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cache.go
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cache.go
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package store
import (
"sync"
"time"
du "panorama/util"
)
type CacheItem struct {
expires time.Time
Value interface{}
}
type CacheBase struct {
sync.RWMutex
ttl time.Duration
}
type Cache struct {
CacheBase
items map[string]*CacheItem
}
type CacheListItem struct {
chain []*CacheItem
}
type CacheList struct {
CacheBase
items map[string]*CacheListItem
max_list_len int
}
const (
RETIRE_LIST_LEN = 100
EXPIRE_WRITE_LEN = 50
ctag = "cache"
)
var (
retired = make([]string, RETIRE_LIST_LEN)
)
func NewCacheList(ttl time.Duration, max_list_len int) *CacheList {
return &CacheList{
CacheBase: CacheBase{ttl: ttl},
items: make(map[string]*CacheListItem),
max_list_len: max_list_len,
}
}
func NewCache(ttl time.Duration) *Cache {
c := &Cache{
CacheBase: CacheBase{ttl: ttl},
items: make(map[string]*CacheItem),
}
return c
}
func (i *CacheItem) Expired() bool {
d := time.Now().Sub(i.expires)
return d >= 0
}
func (i *CacheItem) TTL() time.Duration {
return time.Now().Sub(i.expires)
}
func (c *Cache) Get(key string) interface{} {
c.RLock()
item, ok := c.items[key]
c.RUnlock()
if !ok {
return nil
}
if item.Expired() {
c.Lock()
delete(c.items, key) // delete expired cache item from cache
c.Unlock()
du.LogD(ctag, "Entry for %s has expired (added at %s)", key, item.expires.Add(-1*c.ttl))
return nil
}
return item.Value
}
func (c *Cache) Set(key string, value interface{}) {
item := &CacheItem{
expires: time.Now().Add(c.ttl),
Value: value,
}
c.Lock()
c.items[key] = item
c.Unlock()
if len(c.items) >= EXPIRE_WRITE_LEN {
go c.reap() // trigger reaping when there are too many entries
}
}
func (c *Cache) Delete(key string) {
c.Lock()
delete(c.items, key)
c.Unlock()
}
func (c *Cache) Clear() {
c.Lock()
c.items = make(map[string]*CacheItem)
c.Unlock()
}
func (c *Cache) reap() {
c.RLock()
i := 0
for key, item := range c.items {
if item.Expired() {
if i >= RETIRE_LIST_LEN {
break
}
retired[i] = key
i++
}
}
c.Unlock()
if i == 0 { // no item has expired yet
return
}
c.Lock()
for j := 0; j < i; j++ {
delete(c.items, retired[j])
}
c.Unlock()
}
func (c *CacheList) Process(key string, fn func(*CacheItem) bool) int {
c.Lock()
defer c.Unlock()
litem, ok := c.items[key]
if !ok {
return 0
}
var i, j, processed int
var item *CacheItem
newchain := make([]*CacheItem, 0, c.max_list_len+1)
j = 0
processed = 0
for i = 0; i < len(litem.chain); i++ {
item = litem.chain[i]
if !item.Expired() {
continue
}
processed++
if !fn(item) {
// only retain them if the processing function says so
newchain[j] = item
j++
}
}
du.LogD(ctag, "%d entries remaining after expiring and processing the list", j)
litem.chain = newchain
return processed
}
func (c *CacheList) Get(key string) []*CacheItem {
c.Lock()
defer c.Unlock()
litem, ok := c.items[key]
if !ok {
return nil
}
var i int
var item *CacheItem
// the items in the chain are in chronological order
// so once we find an unexpired item, we are done
for i = 0; i < len(litem.chain); i++ {
item = litem.chain[i]
if !item.Expired() {
break
}
}
if i > 0 {
du.LogD(ctag, "%d/%d entires for %s has been expired", i, len(litem.chain), key)
litem.chain = litem.chain[i:] // discard the expired items
}
return litem.chain
}
func (c *CacheList) Set(key string, value interface{}) {
item := &CacheItem{
expires: time.Now().Add(c.ttl),
Value: value,
}
c.Lock()
litem, ok := c.items[key]
if !ok {
lst := make([]*CacheItem, 0, c.max_list_len+1)
litem = &CacheListItem{lst}
c.items[key] = litem
}
litem.chain = append(litem.chain, item)
if len(litem.chain) > c.max_list_len {
litem.chain = litem.chain[1:]
du.LogD(ctag, "truncating cache list for %s to make room for %v", key, value)
}
c.Unlock()
}
func (c *CacheList) Delete(key string) {
c.Lock()
delete(c.items, key)
c.Unlock()
}
func (c *CacheList) Empty(key string) {
c.Lock()
litem, ok := c.items[key]
if ok {
litem.chain = make([]*CacheItem, 0, c.max_list_len+1)
}
c.Unlock()
}