memcache

a mem cache base on other populator cache, add following feacture

1. add lazy load(using expired data, and load it asynchronous)
2. add singleflight for data loading

setup backend db

type Item struct {
	I int
}

var m map[string]*Item

func init() {
	m = map[string]*Item{}
	for i := 0; i < 1000; i++ {
		m[fmt.Sprintf("item-%d", i)] = &Item{i}
	}
}

func load(key string) (value interface{}, ttl time.Duration, err error) {
	v, ok := m[key]
	if !ok {
		return nil, 0, errors.New("not found")
	}
	return v, time.Millisecond * 10, nil
}

golang std map version

cache := memcache.NewWithStdMapCache(memcache.LoaderFunc(load),time.Millisecond*20)
cache.SetWithTTL("item-2", &Item{100}, time.Millisecond*10)
v, ok := cache.Get("item-2")

ristretto version

ristretto, err := ristretto.NewCache(&ristretto.Config{
		NumCounters: 1e7,     // number of keys to track frequency of (10M).
		MaxCost:     1 << 30, // maximum cost of cache (1GB).
		BufferItems: 64,      // number of keys per Get buffer.
	})
	if err != nil {
		panic(err)
	}
cache := memcache.NewWithRistretto(memcache.LoaderFunc(load), time.Millisecond*20, ristretto)
time.Sleep(time.Millisecond * 2) // only for ristretto
cache.SetWithTTL("item-2", &Item{100}, time.Millisecond*10)
v, ok := cache.Get("item-2")