Prevent the main() function from terminating before goroutines finish in Golang

Question

Have loook at this contrived example:

package main

import \"fmt\"

func printElo() {
    fmt.Printf(\"Elo\\n\")
}

func printHello() {
    fmt.Printf(\"Hel         


        

Answer 1

Simplest, cleanest and "scalable" way to do it is to use a sync.WaitGroup:

var wg = &sync.WaitGroup{}

func printElo() {
    defer wg.Done()
    fmt.Printf("Elo\n")
}

func printHello() {
    defer wg.Done()
    fmt.Printf("Hello\n")
}

func main() {
    fmt.Printf("This will print.")
    i := 0
    for i < 10 {
        wg.Add(1)
        go printElo()
        wg.Add(1)
        go printHello()
        i++
    }
    wg.Wait()
}

Output (try it on the Go Playground):

This will print.Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo

Simple "rules" to follow when doing it with sync.WaitGroup:

• call WaitGroup.Add() in the "original" goroutine (that starts a new) before the go statement
• recommended to call WaitGroup.Done() deferred, so it gets called even if the goroutine panics
• if you want to pass WaitGroup to other functions (and not use a global variable), you must pass a pointer to it, else the WaitGroup (which is a struct) would be copied, and the Done() method called on the copy wouldn't be observed on the original