

import (
	"context"
	"fmt"
	"os"
	"strconv"
	"time"
)

func channelWorker1(d time.Duration, ch chan<- error) {
	time.Sleep(d)
	err := fmt.Errorf("error at %v", time.Now())
	ch <- err
}

func channelWorker2(d time.Duration, ch chan<- error) {
	time.Sleep(d)
	ch <- nil
}

func channelWorker3(d time.Duration, ch chan<- error) {
	time.Sleep(d)
	close(ch)
}

func getWaitSeconds(mode int) (worker1, worker2, worker3, timeout time.Duration) {
	if 1 == mode {
		return 1, 3, 5, 7
	} else if 2 == mode {
		return 3, 1, 5, 7
	} else if 3 == mode {
		return 3, 5, 1, 7
	}
	return 9, 9, 9, 1
}

func main() {
	mode, _ := strconv.Atoi(os.Args[1])
	worker1Idle, worker2Idle, worker3Idle, timeoutIdle := getWaitSeconds(mode)
	errChannel := make(chan error)
	go channelWorker1(time.Second*worker1Idle, errChannel)
	go channelWorker2(time.Second*worker2Idle, errChannel)
	go channelWorker3(time.Second*worker3Idle, errChannel)
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*timeoutIdle)
	defer cancel()
	select {
	case err, ok := <-errChannel:
		fmt.Printf("[mode: %v] Got error: %v (ok: %v)\n", mode, err, ok)
	case <-ctx.Done():
		fmt.Printf("[mode: %v] Have context done.\n", mode)
	}
}