115 lines
2.6 KiB
Go
115 lines
2.6 KiB
Go
|
package maxcache
|
||
|
|
|
||
|
|
import (
|
||
|
|
"context"
|
||
|
|
"sync"
|
||
|
|
"time"
|
||
|
|
|
||
|
|
"github.com/cespare/xxhash/v2"
|
||
|
|
"github.com/goware/singleflight"
|
||
|
|
lru "github.com/hashicorp/golang-lru/v2"
|
||
|
|
)
|
||
|
|
|
||
|
|
func NewCache[K comparable, V any](size int, freshFor, ttl time.Duration) *Cache[K, V] {
|
||
|
|
values, _ := lru.New[K, value[V]](size)
|
||
|
|
return &Cache[K, V]{
|
||
|
|
values: values,
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
type Cache[K comparable, V any] struct {
|
||
|
|
values *lru.Cache[K, value[V]]
|
||
|
|
|
||
|
|
mu sync.RWMutex
|
||
|
|
callGroup singleflight.Group[K, V]
|
||
|
|
}
|
||
|
|
|
||
|
|
func (c *Cache[K, V]) Get(ctx context.Context, key K, fn singleflight.DoFunc[V]) (V, error) {
|
||
|
|
return c.get(ctx, key, false, fn)
|
||
|
|
}
|
||
|
|
|
||
|
|
func (c *Cache[K, V]) GetFresh(ctx context.Context, key K, fn singleflight.DoFunc[V]) (V, error) {
|
||
|
|
return c.get(ctx, key, true, fn)
|
||
|
|
}
|
||
|
|
|
||
|
|
func (c *Cache[K, V]) Set(ctx context.Context, key K, fn singleflight.DoFunc[V]) (V, bool, error) {
|
||
|
|
v, err, shared := c.callGroup.Do(key, c.set(key, fn))
|
||
|
|
return v, shared, err
|
||
|
|
}
|
||
|
|
|
||
|
|
func (c *Cache[K, V]) get(ctx context.Context, key K, freshOnly bool, fn singleflight.DoFunc[V]) (V, error) {
|
||
|
|
c.mu.RLock()
|
||
|
|
val, ok := c.values.Get(key)
|
||
|
|
c.mu.RUnlock()
|
||
|
|
|
||
|
|
// value exists and is fresh - just return
|
||
|
|
if ok && val.IsFresh() {
|
||
|
|
return val.Value(), nil
|
||
|
|
}
|
||
|
|
|
||
|
|
// value exists and is stale, and we're OK with serving it stale while updating in the background
|
||
|
|
// note: stale means its still okay, but not fresh. but if its expired, then it means its useless.
|
||
|
|
if ok && !freshOnly && !val.IsExpired() {
|
||
|
|
// TODO: technically could be a stampede of goroutines here if the value is expired
|
||
|
|
// and we're OK with serving it stale
|
||
|
|
go c.Set(ctx, key, fn)
|
||
|
|
return val.Value(), nil
|
||
|
|
}
|
||
|
|
|
||
|
|
// value doesn't exist or is expired, or is stale and we need it fresh (freshOnly:true) - sync update
|
||
|
|
v, _, err := c.Set(ctx, key, fn)
|
||
|
|
return v, err
|
||
|
|
}
|
||
|
|
|
||
|
|
func (c *Cache[K, V]) set(key K, fn singleflight.DoFunc[V]) singleflight.DoFunc[V] {
|
||
|
|
return singleflight.DoFunc[V](func() (V, error) {
|
||
|
|
val, err := fn()
|
||
|
|
if err != nil {
|
||
|
|
return val, err
|
||
|
|
}
|
||
|
|
|
||
|
|
c.mu.Lock()
|
||
|
|
c.values.Add(key, value[V]{
|
||
|
|
v: val,
|
||
|
|
})
|
||
|
|
c.mu.Unlock()
|
||
|
|
|
||
|
|
return val, nil
|
||
|
|
})
|
||
|
|
}
|
||
|
|
|
||
|
|
type value[V any] struct {
|
||
|
|
v V
|
||
|
|
|
||
|
|
bestBefore time.Time // cache entry freshness cutoff
|
||
|
|
expiry time.Time // cache entry time to live cutoff
|
||
|
|
}
|
||
|
|
|
||
|
|
func (v *value[V]) IsFresh() bool {
|
||
|
|
return v.bestBefore.After(time.Now())
|
||
|
|
}
|
||
|
|
|
||
|
|
func (v *value[V]) IsExpired() bool {
|
||
|
|
return v.expiry.Before(time.Now())
|
||
|
|
}
|
||
|
|
|
||
|
|
func (v *value[V]) Value() V {
|
||
|
|
return v.v
|
||
|
|
}
|
||
|
|
|
||
|
|
func BytesToHash(b ...[]byte) uint64 {
|
||
|
|
d := xxhash.New()
|
||
|
|
for _, v := range b {
|
||
|
|
d.Write(v)
|
||
|
|
}
|
||
|
|
return d.Sum64()
|
||
|
|
}
|
||
|
|
|
||
|
|
func StringToHash(s ...string) uint64 {
|
||
|
|
d := xxhash.New()
|
||
|
|
for _, v := range s {
|
||
|
|
d.WriteString(v)
|
||
|
|
}
|
||
|
|
return d.Sum64()
|
||
|
|
}
|