Issue with chapter09/concurrency/once/main.go

[rhysmeister]

Hello,

I had an issue with the execution of this example. With the default code I got the following output (nearly always, once or two I got two "Hello, friend!" messages...

https://github.com/PacktPublishing/Test-Driven-Development-in-Go/blob/main/chapter09/concurrency/once/main.go

~/git/Test-Driven-Development-in-Go/chapter09/concurrency/once$ go run main.go
Hello, friend!
Channel closed.
Goodbye, friend!

Fixed it with wait groups but perhaps there's a simpler way...

package main

import (
	"fmt"
	"sync"
)

var wg sync.WaitGroup

func safelyClose(once *sync.Once, ch chan struct{}) {
	defer wg.Done()
	fmt.Println("Hello, friend!")
	once.Do(func() {
		fmt.Println("Channel closed.")
		close(ch)
	})
}

func main() {
	var once sync.Once

	ch := make(chan struct{})
	for i := 0; i < 3; i++ {
		wg.Add(1)
		go safelyClose(&once, ch)
	}
	<-ch
	wg.Wait()
	fmt.Println("Goodbye, friend!")
}

~/git/Test-Driven-Development-in-Go/chapter09/concurrency/once$ go run main.go
Hello, friend!
Channel closed.
Hello, friend!
Hello, friend!
Goodbye, friend!

[rhysmeister]

Hello,

Also had similar issues with other bit of this chapter, for example concurrency/data-races and concurrency/buffered-channels. I'm using go version 1.21.3