Sync.Once

syncOnce.go

package main

import (
	"log"
	"sync"
)

type MyStruct struct {
	field int
}

var onceCached *MyStruct

func initMyStruct() MyStruct {
	return MyStruct{field: 1}
}

var once sync.Once

func getIntOnce(ident int) *MyStruct {
	log.Println("No lock", ident)

	once.Do(func() {
		log.Println("Initializing GetInt")
		x := initMyStruct()
		onceCached = &x
	})

	log.Println("No lock return", ident)

	return onceCached
}

func main() {
	var wg sync.WaitGroup
	for x := range []int{0, 1, 2, 3, 4, 5} {
		wg.Add(1)
		go func(ident int) {
			defer wg.Done()
			log.Println(getIntOnce(ident))
		}(x)
	}

	wg.Wait()
}