feat: implement lfu based cache strategy

go.mod

@@ -30,6 +30,7 @@ require (
 	github.com/lestrrat-go/iter v1.0.2 // indirect
 	github.com/lestrrat-go/option v1.0.0 // indirect
 	github.com/miekg/dns v1.1.53 // indirect
+	github.com/mitchellh/hashstructure/v2 v2.0.2 // indirect
 	golang.org/x/sync v0.1.0 // indirect
 	google.golang.org/genproto v0.0.0-20210226172003-ab064af71705 // indirect
 	google.golang.org/grpc v1.35.0 // indirect

go.sum

@@ -258,6 +258,8 @@ github.com/miekg/dns v0.0.0-20161006100029-fc4e1e2843d8/go.mod h1:W1PPwlIAgtquWB
 github.com/miekg/dns v1.1.41/go.mod h1:p6aan82bvRIyn+zDIv9xYNUpwa73JcSh9BKwknJysuI=
 github.com/miekg/dns v1.1.53 h1:ZBkuHr5dxHtB1caEOlZTLPo7D3L3TWckgUUs/RHfDxw=
 github.com/miekg/dns v1.1.53/go.mod h1:uInx36IzPl7FYnDcMeVWxj9byh7DutNykX4G9Sj60FY=
+github.com/mitchellh/hashstructure/v2 v2.0.2 h1:vGKWl0YJqUNxE8d+h8f6NJLcCJrgbhC4NcD46KavDd4=
+github.com/mitchellh/hashstructure/v2 v2.0.2/go.mod h1:MG3aRVU/N29oo/V/IhBX8GR/zz4kQkprJgF2EVszyDE=
 github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
 github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyuac5Z2hdY=
 github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=

pkg/storage/driver/cache/lfu/cache.go

@@ -0,0 +1,313 @@
+package lfu
+
+import (
+	"sync"
+	"sync/atomic"
+
+	"github.com/pkg/errors"
+)
+
+var (
+	ErrNotFound           = errors.New("not found")
+	ErrSizeExceedCapacity = errors.New("size exceed capacity")
+)
+
+type Cache[K comparable, V any] struct {
+	index *Map[K, *CacheItem[K, V]]
+	freqs *List[*FrequencyItem[K, V]]
+
+	size atomic.Int32
+
+	capacity     int
+	store        Store[K, V]
+	getValueSize GetValueSizeFunc[V]
+	sync         *Synchronizer[K]
+
+	evictMutex sync.Mutex
+
+	log LogFunc
+}
+
+type CacheItem[K any, V any] struct {
+	key             K
+	size            int
+	frequencyParent *Element[*FrequencyItem[K, V]]
+}
+
+func NewCacheItem[K any, V any](key K, size int) *CacheItem[K, V] {
+	item := &CacheItem[K, V]{
+		key:  key,
+		size: size,
+	}
+	return item
+}
+
+type FrequencyItem[K any, V any] struct {
+	entries *Map[*CacheItem[K, V], struct{}]
+	freq    int
+}
+
+func NewFrequencyItem[K any, V any]() *FrequencyItem[K, V] {
+	frequencyItem := &FrequencyItem[K, V]{}
+	frequencyItem.entries = NewMap[*CacheItem[K, V], struct{}]()
+	return frequencyItem
+}
+
+func (c *Cache[K, V]) Set(key K, value V) error {
+	newItemSize, err := c.getValueSize(value)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	c.log("setting '%v' (size: %d)", key, newItemSize)
+
+	if newItemSize > int(c.capacity) {
+		return errors.WithStack(ErrSizeExceedCapacity)
+	}
+
+	var sizeDelta int
+
+	err = c.sync.WriteTx(key, func() error {
+		if err := c.store.Set(key, value); err != nil {
+			return errors.WithStack(err)
+		}
+
+		item, ok := c.index.Get(key)
+		if ok {
+			oldItemSize := item.size
+			sizeDelta = -int(oldItemSize) + newItemSize
+
+		} else {
+			item = NewCacheItem[K, V](key, newItemSize)
+			c.index.Set(key, item)
+			sizeDelta = newItemSize
+		}
+
+		c.size.Add(int32(sizeDelta))
+		c.increment(item)
+
+		return nil
+	})
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	// Eviction, if needed
+	if err := c.Evict(); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func (c *Cache[K, V]) Get(key K) (V, error) {
+	var value V
+	err := c.sync.WriteTx(key, func() error {
+		c.log("getting '%v'", key)
+
+		e, ok := c.index.Get(key)
+		if !ok {
+			return errors.WithStack(ErrNotFound)
+		}
+
+		v, err := c.store.Get(key)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+
+		c.increment(e)
+
+		value = v
+		return nil
+	})
+	if err != nil {
+		return *new(V), errors.WithStack(err)
+	}
+
+	return value, nil
+}
+
+func (c *Cache[K, V]) Delete(key K) error {
+	err := c.sync.WriteTx(key, func() error {
+		c.log("deleting '%v'", key)
+
+		item, exists := c.index.Get(key)
+		if !exists {
+			return errors.WithStack(ErrNotFound)
+		}
+
+		if err := c.store.Delete(key); err != nil {
+			return errors.WithStack(err)
+		}
+
+		c.size.Add(-int32(item.size))
+
+		c.remove(item.frequencyParent, item)
+		c.index.Delete(key)
+
+		return nil
+	})
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func (c *Cache[K, V]) Len() int {
+	return c.index.Len()
+}
+
+func (c *Cache[K, V]) Size() int {
+	return int(c.size.Load())
+}
+
+func (c *Cache[K, V]) Capacity() int {
+	return c.capacity
+}
+
+func (c *Cache[K, V]) increment(item *CacheItem[K, V]) {
+	currentFrequencyElement := item.frequencyParent
+	var nextFrequencyAmount int
+	var nextFrequencyElement *Element[*FrequencyItem[K, V]]
+
+	if currentFrequencyElement == nil {
+		nextFrequencyAmount = 1
+		nextFrequencyElement = c.freqs.First()
+	} else {
+		atomicFrequencyItem := c.freqs.Value(currentFrequencyElement)
+		nextFrequencyAmount = atomicFrequencyItem.freq + 1
+		nextFrequencyElement = c.freqs.Next(currentFrequencyElement)
+	}
+
+	var nextFrequency *FrequencyItem[K, V]
+	if nextFrequencyElement != nil {
+		nextFrequency = c.freqs.Value(nextFrequencyElement)
+	}
+
+	if nextFrequencyElement == nil || nextFrequency == nil || nextFrequency.freq != nextFrequencyAmount {
+		newFrequencyItem := NewFrequencyItem[K, V]()
+		newFrequencyItem.freq = nextFrequencyAmount
+
+		if currentFrequencyElement == nil {
+			nextFrequencyElement = c.freqs.PushFront(newFrequencyItem)
+		} else {
+			nextFrequencyElement = c.freqs.InsertValueAfter(newFrequencyItem, currentFrequencyElement)
+		}
+	}
+
+	item.frequencyParent = nextFrequencyElement
+
+	nextFrequency = c.freqs.Value(nextFrequencyElement)
+	nextFrequency.entries.Set(item, struct{}{})
+
+	if currentFrequencyElement != nil {
+		c.remove(currentFrequencyElement, item)
+	}
+}
+
+func (c *Cache[K, V]) remove(listItem *Element[*FrequencyItem[K, V]], item *CacheItem[K, V]) {
+	entries := c.freqs.Value(listItem).entries
+
+	entries.Delete(item)
+	// if entries.Len() == 0 {
+	// 	c.freqs.Remove(listItem)
+	// }
+}
+
+func (c *Cache[K, V]) atCapacity() (bool, int) {
+	size, capacity := c.Size(), c.Capacity()
+	c.log("cache stats: %d/%d", size, capacity)
+	return size >= capacity, size - capacity
+}
+
+func (c *Cache[K, V]) evict(total int) error {
+	if total == 0 {
+		return nil
+	}
+
+	frequencyElement := c.freqs.First()
+	if frequencyElement == nil {
+		c.log("no frequency element")
+		return nil
+	}
+
+	for evicted := 0; evicted < total; {
+		c.log("running eviction: [to_evict:%d, evicted: %d]", total, evicted)
+
+		c.log("first frequency element %p", frequencyElement)
+
+		frequencyItem := c.freqs.Value(frequencyElement)
+		if frequencyItem == nil {
+			return nil
+		}
+
+		entries := frequencyItem.entries
+
+		if entries.Len() == 0 {
+			c.log("no frequency entries")
+			frequencyElement = c.freqs.Next(frequencyElement)
+			continue
+		}
+
+		var rangeErr error
+		entries.Range(func(key, v any) bool {
+			if evicted >= total {
+				c.log("evicted enough (%d >= %d), stopping", evicted, total)
+				return false
+			}
+
+			entry, _ := key.(*CacheItem[K, V])
+
+			if err := c.Delete(entry.key); err != nil {
+				if errors.Is(err, ErrNotFound) {
+					c.log("key '%s' not found", entry.key)
+					// Cleanup obsolete frequency
+					c.remove(frequencyElement, entry)
+					return true
+				}
+
+				rangeErr = errors.WithStack(err)
+				return false
+			}
+
+			c.log("evicted key '%v' (size: %d)", entry.key, entry.size)
+
+			evicted += int(entry.size)
+
+			return true
+		})
+		if rangeErr != nil {
+			return errors.WithStack(rangeErr)
+		}
+	}
+
+	return nil
+}
+
+func (c *Cache[K, V]) Evict() error {
+	exceed, delta := c.atCapacity()
+	if exceed && delta > 0 {
+		if err := c.evict(delta); err != nil {
+			return errors.WithStack(err)
+		}
+	}
+
+	return nil
+}
+
+func New[K comparable, V any](store Store[K, V], funcs ...OptionsFunc[K, V]) *Cache[K, V] {
+	opts := DefaultOptions[K, V](funcs...)
+
+	cache := &Cache[K, V]{
+		index:        NewMap[K, *CacheItem[K, V]](),
+		freqs:        NewList[*FrequencyItem[K, V]](),
+		capacity:     opts.Capacity,
+		store:        store,
+		getValueSize: opts.GetValueSize,
+		sync:         NewSynchronizer[K](),
+		log:          opts.Log,
+	}
+
+	return cache
+}

pkg/storage/driver/cache/lfu/expirable/cache.go

@@ -0,0 +1,17 @@
+package expirable
+
+import (
+	"time"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+)
+
+type Cache[K comparable, V any] struct {
+	ttl        time.Duration
+	cache      *lfu.Cache[K, V]
+	timestamps *lfu.Map[K, time.Duration]
+}
+
+func NewCache[K comparable, V any](cache *lfu.Cache[K, V], ttl time.Duration) *Cache[K, V] {
+	return &Cache[K, V]{}
+}

pkg/storage/driver/cache/lfu/fs/cache_test.go

@@ -0,0 +1,37 @@
+package fs
+
+import (
+	"bytes"
+	"io"
+	"path/filepath"
+	"testing"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu/testsuite"
+	"github.com/pkg/errors"
+)
+
+func TestCacheWithFSStore(t *testing.T) {
+	testsuite.TestCacheWithStore(t, func(testName string) lfu.Store[string, string] {
+		dir := filepath.Join("testdata", "testsuite", testName)
+		store := NewStore[string, string](dir,
+			WithMarshalValue[string, string](func(value string) (io.Reader, error) {
+				return bytes.NewBuffer([]byte(value)), nil
+			}),
+			WithUnmarshalValue[string, string](func(r io.Reader) (string, error) {
+				data, err := io.ReadAll(r)
+				if err != nil {
+					return "", errors.WithStack(err)
+				}
+
+				return string(data), nil
+			}),
+		)
+
+		if err := store.Clear(); err != nil {
+			panic(errors.WithStack(err))
+		}
+
+		return store
+	})
+}

pkg/storage/driver/cache/lfu/fs/hash.go

@@ -0,0 +1,19 @@
+package fs
+
+import (
+	"strconv"
+
+	"github.com/mitchellh/hashstructure/v2"
+	"github.com/pkg/errors"
+)
+
+func DefaultGetKeyHash[K comparable](key K) ([]string, error) {
+	uintHash, err := hashstructure.Hash(key, hashstructure.FormatV2, nil)
+	if err != nil {
+		return nil, errors.WithStack(err)
+	}
+
+	hash := strconv.FormatUint(uintHash, 16)
+
+	return []string{hash[0:2], hash[2:4], hash[2:4], hash}, nil
+}

pkg/storage/driver/cache/lfu/fs/marshal.go

@@ -0,0 +1,31 @@
+package fs
+
+import (
+	"bytes"
+	"encoding/gob"
+	"io"
+
+	"github.com/pkg/errors"
+)
+
+func DefaultMarshalValue[V any](value V) (io.Reader, error) {
+	var buf bytes.Buffer
+	encoder := gob.NewEncoder(&buf)
+
+	if err := encoder.Encode(value); err != nil {
+		return nil, errors.WithStack(err)
+	}
+
+	return &buf, nil
+}
+
+func DefaultUnmarshalValue[V any](d io.Reader) (V, error) {
+	var value V
+	encoder := gob.NewDecoder(d)
+
+	if err := encoder.Decode(&value); err != nil {
+		return *new(V), errors.WithStack(err)
+	}
+
+	return value, nil
+}

pkg/storage/driver/cache/lfu/fs/options.go

@@ -0,0 +1,45 @@
+package fs
+
+import "io"
+
+type GetKeyHashFunc[K comparable] func(key K) ([]string, error)
+type MarshalValueFunc[V any] func(value V) (io.Reader, error)
+type UnmarshalValueFunc[V any] func(r io.Reader) (V, error)
+
+type Options[K comparable, V any] struct {
+	GetKeyHash     GetKeyHashFunc[K]
+	MarshalValue   MarshalValueFunc[V]
+	UnmarshalValue UnmarshalValueFunc[V]
+}
+
+type OptionsFunc[K comparable, V any] func(opts *Options[K, V])
+
+func DefaultOptions[K comparable, V any](funcs ...OptionsFunc[K, V]) *Options[K, V] {
+	opts := &Options[K, V]{
+		GetKeyHash:     DefaultGetKeyHash[K],
+		MarshalValue:   DefaultMarshalValue[V],
+		UnmarshalValue: DefaultUnmarshalValue[V],
+	}
+	for _, fn := range funcs {
+		fn(opts)
+	}
+	return opts
+}
+
+func WithGetKeyHash[K comparable, V any](getKeyHash GetKeyHashFunc[K]) OptionsFunc[K, V] {
+	return func(opts *Options[K, V]) {
+		opts.GetKeyHash = getKeyHash
+	}
+}
+
+func WithMarshalValue[K comparable, V any](marshalValue MarshalValueFunc[V]) OptionsFunc[K, V] {
+	return func(opts *Options[K, V]) {
+		opts.MarshalValue = marshalValue
+	}
+}
+
+func WithUnmarshalValue[K comparable, V any](unmarshalValue UnmarshalValueFunc[V]) OptionsFunc[K, V] {
+	return func(opts *Options[K, V]) {
+		opts.UnmarshalValue = unmarshalValue
+	}
+}

pkg/storage/driver/cache/lfu/fs/store.go

@@ -0,0 +1,165 @@
+package fs
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"github.com/pkg/errors"
+)
+
+type Store[K comparable, V any] struct {
+	baseDir        string
+	getKeyHash     GetKeyHashFunc[K]
+	marshalValue   MarshalValueFunc[V]
+	unmarshalValue UnmarshalValueFunc[V]
+}
+
+// Delete implements Store.
+func (s *Store[K, V]) Delete(key K) error {
+	path, err := s.getEntryPath(key)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+// Get implements Store.
+func (s *Store[K, V]) Get(key K) (V, error) {
+	path, err := s.getEntryPath(key)
+	if err != nil {
+		return *new(V), errors.WithStack(err)
+	}
+
+	value, err := s.readValue(path)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return *new(V), errors.WithStack(lfu.ErrNotFound)
+		}
+
+		return *new(V), errors.WithStack(err)
+	}
+
+	return value, nil
+}
+
+// Set implements Store.
+func (s *Store[K, V]) Set(key K, value V) error {
+	path, err := s.getEntryPath(key)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := s.writeValue(path, value); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func (s *Store[K, V]) Clear() error {
+	if err := os.RemoveAll(s.baseDir); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func (s *Store[K, V]) getEntryPath(k K) (string, error) {
+	hash, err := s.getKeyHash(k)
+	if err != nil {
+		return "", errors.WithStack(err)
+	}
+
+	path := append([]string{s.baseDir}, hash...)
+	return filepath.Join(path...), nil
+}
+
+func (s *Store[K, V]) writeValue(path string, value V) error {
+	fi, err := os.Stat(path)
+	if err == nil && !fi.Mode().IsRegular() {
+		return fmt.Errorf("%s already exists and is not a regular file", path)
+	}
+
+	dir := filepath.Dir(path)
+
+	if err := os.MkdirAll(dir, 0750); err != nil {
+		return errors.WithStack(err)
+	}
+
+	f, err := os.CreateTemp(dir, filepath.Base(path)+".tmp")
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	tmpName := f.Name()
+	defer func() {
+		if err != nil {
+			f.Close()
+			os.Remove(tmpName)
+		}
+	}()
+
+	reader, err := s.marshalValue(value)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if _, err := io.Copy(f, reader); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := f.Sync(); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := f.Close(); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := os.Rename(tmpName, path); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func (s *Store[K, V]) readValue(path string) (V, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return *new(V), errors.WithStack(err)
+	}
+
+	defer func() {
+		if err := file.Close(); err != nil && !errors.Is(err, os.ErrClosed) {
+			panic(errors.WithStack(err))
+		}
+	}()
+
+	value, err := s.unmarshalValue(file)
+
+	if err != nil {
+		return *new(V), errors.WithStack(err)
+	}
+
+	return value, nil
+}
+
+func NewStore[K comparable, V any](baseDir string, funcs ...OptionsFunc[K, V]) *Store[K, V] {
+	opts := DefaultOptions[K, V](funcs...)
+	return &Store[K, V]{
+		baseDir:        baseDir,
+		getKeyHash:     opts.GetKeyHash,
+		unmarshalValue: opts.UnmarshalValue,
+		marshalValue:   opts.MarshalValue,
+	}
+}
+
+var _ lfu.Store[string, int] = &Store[string, int]{}

pkg/storage/driver/cache/lfu/fs/testdata/.gitignore

@@ -0,0 +1,2 @@
+*
+!.gitignore

pkg/storage/driver/cache/lfu/list.go

@@ -0,0 +1,203 @@
+package lfu
+
+import (
+	"sync/atomic"
+)
+
+type List[T any] struct {
+	root *Element[T]
+	len  atomic.Int32
+	sync *Synchronizer[*Element[T]]
+}
+
+func (l *List[T]) First() *Element[T] {
+	if l.Len() == 0 {
+		return nil
+	}
+
+	var next *Element[T]
+	l.sync.ReadTx(l.root, func(upgrade func(func())) error {
+		next = l.root.next
+		return nil
+	})
+
+	return next
+}
+
+func (l *List[T]) Last() *Element[T] {
+	if l.Len() == 0 {
+		return nil
+	}
+
+	var prev *Element[T]
+	l.sync.ReadTx(l.root, func(upgrade func(func())) error {
+		prev = l.root.prev
+		return nil
+	})
+
+	return prev
+}
+
+func (l *List[T]) Prev(e *Element[T]) *Element[T] {
+	var prev *Element[T]
+	l.sync.ReadTx(e, func(upgrade func(func())) error {
+		prev = e.prev
+		return nil
+	})
+
+	return prev
+}
+
+func (l *List[T]) Next(e *Element[T]) *Element[T] {
+	var next *Element[T]
+	l.sync.ReadTx(e, func(upgrade func(func())) error {
+		next = e.next
+		return nil
+	})
+
+	return next
+}
+
+func (l *List[T]) Value(e *Element[T]) T {
+	var value T
+	l.sync.ReadTx(e, func(upgrade func(func())) error {
+		value = e.value
+		return nil
+	})
+
+	return value
+}
+
+func (l *List[T]) PushFront(v T) *Element[T] {
+	return l.InsertValueAfter(v, l.root)
+}
+
+func (l *List[T]) PushBack(v T) *Element[T] {
+	return l.InsertValueAfter(v, l.root)
+}
+
+func (l *List[T]) Remove(e *Element[T]) {
+	l.remove(e)
+}
+
+func (l *List[T]) Len() int {
+	return int(l.len.Load())
+}
+
+func (l *List[T]) insertAfter(e *Element[T], at *Element[T]) *Element[T] {
+	l.sync.ReadTx(e, func(upgrade func(fn func())) error {
+		var next *Element[T]
+		l.sync.ReadTx(at, func(upgrade func(func())) error {
+			next = at.next
+			return nil
+		})
+
+		upgrade(func() {
+			e.prev = at
+			e.next = next
+			e.list = l
+		})
+
+		if e.prev != nil {
+			l.sync.WriteTx(e.prev, func() error {
+				e.prev.next = e
+				return nil
+			})
+		}
+
+		if e.next != nil {
+			l.sync.WriteTx(e.next, func() error {
+				e.next.prev = e
+				return nil
+			})
+		}
+
+		return nil
+	})
+
+	l.len.Add(1)
+
+	return e
+}
+
+func (l *List[T]) InsertValueAfter(v T, at *Element[T]) *Element[T] {
+	e := NewElement[T](v)
+	return l.insertAfter(e, at)
+}
+
+func (l *List[T]) remove(e *Element[T]) {
+	if e == nil && e == l.root {
+		return
+	}
+
+	l.sync.ReadTx(e, func(upgrade func(fn func())) error {
+		if e.prev != nil {
+			if e.prev == e {
+				upgrade(func() {
+					e.prev.next = e.next
+				})
+			} else {
+				l.sync.WriteTx(e.prev, func() error {
+					e.prev.next = e.next
+					return nil
+				})
+			}
+		}
+
+		if e.next != nil {
+			if e.next == e {
+				upgrade(func() {
+					e.next.prev = e.prev
+				})
+			} else {
+				l.sync.WriteTx(e.next, func() error {
+					e.next.prev = e.prev
+					return nil
+				})
+			}
+		}
+
+		upgrade(func() {
+			e.next = nil
+			e.prev = nil
+			e.list = nil
+		})
+
+		return nil
+	})
+
+	l.sync.Remove(e)
+	l.len.Add(-1)
+}
+
+func NewList[T any]() *List[T] {
+	root := NewElement(*new(T))
+	root.next = root
+	root.prev = root
+
+	list := &List[T]{
+		sync: NewSynchronizer[*Element[T]](),
+	}
+
+	root.list = list
+	list.root = root
+
+	return list
+}
+
+type Element[T any] struct {
+	prev  *Element[T]
+	next  *Element[T]
+	list  *List[T]
+	value T
+}
+
+func NewElement[T any](v T) *Element[T] {
+	element := &Element[T]{
+		prev:  nil,
+		next:  nil,
+		list:  nil,
+		value: v,
+	}
+	return element
+}

pkg/storage/driver/cache/lfu/map.go

@@ -0,0 +1,67 @@
+package lfu
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+type Map[K comparable, V any] struct {
+	size  atomic.Int32
+	inner sync.Map
+}
+
+func (m *Map[K, V]) Get(key K) (V, bool) {
+	raw, exists := m.inner.Load(key)
+	if !exists {
+		return *new(V), false
+	}
+
+	value, ok := raw.(V)
+	if !ok {
+		return *new(V), false
+	}
+
+	return value, true
+}
+
+func (m *Map[K, V]) GetOrSet(key K, defaultValue V) (V, bool) {
+	raw, loaded := m.inner.LoadOrStore(key, defaultValue)
+	if !loaded {
+		m.size.Add(1)
+	}
+
+	value, ok := raw.(V)
+	if !ok {
+		return *new(V), loaded
+	}
+
+	return value, loaded
+}
+
+func (m *Map[K, V]) Set(key K, value V) {
+	_, loaded := m.inner.Swap(key, value)
+	if !loaded {
+		m.size.Add(1)
+	}
+}
+
+func (m *Map[K, V]) Delete(key K) {
+	_, existed := m.inner.LoadAndDelete(key)
+	if existed {
+		m.size.Add(-1)
+	}
+}
+
+func (m *Map[K, V]) Range(fn func(key, value any) bool) {
+	m.inner.Range(fn)
+}
+
+func (m *Map[K, V]) Len() int {
+	return int(m.size.Load())
+}
+
+func NewMap[K comparable, V any]() *Map[K, V] {
+	return &Map[K, V]{
+		inner: sync.Map{},
+	}
+}

pkg/storage/driver/cache/lfu/memory/cache_test.go

@@ -0,0 +1,14 @@
+package memory
+
+import (
+	"testing"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu/testsuite"
+)
+
+func TestCacheWithMemoryStore(t *testing.T) {
+	testsuite.TestCacheWithStore(t, func(testName string) lfu.Store[string, string] {
+		return NewStore[string, string]()
+	})
+}

pkg/storage/driver/cache/lfu/memory/memory.go

@@ -0,0 +1,40 @@
+package memory
+
+import (
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"github.com/pkg/errors"
+)
+
+type Store[K comparable, V any] struct {
+	index *lfu.Map[K, V]
+}
+
+// Delete implements Store.
+func (s *Store[K, V]) Delete(key K) error {
+	s.index.Delete(key)
+	return nil
+}
+
+// Get implements Store.
+func (s *Store[K, V]) Get(key K) (V, error) {
+	value, exists := s.index.Get(key)
+	if !exists {
+		return *new(V), errors.WithStack(lfu.ErrNotFound)
+	}
+
+	return value, nil
+}
+
+// Set implements Store.
+func (s *Store[K, V]) Set(key K, value V) error {
+	s.index.Set(key, value)
+	return nil
+}
+
+func NewStore[K comparable, V any]() *Store[K, V] {
+	return &Store[K, V]{
+		index: lfu.NewMap[K, V](),
+	}
+}
+
+var _ lfu.Store[string, int] = &Store[string, int]{}

pkg/storage/driver/cache/lfu/options.go

@@ -0,0 +1,47 @@
+package lfu
+
+type GetValueSizeFunc[V any] func(value V) (int, error)
+
+type LogFunc func(format string, values ...any)
+
+func DefaultLogFunc(format string, values ...any) {
+
+}
+
+type Options[K comparable, V any] struct {
+	GetValueSize GetValueSizeFunc[V]
+	Capacity     int
+	Log          LogFunc
+}
+
+type OptionsFunc[K comparable, V any] func(opts *Options[K, V])
+
+func DefaultOptions[K comparable, V any](funcs ...OptionsFunc[K, V]) *Options[K, V] {
+	opts := &Options[K, V]{
+		GetValueSize: DefaultGetValueSize[V],
+		Capacity:     100,
+		Log:          DefaultLogFunc,
+	}
+	for _, fn := range funcs {
+		fn(opts)
+	}
+	return opts
+}
+
+func WithCapacity[K comparable, V any](capacity int) OptionsFunc[K, V] {
+	return func(opts *Options[K, V]) {
+		opts.Capacity = capacity
+	}
+}
+
+func WithGetValueSize[K comparable, V any](getValueSize GetValueSizeFunc[V]) OptionsFunc[K, V] {
+	return func(opts *Options[K, V]) {
+		opts.GetValueSize = getValueSize
+	}
+}
+
+func WithLog[K comparable, V any](fn LogFunc) OptionsFunc[K, V] {
+	return func(opts *Options[K, V]) {
+		opts.Log = fn
+	}
+}

pkg/storage/driver/cache/lfu/size.go

@@ -0,0 +1,41 @@
+package lfu
+
+import (
+	"github.com/pkg/errors"
+)
+
+type Measurable interface {
+	Size() (int, error)
+}
+
+func DefaultGetValueSize[V any](value V) (int, error) {
+	switch v := any(value).(type) {
+	case int:
+		return v, nil
+	case int8:
+		return int(v), nil
+	case int32:
+		return int(v), nil
+	case int64:
+		return int(v), nil
+	case float32:
+		return int(v), nil
+	case float64:
+		return int(v), nil
+	case []byte:
+		return len(v), nil
+	case string:
+		return len(v), nil
+	}
+
+	if measurable, ok := any(value).(Measurable); ok {
+		size, err := measurable.Size()
+		if err != nil {
+			return 0, errors.WithStack(err)
+		}
+
+		return size, nil
+	}
+
+	return 0, errors.Errorf("could not retrieve size of type '%T'", value)
+}

pkg/storage/driver/cache/lfu/store.go

@@ -0,0 +1,7 @@
+package lfu
+
+type Store[K comparable, V any] interface {
+	Delete(key K) error
+	Set(key K, value V) error
+	Get(key K) (V, error)
+}

pkg/storage/driver/cache/lfu/synchronizer.go

@@ -0,0 +1,56 @@
+package lfu
+
+import (
+	"sync"
+
+	"github.com/pkg/errors"
+)
+
+type Synchronizer[K comparable] struct {
+	index *Map[K, *sync.RWMutex]
+}
+
+func (s *Synchronizer[K]) Remove(key K) {
+	s.index.Delete(key)
+}
+
+func (s *Synchronizer[K]) ReadTx(key K, fn func(upgrade func(fn func())) error) error {
+	mutex, _ := s.index.GetOrSet(key, &sync.RWMutex{})
+	mutex.RLock()
+	defer mutex.RUnlock()
+
+	upgrade := func(fn func()) {
+		mutex.RUnlock()
+		mutex.Lock()
+		defer func() {
+			mutex.Unlock()
+			mutex.RLock()
+		}()
+
+		fn()
+	}
+
+	if err := fn(upgrade); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func (s *Synchronizer[K]) WriteTx(key K, fn func() error) error {
+	mutex, _ := s.index.GetOrSet(key, &sync.RWMutex{})
+	mutex.Lock()
+	defer mutex.Unlock()
+
+	if err := fn(); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func NewSynchronizer[K comparable]() *Synchronizer[K] {
+	return &Synchronizer[K]{
+		index: NewMap[K, *sync.RWMutex](),
+	}
+}

pkg/storage/driver/cache/lfu/testsuite/main.go

@@ -0,0 +1,40 @@
+package testsuite
+
+import (
+	"reflect"
+	"runtime"
+	"strings"
+	"testing"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"github.com/pkg/errors"
+)
+
+type StoreFactory func(testName string) lfu.Store[string, string]
+type testCase func(t *testing.T, store lfu.Store[string, string]) error
+
+var testCases = []testCase{
+	testSetGetDelete,
+	testEviction,
+	testConcurrent,
+	testMultipleSet,
+}
+
+func TestCacheWithStore(t *testing.T, factory StoreFactory) {
+	for _, tc := range testCases {
+		funcName := runtime.FuncForPC(reflect.ValueOf(tc).Pointer()).Name()
+		funcNameParts := strings.Split(funcName, "/")
+		testName := funcNameParts[len(funcNameParts)-1]
+		func(tc testCase) {
+			t.Run(testName, func(t *testing.T) {
+				t.Parallel()
+
+				store := factory(testName)
+
+				if err := tc(t, store); err != nil {
+					t.Fatalf("%+v", errors.WithStack(err))
+				}
+			})
+		}(tc)
+	}
+}

pkg/storage/driver/cache/lfu/testsuite/test_concurrent.go

@@ -0,0 +1,67 @@
+package testsuite
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"github.com/pkg/errors"
+)
+
+func testConcurrent(t *testing.T, store lfu.Store[string, string]) error {
+	const value = "foobar"
+	totalKeys := 25
+	totalSize := len(value) * totalKeys
+	capacity := totalSize / 2
+
+	cache := lfu.New[string, string](store,
+		lfu.WithCapacity[string, string](capacity),
+		lfu.WithLog[string, string](t.Logf),
+	)
+
+	var wg sync.WaitGroup
+
+	wg.Add(totalKeys)
+
+	loops := totalKeys * 10
+
+	for i := 0; i < totalKeys; i++ {
+		key := fmt.Sprintf("key%d", i)
+		func(key string) {
+			go func() {
+				defer wg.Done()
+				for i := 0; i < loops; i++ {
+					if err := cache.Set(key, value); err != nil {
+						t.Errorf("%+v", errors.WithStack(err))
+					}
+				}
+			}()
+		}(key)
+	}
+
+	wg.Wait()
+
+	t.Logf("cache before final evict [capacity: %d, size: %d, len: %d]", cache.Capacity(), cache.Size(), cache.Len())
+
+	if err := cache.Evict(); err != nil {
+		t.Errorf("%+v", errors.WithStack(err))
+	}
+
+	t.Logf("cache after final evict [capacity: %d, size: %d, len: %d]", cache.Capacity(), cache.Size(), cache.Len())
+
+	expectedLength := capacity / len(value)
+	if e, g := expectedLength, cache.Len(); e < g {
+		t.Errorf("cache.Len(): expected <= %d, got %d", e, g)
+	}
+
+	if cache.Size() > capacity {
+		t.Errorf("cache.Size(): expected <= %d, got %d", capacity, cache.Size())
+	}
+
+	if e, g := expectedLength*len(value), cache.Size(); e < g {
+		t.Errorf("cache.Size(): expected <= %d, got %d", e, g)
+	}
+
+	return nil
+}

pkg/storage/driver/cache/lfu/testsuite/test_eviction.go

@@ -0,0 +1,56 @@
+package testsuite
+
+import (
+	"testing"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"github.com/pkg/errors"
+)
+
+func testEviction(t *testing.T, store lfu.Store[string, string]) error {
+	cache := lfu.New[string, string](store,
+		lfu.WithCapacity[string, string](10),
+		lfu.WithLog[string, string](t.Logf),
+	)
+
+	if err := cache.Set("key1", "key1"); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := cache.Set("key2", "key2"); err != nil {
+		return errors.WithStack(err)
+	}
+
+	// Increment frequency of key2
+	if _, err := cache.Get("key2"); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := 8, cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	if err := cache.Set("key3", "key3"); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := cache.Set("key3", "key3"); err != nil {
+		return errors.WithStack(err)
+	}
+
+	t.Logf("cache [capacity: %d, size: %d, len: %d]", cache.Capacity(), cache.Size(), cache.Len())
+
+	if e, g := cache.Capacity(), cache.Size(); e < g {
+		t.Errorf("cache.Size(): expected <= %d, got %d", e, g)
+	}
+
+	if e, g := 2, cache.Len(); e != g {
+		t.Errorf("cache.Len(): expected %d, got %d", e, g)
+	}
+
+	if cache.Size() < 0 {
+		t.Errorf("cache.Size(): expected value >= 0, got %d", cache.Size())
+	}
+
+	return nil
+}

pkg/storage/driver/cache/lfu/testsuite/test_multiple_set.go

@@ -0,0 +1,80 @@
+package testsuite
+
+import (
+	"testing"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"github.com/pkg/errors"
+)
+
+func testMultipleSet(t *testing.T, store lfu.Store[string, string]) error {
+	const (
+		key         = "mykey"
+		firstValue  = "foo"
+		secondValue = "bar"
+		thirdValue  = "foobar"
+	)
+
+	cache := lfu.New[string, string](store)
+
+	if e, g := 0, cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	if err := cache.Set(key, firstValue); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := len(firstValue), cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	retrieved, err := cache.Get(key)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := firstValue, retrieved; e != g {
+		t.Errorf("cache.Get(key): expected '%v', got '%v'", e, g)
+	}
+
+	if err := cache.Set(key, secondValue); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := len(secondValue), cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	retrieved, err = cache.Get(key)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := secondValue, retrieved; e != g {
+		t.Errorf("cache.Get(key): expected '%v', got '%v'", e, g)
+	}
+
+	if err := cache.Set(key, thirdValue); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := len(thirdValue), cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	retrieved, err = cache.Get(key)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := thirdValue, retrieved; e != g {
+		t.Errorf("cache.Get(key): expected '%v', got '%v'", e, g)
+	}
+
+	if e, g := len(thirdValue), cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	return nil
+}

pkg/storage/driver/cache/lfu/testsuite/test_set_get_delete.go

@@ -0,0 +1,66 @@
+package testsuite
+
+import (
+	"testing"
+
+	"forge.cadoles.com/arcad/edge/pkg/storage/driver/cache/lfu"
+	"github.com/pkg/errors"
+)
+
+func testSetGetDelete(t *testing.T, store lfu.Store[string, string]) error {
+	const (
+		key   = "mykey"
+		value = "foobar"
+	)
+
+	cache := lfu.New[string, string](store, lfu.WithCapacity[string, string](10))
+
+	if e, g := 0, cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	if err := cache.Set(key, value); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := len(value), cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	if e, g := 1, cache.Len(); e != g {
+		t.Errorf("cache.Len(): expected '%v', got '%v'", e, g)
+	}
+
+	retrieved, err := cache.Get(key)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if e, g := value, retrieved; e != g {
+		t.Errorf("cache.Get(key): expected '%v', got '%v'", e, g)
+	}
+
+	if err := cache.Delete(key); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if _, err := cache.Get(key); err == nil || !errors.Is(err, lfu.ErrNotFound) {
+		t.Errorf("cache.Get(key): err should be lfu.ErrNotFound, got '%v'", errors.WithStack(err))
+	}
+
+	if e, g := value, retrieved; e != g {
+		t.Errorf("cache.Get(key): expected '%v', got '%v'", e, g)
+	}
+
+	if e, g := 0, cache.Size(); e != g {
+		t.Errorf("cache.Size(): expected '%v', got '%v'", e, g)
+	}
+
+	if e, g := 0, cache.Len(); e != g {
+		t.Errorf("cache.Len(): expected '%v', got '%v'", e, g)
+	}
+
+	t.Logf("cache [capacity: %d, size: %d, len: %d]", cache.Capacity(), cache.Size(), cache.Len())
+
+	return nil
+}