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