From 2295554db6503cc47eb0cfb69c59cc5b740f5f0e Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Thu, 1 Mar 2012 22:16:20 +0400
Subject: [PATCH] sync: add Once example

R=golang-dev, rsc, bradfitz
CC=golang-dev
https://golang.org/cl/5715046
---
 src/pkg/sync/example_test.go | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/pkg/sync/example_test.go b/src/pkg/sync/example_test.go
index 1424b1e79e6..15649240035 100644
--- a/src/pkg/sync/example_test.go
+++ b/src/pkg/sync/example_test.go
@@ -5,6 +5,7 @@
 package sync_test
 
 import (
+	"fmt"
 	"net/http"
 	"sync"
 )
@@ -32,3 +33,22 @@ func ExampleWaitGroup() {
 	// Wait for all HTTP fetches to complete.
 	wg.Wait()
 }
+
+func ExampleOnce() {
+	var once sync.Once
+	onceBody := func() {
+		fmt.Printf("Only once\n")
+	}
+	done := make(chan bool)
+	for i := 0; i < 10; i++ {
+		go func() {
+			once.Do(onceBody)
+			done <- true
+		}()
+	}
+	for i := 0; i < 10; i++ {
+		<-done
+	}
+	// Output:
+	// Only once
+}