/
cache.go
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/
cache.go
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// @author Couchbase <info@couchbase.com>
// @copyright 2016 Couchbase, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License 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 main
import (
"container/list"
"errors"
"sync"
)
const (
MaxCacheSize = 1024
)
var (
ErrKeyNotFound = errors.New("Key not found")
)
type item struct {
key string
value string
lruElem *list.Element
}
type Cache struct {
mu *sync.Mutex
lru *list.List
items map[string]*item
maxSize int
}
func NewCache() *Cache {
return &Cache{
mu: &sync.Mutex{},
lru: list.New(),
items: make(map[string]*item),
maxSize: MaxCacheSize,
}
}
func (c *Cache) Get(key string) (string, error) {
c.mu.Lock()
defer c.mu.Unlock()
itm, ok := c.items[key]
if !ok {
return "", ErrKeyNotFound
}
return itm.value, nil
}
func (c *Cache) Set(key string, value string) {
c.mu.Lock()
defer c.mu.Unlock()
itm, ok := c.items[key]
if !ok {
c.create(key, value)
return
}
itm.value = value
c.touch(itm)
}
func (c *Cache) maybeEvict() {
if len(c.items) < c.maxSize {
return
}
victim := c.lru.Remove(c.lru.Front()).(*item)
delete(c.items, victim.key)
}
func (c *Cache) create(key string, value string) {
c.maybeEvict()
itm := &item{
key: key,
value: value,
}
itm.lruElem = c.lru.PushBack(itm)
c.items[key] = itm
}
func (c *Cache) touch(itm *item) {
c.lru.MoveToBack(itm.lruElem)
}