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|
package cache
import (
"bytes"
"hash/fnv"
"iter"
"sync"
"time"
)
func zero[T any]() T {
var ret T
return ret
}
type Map[K any, V any] interface {
Set(key K, value V, ttl time.Duration) error
Get(key K) (V, time.Duration, error)
Delete(key K) error
Clear() iter.Seq2[K, V]
}
type Node struct {
Hash uint64
Expiration time.Time
Access uint64
Key []byte
Value []byte
HashNext *Node
HashPrev *Node
EvictNext *Node
EvictPrev *Node
}
type Store struct {
bucket []Node
lenght uint64
cost uint64
evict Node
max_cost uint64
strategy EvictionStrategies
mu sync.RWMutex
}
func (s *Store) Clear() {
s.mu.Lock()
defer s.mu.Unlock()
s.bucket = make([]Node, 8)
s.lenght = 0
s.cost = 0
s.evict.EvictNext = &s.evict
s.evict.EvictPrev = &s.evict
}
func hash(data []byte) uint64 {
hasher := fnv.New64()
if _, err := hasher.Write(data); err != nil {
panic(err)
}
return hasher.Sum64()
}
func lookup(s *Store, key []byte) (uint64, uint64) {
hash := hash(key)
return hash % uint64(len(s.bucket)), hash
}
func lazyInitBucket(n *Node) {
if n.HashNext == nil {
n.HashNext = n
n.HashPrev = n
}
}
func (s *Store) Get(key []byte) ([]byte, time.Duration, bool) {
s.mu.RLock()
defer s.mu.RUnlock()
idx, _ := lookup(s, key)
bucket := &s.bucket[idx]
lazyInitBucket(bucket)
for v := bucket.HashNext; v != bucket; v = v.HashNext {
if bytes.Equal(key, v.Key) {
s.strategy.OnAccess(v)
return v.Value, 0, true
}
}
return nil, 0, false
}
func resize(s *Store) {
bucket := make([]Node, 2*len(s.bucket))
for v := s.evict.EvictNext; v != &s.evict; v = v.EvictNext {
idx := v.Hash % uint64(len(bucket))
n := &bucket[idx]
lazyInitBucket(n)
v.HashPrev = n
v.HashNext = v.HashPrev.HashNext
v.HashNext.HashPrev = v
v.HashPrev.HashNext = v
}
s.bucket = bucket
}
func (s *Store) Set(key []byte, value []byte, ttl time.Duration) {
s.mu.Lock()
defer s.mu.Unlock()
idx, hash := lookup(s, key)
bucket := &s.bucket[idx]
lazyInitBucket(bucket)
for v := bucket.HashNext; v != bucket; v = v.HashNext {
if bytes.Equal(key, v.Key) {
s.cost = s.cost + uint64(len(value)) - uint64(len(v.Value))
v.Value = value
v.Expiration = time.Now().Add(ttl)
s.strategy.OnAccess(v)
}
}
if float64(s.lenght)/float64(len(s.bucket)) > 0.75 {
resize(s)
//resize may invidate pointer to bucket
bucket = &s.bucket[idx]
lazyInitBucket(bucket)
}
node := &Node{
Hash: hash,
Key: key,
Value: value,
Expiration: time.Now().Add(ttl),
}
node.HashPrev = bucket
node.HashNext = node.HashPrev.HashNext
node.HashNext.HashPrev = node
node.HashPrev.HashNext = node
s.strategy.OnInsert(node)
s.strategy.OnAccess(node)
s.cost = s.cost + uint64(len(key)) + uint64(len(value))
s.lenght = s.lenght + 1
}
func (s *Store) Delete(key []byte) bool {
s.mu.Lock()
defer s.mu.Unlock()
idx, _ := lookup(s, key)
bucket := &s.bucket[idx]
lazyInitBucket(bucket)
for v := bucket.HashNext; v != bucket; v = v.HashNext {
if bytes.Equal(key, v.Key) {
v.HashNext.HashPrev = v.HashPrev
v.HashPrev.HashNext = v.HashNext
v.HashNext = nil
v.HashPrev = nil
v.EvictNext.EvictPrev = v.EvictPrev
v.EvictPrev.EvictNext = v.EvictNext
v.EvictNext = nil
v.EvictPrev = nil
s.cost = s.cost - (uint64(len(v.Key)) + uint64(len(v.Value)))
s.lenght = s.lenght - 1
return true
}
}
return false
}
func (s *Store) Cost() uint64 {
return s.cost
}
|
