Example of channels, etc.

mobile-example.go

package main

import (
	"context"
	"fmt"
	"math/rand"
	"time"
)

// Pretend we are finding tokens from the db and stream them over a channel.
func getTargets(ctx context.Context, out chan<- string) {
	for i := 0; ; i++ {
		select {
		case <-ctx.Done():
			fmt.Println("Cancelling getTargets...")
			return
		case out <- fmt.Sprintf("target %d", i):
			time.Sleep(time.Second * 1)
		}
	}
}

// Pretend to process them by sending to e.g. Firebase
func processTargets(ctx context.Context, targets <-chan string, errorChan chan<- error) {
	for target := range targets {
		select {
		case <-ctx.Done():
			fmt.Println("Cancelling processTargets...")
			return
		default:
			fmt.Printf("processing %s\n", target)
			if rand.Float64() < 0.2 {
				fmt.Printf("simulating error for %s\n", target)
				errorChan <- fmt.Errorf("error for %s", target)
			}
		}
	}
}

// Pretend to process errors
func handleErrors(ctx context.Context, errs <-chan error) {
	for err := range errs {
		select {
		case <-ctx.Done():
			fmt.Println("Cancelling handleErrors...")
			return
		default:
			fmt.Printf("handling %v\n", err)
		}
	}

	return
}

func main() {
	ctx, cancel := context.WithCancel(context.Background())

	errChan := make(chan error, 1)
	targetChan := make(chan string, 1)

	go getTargets(ctx, targetChan)
	go processTargets(ctx, targetChan, errChan)
	go handleErrors(ctx, errChan)

	time.Sleep(time.Second * 10)
	cancel()
	time.Sleep(time.Second * 2)
}