Automatic pruning of LRU cache

.github/workflows/on-pull-request.yaml

@@ -14,6 +14,7 @@ jobs:
         go-version:
           - 1.22.x
           - 1.23.x
+          - 1.24.x
         os: [ ubuntu-latest ]
     runs-on: ${{ matrix.os }}
     steps:

groupcache.go

@@ -106,8 +106,31 @@ func GetGroups() []*Group {
 // completes.
 //
 // The group name must be unique for each getter.
-func NewGroup(name string, cacheBytes int64, getter Getter) *Group {
-	return newGroup(name, cacheBytes, getter, nil)
+func NewGroup(name string, cacheBytes int64, getter Getter, opts ...Option) *Group {
+	group := newGroup(name, cacheBytes, getter, nil)
+	for _, opt := range opts {
+		opt.apply(group)
+	}
+	return group
+}
+
+// Option for NewGroup().
+type Option interface {
+	apply(*Group)
+}
+
+type withPruneIntervalOption struct {
+	pruneInterval int
+}
+
+func (o *withPruneIntervalOption) apply(group *Group) {
+	group.mainCache.pruneInterval = o.pruneInterval
+	group.hotCache.pruneInterval = o.pruneInterval
+}
+
+// Pass prune interval option for NewGroup().
+func WithPruneInterval(pruneInterval int) Option {
+	return &withPruneIntervalOption{pruneInterval: pruneInterval}
 }
 
 // DeregisterGroup removes group from group pool
@@ -608,11 +631,12 @@ var NowFunc lru.NowFunc = time.Now
 // makes values always be ByteView, and counts the size of all keys and
 // values.
 type cache struct {
-	mu         sync.RWMutex
-	nbytes     int64 // of all keys and values
-	lru        *lru.Cache
-	nhit, nget int64
-	nevict     int64 // number of evictions
+	mu            sync.RWMutex
+	nbytes        int64 // of all keys and values
+	lru           *lru.Cache
+	nhit, nget    int64
+	nevict        int64 // number of evictions
+	pruneInterval int
 }
 
 func (c *cache) stats() CacheStats {
@@ -638,6 +662,7 @@ func (c *cache) add(key string, value ByteView) {
 				c.nbytes -= int64(len(key.(string))) + int64(val.Len())
 				c.nevict++
 			},
+			PruneInterval: c.pruneInterval,
 		}
 	}
 	c.lru.Add(key, value, value.Expire())

lru/lru.go

@@ -39,8 +39,13 @@ type Cache struct {
 	// Defaults to time.Now()
 	Now NowFunc
 
-	ll    *list.List
-	cache map[interface{}]*list.Element
+	// PruneInterval sets number of cache removals before internal map is pruned.
+	// If set to zero, no pruning is performed.
+	PruneInterval int
+
+	ll            *list.List
+	cache         map[interface{}]*list.Element
+	removeCounter int
 }
 
 // A Key may be any value that is comparable. See http://golang.org/ref/spec#Comparison_operators
@@ -69,6 +74,9 @@ func (c *Cache) Add(key Key, value interface{}, expire time.Time) {
 	if c.cache == nil {
 		c.cache = make(map[interface{}]*list.Element)
 		c.ll = list.New()
+	} else if c.PruneInterval > 0 && c.removeCounter >= c.PruneInterval {
+		c.removeCounter = 0
+		c.Prune()
 	}
 	if ee, ok := c.cache[key]; ok {
 		eee := ee.Value.(*entry)
@@ -131,6 +139,7 @@ func (c *Cache) removeElement(e *list.Element) {
 	c.ll.Remove(e)
 	kv := e.Value.(*entry)
 	delete(c.cache, kv.key)
+	c.removeCounter++
 	if c.OnEvicted != nil {
 		c.OnEvicted(kv.key, kv.value)
 	}
@@ -155,3 +164,16 @@ func (c *Cache) Clear() {
 	c.ll = nil
 	c.cache = nil
 }
+
+// Prune cache state to flush map storage from previously deleted keys.
+func (c *Cache) Prune() {
+	if c.cache == nil {
+		return
+	}
+	newCache := make(map[any]*list.Element)
+	for k, v := range c.cache {
+		newCache[k] = v
+		delete(c.cache, k)
+	}
+	c.cache = newCache
+}