Simple goroutines and channels implementation for concurrent processing.

online_checker.go

/*
 * Package statuschecker checks the status of a given url and prints the online status
 * to the console.
 */

package main

import (
	"fmt"
	"net/http"
	"time"
)

func main() {
	links := []string{
		"https://google.com",
		"https://facebook.com",
		"https://stackoverflow.com",
		"https://golang.org",
		"https://amazon.com",
	}

	// Channels are used to communicate in between different running go routines
	c := make(chan string)

	for _, link := range links {
		go checkLink(link, c)
	}

	// using a range with a channel allows us to retrieve a value sent
	// to the channel and assign it to a variable.
	for l := range c {
		// l variable is defined in the outer scope of the function literal and maintained
		// by another goroutine. In order to share this variable with other goroutines, we need
		// to pass it as an argument to a function literal so they receive a copy of it.
		go func(link string) {
			time.Sleep(3 * time.Second)
			checkLink(link, c)
		}(l)
	}
}

// checkLink function makes an HTTP request to the link parameter in order to check
// if the url is online and sends the link back to the main go routine.
func checkLink(link string, c chan string) {
	_, err := http.Get(link)

	if err != nil {
		fmt.Println(link, "might be down!")
		// sending a message back to the main go routine
		c <- link
		return
	}

	fmt.Println(link, "is up!")
	// sending a message back to the main go routine
	c <- link
}