mirror of https://go.googlesource.com/go
114 lines
2.2 KiB
Go
114 lines
2.2 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package sync_test
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import (
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"fmt"
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"os"
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"sync"
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)
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type httpPkg struct{}
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func (httpPkg) Get(url string) {}
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var http httpPkg
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// This example fetches several URLs concurrently,
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// using a WaitGroup to block until all the fetches are complete.
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func ExampleWaitGroup() {
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var wg sync.WaitGroup
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var urls = []string{
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"http://www.golang.org/",
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"http://www.google.com/",
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"http://www.example.com/",
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}
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for _, url := range urls {
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// Increment the WaitGroup counter.
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wg.Add(1)
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// Launch a goroutine to fetch the URL.
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go func(url string) {
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// Decrement the counter when the goroutine completes.
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defer wg.Done()
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// Fetch the URL.
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http.Get(url)
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}(url)
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}
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// Wait for all HTTP fetches to complete.
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wg.Wait()
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}
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func ExampleOnce() {
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var once sync.Once
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onceBody := func() {
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fmt.Println("Only once")
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}
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done := make(chan bool)
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for i := 0; i < 10; i++ {
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go func() {
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once.Do(onceBody)
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done <- true
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}()
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}
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for i := 0; i < 10; i++ {
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<-done
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}
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// Output:
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// Only once
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}
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// This example uses OnceValue to perform an "expensive" computation just once,
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// even when used concurrently.
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func ExampleOnceValue() {
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once := sync.OnceValue(func() int {
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sum := 0
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for i := 0; i < 1000; i++ {
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sum += i
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}
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fmt.Println("Computed once:", sum)
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return sum
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})
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done := make(chan bool)
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for i := 0; i < 10; i++ {
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go func() {
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const want = 499500
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got := once()
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if got != want {
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fmt.Println("want", want, "got", got)
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}
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done <- true
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}()
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}
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for i := 0; i < 10; i++ {
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<-done
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}
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// Output:
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// Computed once: 499500
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}
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// This example uses OnceValues to read a file just once.
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func ExampleOnceValues() {
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once := sync.OnceValues(func() ([]byte, error) {
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fmt.Println("Reading file once")
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return os.ReadFile("example_test.go")
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})
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done := make(chan bool)
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for i := 0; i < 10; i++ {
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go func() {
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data, err := once()
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if err != nil {
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fmt.Println("error:", err)
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}
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_ = data // Ignore the data for this example
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done <- true
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}()
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}
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for i := 0; i < 10; i++ {
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<-done
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}
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// Output:
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// Reading file once
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}
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