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lfu.go
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lfu.go
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package lfu
import (
"container/list"
"sync"
)
type Eviction struct {
Key string
Value interface{}
}
type Cache struct {
// If len > UpperBound, cache will automatically evict
// down to LowerBound. If either value is 0, this behavior
// is disabled.
UpperBound int
LowerBound int
values map[string]*cacheEntry
freqs *list.List
len int
lock *sync.Mutex
EvictionChannel chan<- Eviction
}
type cacheEntry struct {
key string
value interface{}
freqNode *list.Element
}
type listEntry struct {
entries map[*cacheEntry]byte
freq int
}
func New() *Cache {
c := new(Cache)
c.values = make(map[string]*cacheEntry)
c.freqs = list.New()
c.lock = new(sync.Mutex)
return c
}
func (c *Cache) Get(key string) interface{} {
c.lock.Lock()
defer c.lock.Unlock()
if e, ok := c.values[key]; ok {
c.increment(e)
return e.value
}
return nil
}
func (c *Cache) Set(key string, value interface{}) {
c.lock.Lock()
defer c.lock.Unlock()
if e, ok := c.values[key]; ok {
// value already exists for key. overwrite
e.value = value
c.increment(e)
} else {
// value doesn't exist. insert
e := new(cacheEntry)
e.key = key
e.value = value
c.values[key] = e
c.increment(e)
c.len++
// bounds mgmt
if c.UpperBound > 0 && c.LowerBound > 0 {
if c.len > c.UpperBound {
c.evict(c.len - c.LowerBound)
}
}
}
}
func (c *Cache) Len() int {
c.lock.Lock()
defer c.lock.Unlock()
return c.len
}
func (c *Cache) Evict(count int) int {
c.lock.Lock()
defer c.lock.Unlock()
return c.evict(count)
}
func (c *Cache) evict(count int) int {
// No lock here so it can be called
// from within the lock (during Set)
var evicted int
for i := 0; i < count; {
if place := c.freqs.Front(); place != nil {
for entry, _ := range place.Value.(*listEntry).entries {
if i < count {
if c.EvictionChannel != nil {
c.EvictionChannel <- Eviction{
Key: entry.key,
Value: entry.value,
}
}
delete(c.values, entry.key)
c.remEntry(place, entry)
evicted++
c.len--
i++
}
}
}
}
return evicted
}
func (c *Cache) increment(e *cacheEntry) {
currentPlace := e.freqNode
var nextFreq int
var nextPlace *list.Element
if currentPlace == nil {
// new entry
nextFreq = 1
nextPlace = c.freqs.Front()
} else {
// move up
nextFreq = currentPlace.Value.(*listEntry).freq + 1
nextPlace = currentPlace.Next()
}
if nextPlace == nil || nextPlace.Value.(*listEntry).freq != nextFreq {
// create a new list entry
li := new(listEntry)
li.freq = nextFreq
li.entries = make(map[*cacheEntry]byte)
if currentPlace != nil {
nextPlace = c.freqs.InsertAfter(li, currentPlace)
} else {
nextPlace = c.freqs.PushFront(li)
}
}
e.freqNode = nextPlace
nextPlace.Value.(*listEntry).entries[e] = 1
if currentPlace != nil {
// remove from current position
c.remEntry(currentPlace, e)
}
}
func (c *Cache) remEntry(place *list.Element, entry *cacheEntry) {
entries := place.Value.(*listEntry).entries
delete(entries, entry)
if len(entries) == 0 {
c.freqs.Remove(place)
}
}