| // Copyright 2012 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 sync_test |
| |
| import ( |
| "fmt" |
| "os" |
| "sync" |
| ) |
| |
| type httpPkg struct{} |
| |
| func (httpPkg) Get(url string) {} |
| |
| var http httpPkg |
| |
| // This example fetches several URLs concurrently, |
| // using a WaitGroup to block until all the fetches are complete. |
| func ExampleWaitGroup() { |
| var wg sync.WaitGroup |
| var urls = []string{ |
| "http://www.golang.org/", |
| "http://www.google.com/", |
| "http://www.example.com/", |
| } |
| for _, url := range urls { |
| // Increment the WaitGroup counter. |
| wg.Add(1) |
| // Launch a goroutine to fetch the URL. |
| go func(url string) { |
| // Decrement the counter when the goroutine completes. |
| defer wg.Done() |
| // Fetch the URL. |
| http.Get(url) |
| }(url) |
| } |
| // Wait for all HTTP fetches to complete. |
| wg.Wait() |
| } |
| |
| func ExampleOnce() { |
| var once sync.Once |
| onceBody := func() { |
| fmt.Println("Only once") |
| } |
| 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 |
| } |
| |
| // This example uses OnceValue to perform an "expensive" computation just once, |
| // even when used concurrently. |
| func ExampleOnceValue() { |
| once := sync.OnceValue(func() int { |
| sum := 0 |
| for i := 0; i < 1000; i++ { |
| sum += i |
| } |
| fmt.Println("Computed once:", sum) |
| return sum |
| }) |
| done := make(chan bool) |
| for i := 0; i < 10; i++ { |
| go func() { |
| const want = 499500 |
| got := once() |
| if got != want { |
| fmt.Println("want", want, "got", got) |
| } |
| done <- true |
| }() |
| } |
| for i := 0; i < 10; i++ { |
| <-done |
| } |
| // Output: |
| // Computed once: 499500 |
| } |
| |
| // This example uses OnceValues to read a file just once. |
| func ExampleOnceValues() { |
| once := sync.OnceValues(func() ([]byte, error) { |
| fmt.Println("Reading file once") |
| return os.ReadFile("example_test.go") |
| }) |
| done := make(chan bool) |
| for i := 0; i < 10; i++ { |
| go func() { |
| data, err := once() |
| if err != nil { |
| fmt.Println("error:", err) |
| } |
| _ = data // Ignore the data for this example |
| done <- true |
| }() |
| } |
| for i := 0; i < 10; i++ { |
| <-done |
| } |
| // Output: |
| // Reading file once |
| } |