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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package atomic_test
import (
func loadConfig() map[string]string {
return make(map[string]string)
func requests() chan int {
return make(chan int)
// The following example shows how to use Value for periodic program config updates
// and propagation of the changes to worker goroutines.
func ExampleValue_config() {
var config atomic.Value // holds current server configuration
// Create initial config value and store into config.
go func() {
// Reload config every 10 seconds
// and update config value with the new version.
for {
time.Sleep(10 * time.Second)
// Create worker goroutines that handle incoming requests
// using the latest config value.
for i := 0; i < 10; i++ {
go func() {
for r := range requests() {
c := config.Load()
// Handle request r using config c.
_, _ = r, c
// The following example shows how to maintain a scalable frequently read,
// but infrequently updated data structure using copy-on-write idiom.
func ExampleValue_readMostly() {
type Map map[string]string
var m atomic.Value
var mu sync.Mutex // used only by writers
// read function can be used to read the data without further synchronization
read := func(key string) (val string) {
m1 := m.Load().(Map)
return m1[key]
// insert function can be used to update the data without further synchronization
insert := func(key, val string) {
mu.Lock() // synchronize with other potential writers
defer mu.Unlock()
m1 := m.Load().(Map) // load current value of the data structure
m2 := make(Map) // create a new value
for k, v := range m1 {
m2[k] = v // copy all data from the current object to the new one
m2[key] = val // do the update that we need
m.Store(m2) // atomically replace the current object with the new one
// At this point all new readers start working with the new version.
// The old version will be garbage collected once the existing readers
// (if any) are done with it.
_, _ = read, insert