Snippet

Guaranteed One-Time Initialization via sync.Once

The sync.Once type guarantees that a function is executed exactly once across all goroutines. This is commonly used for thread-safe lazy initialization, such as setting up global configurations, connection pools, or singletons, without needing explicit locks or manual double-checked locking.

snippet.go

package main
 
import (
	"fmt"
	"sync"
)
 
type Config struct {
	Value string
}
 
var (
	instance *Config
	once     sync.Once
)
 
func GetConfig() *Config {
	once.Do(func() {
		instance = &Config{Value: "Initialized"}
	})
	return instance
}
 
func main() {
	c1 := GetConfig()
	c2 := GetConfig()
	fmt.Println(c1 == c2) // true
}

Breakdown

once sync.Once

Declares a sync.Once variable to coordinate execution state.

once.Do(func() { ... })

Executes the passed function exactly once. Subsequent calls to Do block until the first execution completes, and then return immediately without running the function again.

return instance

Returns the initialized global pointer, ensuring all callers receive the same reference.

Previous snippet Next snippet

More Intermediate Go exercises →

Guaranteed One-Time Initialization via sync.Once

Related