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| package main
import (
"errors"
"fmt"
"sync"
"github.com/golang/groupcache/singleflight"
)
func main() {
var wg sync.WaitGroup
for i := 0; i < 500; i++ {
wg.Add(1)
go func(n int) {
var mchId = "12345"
var mch, err = mchCache.GetMch(mchId)
fmt.Println(n, mch, err)
wg.Done()
}(i)
}
wg.Wait()
}
type MchCache struct {
Mchs map[string]MchInfo
sync.RWMutex
g singleflight.Group
}
type MchInfo struct {
ID string
Name string
}
var mchCache MchCache
var errMchNotFound = errors.New("mch not found in cache")
func (c *MchCache) GetMch(id string) (mch MchInfo, err error) {
mch, err = c.getMch(id)
if err == nil {
return
}
m, err := c.g.Do(id, func() (interface{}, error) {
return c.getMchFromDB(id)
})
if err != nil {
return
}
mch = m.(MchInfo)
return
}
func (c *MchCache) getMch(id string) (mch MchInfo, err error) {
c.RLock()
defer c.RUnlock()
if c.Mchs == nil {
c.Mchs = make(map[string]MchInfo)
}
if mch, ok := c.Mchs[id]; ok {
return mch, nil
}
return mch, errMchNotFound
}
func (c *MchCache) SetMch(mch MchInfo) {
c.Lock()
defer c.Unlock()
if c.Mchs == nil {
c.Mchs = make(map[string]MchInfo)
}
c.Mchs[mch.ID] = mch
return
}
func (c *MchCache) getMchFromDB(id string) (mch MchInfo, err error) {
mch = MchInfo{
ID: id,
Name: "星巴克",
}
c.SetMch(mch)
return
}
|