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lru_cache.go
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lru_cache.go
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// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"). You may
// not use this file except in compliance with the License. A copy of the
// License is located at
//
// http://aws.amazon.com/apache2.0/
//
// or in the "license" file accompanying this file. This file is distributed
// on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
// express or implied. See the License for the specific language governing
// permissions and limitations under the License.
package async
import (
"container/list"
"sync"
"time"
)
type Cache interface {
// Get fetches a value from cache, returns nil, false on miss
Get(key string) (Value, bool)
// Set sets a value in cache. overrites any existing value
Set(key string, value Value)
// Delete deletes the value from the cache
Delete(key string)
}
// Creates an LRUCache with maximum size, ttl for items.
func NewLRUCache(size int, ttl time.Duration) Cache {
lru := &lruCache{size: size,
ttl: ttl,
cache: make(map[string]*entry),
evictList: list.New(),
}
return lru
}
type Value interface{}
type entry struct {
value Value
added time.Time
}
type lruCache struct {
sync.Mutex
cache map[string]*entry
evictList *list.List
size int
ttl time.Duration
}
// Get returns the value associated with the key
func (lru *lruCache) Get(key string) (Value, bool) {
lru.Lock()
defer lru.Unlock()
entry, ok := lru.cache[key]
if !ok {
return nil, false
}
ok = lru.evictStale(entry, key)
if !ok {
return nil, false
}
lru.updateAccessed(key)
return entry.value, true
}
// Set sets the key-value pair in the cache
func (lru *lruCache) Set(key string, value Value) {
lru.Lock()
defer lru.Unlock()
lru.cache[key] = &entry{value: value, added: time.Now()}
// Remove from the evict list if an entry already existed
lru.removeFromEvictList(key)
lru.evictList.PushBack(key)
lru.purgeSize()
}
// Delete removes the entry associated with the key from cache
func (lru *lruCache) Delete(key string) {
lru.Lock()
defer lru.Unlock()
lru.removeFromEvictList(key)
delete(lru.cache, key)
}
func (lru *lruCache) updateAccessed(key string) {
// update evict list
for elem := lru.evictList.Front(); elem != nil; elem = elem.Next() {
if elem.Value == key {
lru.evictList.MoveToBack(elem)
break
}
}
}
func (lru *lruCache) removeFromEvictList(key string) {
var next *list.Element
for element := lru.evictList.Front(); element != nil; element = next {
next = element.Next()
if element.Value == key {
lru.evictList.Remove(element)
break
}
}
}
func (lru *lruCache) evictStale(entry *entry, key string) bool {
if time.Since(entry.added) >= lru.ttl {
// remove from evict list
for elem := lru.evictList.Front(); elem != nil; elem = elem.Next() {
if elem.Value == key {
lru.evictList.Remove(elem)
break
}
}
// delete from cache
delete(lru.cache, key)
return false
}
return true
}
func (lru *lruCache) purgeSize() {
for elem := lru.evictList.Front(); elem != nil; elem = elem.Next() {
if len(lru.cache) <= lru.size {
break
}
key := elem.Value.(string)
// remove from list
lru.evictList.Remove(elem)
// delete from cache
delete(lru.cache, key)
}
}