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cache.go
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cache.go
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/*
Cache.go is released under the MIT License <http://www.opensource.org/licenses/mit-license.php
Copyright (C) ITsysCOM GmbH. All Rights Reserved.
A LRU cache with TTL capabilities.
Original ideas from golang groupcache/lru.go
*/
package ltcache
import (
"container/list"
"strings"
"sync"
"time"
)
const (
UnlimitedCaching = -1
DisabledCaching = 0
)
type cachedItem struct {
itemID string
value interface{}
expiryTime time.Time
groupIDs []string // list of group this item belongs to
}
// Cache is an LRU/TTL cache. It is safe for concurrent access.
type Cache struct {
sync.RWMutex
// cache holds the items
cache map[string]*cachedItem
groups map[string]map[string]struct{} // map[groupID]map[itemKey]struct{}
// onEvicted will execute specific function if defined when an item will be removed
onEvicted func(itmID string, value interface{})
// maxEntries represents maximum number of entries allowed by LRU cache mechanism
// -1 for unlimited caching, 0 for disabling caching
maxEntries int
// ttl represents the lifetime of an cachedItem
ttl time.Duration
// staticTTL prevents expiryTime to be modified on key get/set
staticTTL bool
lruIdx *list.List
lruRefs map[string]*list.Element // index the list element based on it's key in cache
ttlIdx *list.List
ttlRefs map[string]*list.Element // index the list element based on it' key in cache
}
// New initializes a new cache.
func NewCache(maxEntries int, ttl time.Duration, staticTTL bool,
onEvicted func(itmID string, value interface{})) (c *Cache) {
c = &Cache{
cache: make(map[string]*cachedItem),
groups: make(map[string]map[string]struct{}),
onEvicted: onEvicted,
maxEntries: maxEntries,
ttl: ttl,
staticTTL: staticTTL,
lruIdx: list.New(),
lruRefs: make(map[string]*list.Element),
ttlIdx: list.New(),
ttlRefs: make(map[string]*list.Element),
}
if c.ttl > 0 {
go c.cleanExpired()
}
return
}
// Get looks up a key's value from the cache
func (c *Cache) Get(itmID string) (value interface{}, ok bool) {
c.Lock()
defer c.Unlock()
ci, has := c.cache[itmID]
if !has {
return
}
value, ok = ci.value, true
if c.maxEntries != UnlimitedCaching { // update lru indexes
c.lruIdx.MoveToFront(c.lruRefs[itmID])
}
if c.ttl > 0 && !c.staticTTL { // update ttl indexes
ci.expiryTime = time.Now().Add(c.ttl)
c.ttlIdx.MoveToFront(c.ttlRefs[itmID])
}
return
}
func (c *Cache) GetItemExpiryTime(itmID string) (exp time.Time, ok bool) {
c.RLock()
defer c.RUnlock()
var ci *cachedItem
ci, ok = c.cache[itmID]
if !ok {
return
}
exp = ci.expiryTime
return
}
func (c *Cache) HasItem(itmID string) (has bool) {
c.RLock()
_, has = c.cache[itmID]
c.RUnlock()
return
}
// Set sets/adds a value to the cache.
func (c *Cache) Set(itmID string, value interface{}, grpIDs []string) {
if c.maxEntries == DisabledCaching {
return
}
c.Lock()
defer c.Unlock()
now := time.Now()
if ci, ok := c.cache[itmID]; ok {
ci.value = value
c.remItemFromGroups(itmID, ci.groupIDs)
ci.groupIDs = grpIDs
c.addItemToGroups(itmID, grpIDs)
if c.maxEntries != UnlimitedCaching { // update lru indexes
c.lruIdx.MoveToFront(c.lruRefs[itmID])
}
if c.ttl > 0 && !c.staticTTL { // update ttl indexes
ci.expiryTime = now.Add(c.ttl)
c.ttlIdx.MoveToFront(c.ttlRefs[itmID])
}
return
}
ci := &cachedItem{itemID: itmID, value: value, groupIDs: grpIDs}
c.cache[itmID] = ci
c.addItemToGroups(itmID, grpIDs)
if c.maxEntries != UnlimitedCaching {
c.lruRefs[itmID] = c.lruIdx.PushFront(ci)
}
if c.ttl > 0 {
ci.expiryTime = now.Add(c.ttl)
c.ttlRefs[itmID] = c.ttlIdx.PushFront(ci)
}
if c.maxEntries != UnlimitedCaching {
var lElm *list.Element
if c.lruIdx.Len() > c.maxEntries {
lElm = c.lruIdx.Back()
}
if lElm != nil {
c.remove(lElm.Value.(*cachedItem).itemID)
}
}
}
// Remove removes the provided key from the cache.
func (c *Cache) Remove(itmID string) {
c.Lock()
c.remove(itmID)
c.Unlock()
}
// GetItemIDs returns a list of items matching prefix
func (c *Cache) GetItemIDs(prfx string) (itmIDs []string) {
c.RLock()
for itmID := range c.cache {
if strings.HasPrefix(itmID, prfx) {
itmIDs = append(itmIDs, itmID)
}
}
c.RUnlock()
return
}
// GroupLength returns the length of a group
func (c *Cache) GroupLength(grpID string) int {
c.RLock()
defer c.RUnlock()
return len(c.groups[grpID])
}
func (c *Cache) getGroupItemIDs(grpID string) (itmIDs []string) {
for itmID := range c.groups[grpID] {
itmIDs = append(itmIDs, itmID)
}
return
}
func (c *Cache) GetGroupItemIDs(grpID string) (itmIDs []string) {
c.RLock()
itmIDs = c.getGroupItemIDs(grpID)
c.RUnlock()
return
}
func (c *Cache) HasGroup(grpID string) (has bool) {
c.RLock()
_, has = c.groups[grpID]
c.RUnlock()
return
}
func (c *Cache) GetGroupItems(grpID string) (itms []interface{}) {
for _, itmID := range c.GetGroupItemIDs(grpID) {
itm, _ := c.Get(itmID)
itms = append(itms, itm)
}
return
}
func (c *Cache) RemoveGroup(grpID string) {
c.Lock()
for itmID := range c.groups[grpID] {
c.remove(itmID)
}
c.Unlock()
}
// remove completely removes an Element from the cache
func (c *Cache) remove(itmID string) {
ci, has := c.cache[itmID]
if !has {
return
}
if c.maxEntries != UnlimitedCaching {
c.lruIdx.Remove(c.lruRefs[itmID])
delete(c.lruRefs, itmID)
}
if c.ttl > 0 {
c.ttlIdx.Remove(c.ttlRefs[itmID])
delete(c.ttlRefs, itmID)
}
c.remItemFromGroups(ci.itemID, ci.groupIDs)
delete(c.cache, ci.itemID)
if c.onEvicted != nil {
c.onEvicted(ci.itemID, ci.value)
}
}
// cleanExpired checks items indexed for TTL and expires them when necessary
func (c *Cache) cleanExpired() {
for {
c.Lock()
if c.ttlIdx.Len() == 0 {
c.Unlock()
time.Sleep(c.ttl)
continue
}
ci := c.ttlIdx.Back().Value.(*cachedItem)
now := time.Now()
if now.Before(ci.expiryTime) {
remainingTTL := ci.expiryTime.Sub(now)
c.Unlock()
time.Sleep(remainingTTL)
continue
}
c.remove(ci.itemID)
c.Unlock()
}
}
// addItemToGroups adds and item to a group
func (c *Cache) addItemToGroups(itmKey string, groupIDs []string) {
for _, grpID := range groupIDs {
if _, has := c.groups[grpID]; !has {
c.groups[grpID] = make(map[string]struct{})
}
c.groups[grpID][itmKey] = struct{}{}
}
}
// remItemFromGroups removes an item with itemKey from groups
func (c *Cache) remItemFromGroups(itmKey string, groupIDs []string) {
for _, grpID := range groupIDs {
delete(c.groups[grpID], itmKey)
if len(c.groups[grpID]) == 0 {
delete(c.groups, grpID)
}
}
}
// Len returns the number of items in the cache.
func (c *Cache) Len() int {
c.RLock()
defer c.RUnlock()
return len(c.cache)
}
// Clear purges all stored items from the cache.
func (c *Cache) Clear() {
c.Lock()
defer c.Unlock()
if c.onEvicted != nil {
for _, ci := range c.cache {
c.onEvicted(ci.itemID, ci.value)
}
}
c.cache = make(map[string]*cachedItem)
c.groups = make(map[string]map[string]struct{})
c.lruIdx = c.lruIdx.Init()
c.lruRefs = make(map[string]*list.Element)
c.ttlIdx = c.ttlIdx.Init()
c.ttlRefs = make(map[string]*list.Element)
}
type CacheStats struct {
Items int
Groups int
}
// GetStats will return the CacheStats for this instance
func (c *Cache) GetCacheStats() (cs *CacheStats) {
c.RLock()
cs = &CacheStats{Items: len(c.cache), Groups: len(c.groups)}
c.RUnlock()
return
}