sync.Once 多次调用一次执行的方法

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demo

package mainimport (        "fmt"        "sync")func main() {        var once sync.Once        onceFunc := func() {                fmt.Println("this func do once")        }        done := make(chan bool)        for i := 0; i < 10; i++ {                go func() {                        once.Do(onceFunc)                        done <- true                }()        }        for i := 0; i < 10; i++ {                <-done        }}

output

liqiongtao:test liqiongtao$ go run main.go this func do once

Once源码

// Copyright 2009 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 syncimport (        "sync/atomic")// Once is an object that will perform exactly one action.type Once struct {        m    Mutex        done uint32}// Do calls the function f if and only if Do is being called for the// first time for this instance of Once. In other words, given//         var once Once// if once.Do(f) is called multiple times, only the first call will invoke f,// even if f has a different value in each invocation. A new instance of// Once is required for each function to execute.//// Do is intended for initialization that must be run exactly once. Since f// is niladic, it may be necessary to use a function literal to capture the// arguments to a function to be invoked by Do://         config.once.Do(func() { config.init(filename) })//// Because no call to Do returns until the one call to f returns, if f causes// Do to be called, it will deadlock.//// If f panics, Do considers it to have returned; future calls of Do return// without calling f.//func (o *Once) Do(f func()) {        if atomic.LoadUint32(&o.done) == 1 {                return        }        // Slow-path.        o.m.Lock()        defer o.m.Unlock()        if o.done == 0 {                defer atomic.StoreUint32(&o.done, 1)                f()        }}

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