tour: [missing sync.WaitGroup calls (or similar) can lead to wrong output]

[ziqueiros]

Context: https://go.dev/tour/concurrency/1

The problems is that this sample is missing Wait() / Done() calls to guarantee proper execution. If you don't want to introduce this topic at this point my suggestion is to create a slide after this introducing the topic and maybe even asking to verify if the output was correct. Have a nice day!

It must be something like:

package main

import (
	"fmt"
	"sync" 
	"time"
)

func say(s string, wg *sync.WaitGroup) {
	defer wg.Done() // Decrement the counter when the goroutine finishes
	for i := 0; i < 5; i++ {
		time.Sleep(100 * time.Millisecond)
		fmt.Println(s)
	}
}

func main() {
	var wg sync.WaitGroup // Declare a WaitGroup

	wg.Add(1) // Increment the counter for the "world" goroutine
	go say("world", &wg) // Pass the address of the WaitGroup

	say("hello", nil) // No need for WaitGroup for the "hello" call as it's on the main goroutine
	                  // or you could also use it if you want to be consistent in the function signature

	wg.Wait() // Block until the counter becomes zero (i.e., "world" goroutine finishes)
	fmt.Println("Both goroutines have completed.")
}