golang实现单例模式

import (
    "sync"
)

type singleton struct {
}

var _instance *singleton
var _once sync.Once

func GetInstance() *singleton {
	_once.Do(func() {
		instance = &singleton{}
	})
	return instance
}

package sync

import (
	"sync/atomic"
)


type Once struct {
	done uint32
	m    Mutex
}

func (o *Once) Do(f func()) {

	if atomic.LoadUint32(&o.done) == 0 {
		// Outlined slow-path to allow inlining of the fast-path.
		o.doSlow(f)
	}
}

func (o *Once) doSlow(f func()) {
	o.m.Lock()
	defer o.m.Unlock()
	if o.done == 0 {
        //取done的索引地址作为key保存
		defer atomic.StoreUint32(&o.done, 1)
		f()
	}
}