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cache.go
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cache.go
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//http://openmymind.net/Shard-Your-Hash-table-to-reduce-write-locks/
package atm
import (
"crypto/sha1"
"fmt"
"runtime"
"sync"
"time"
)
type Cache map[string]*shard
type shard struct {
items map[string]interface{}
lock *sync.RWMutex
}
type expiringItem struct {
Object interface{}
Expiration *time.Time
}
func (i *expiringItem) Expired() bool {
if nil == i.Expiration {
return false
}
return i.Expiration.Before(time.Now().UTC())
}
type ExpiringCache struct {
*exCache
}
type exCache struct {
*Cache
scrubber *scrubber
}
type scrubber struct {
Interval time.Duration
stop chan bool
}
func (s *scrubber) Run(c *exCache) {
s.stop = make(chan bool)
ticker := time.NewTimer(s.Interval)
for {
select {
case <-ticker.C:
c.DeleteExpired()
case <-s.stop:
ticker.Stop()
return
}
}
}
func startSrubber(e *exCache, d time.Duration) {
s := &scrubber{
Interval: d,
}
e.scrubber = s
go s.Run(e)
}
func stopScrubber(c *ExpiringCache) {
c.scrubber.stop <- true
}
func NewExpiringCache(scrubInterval time.Duration) *ExpiringCache {
ex := &exCache{
Cache: NewCache(),
}
E := &ExpiringCache{ex}
startSrubber(ex, scrubInterval)
runtime.SetFinalizer(E, stopScrubber)
return E
}
func (c *ExpiringCache) Set(k string, v interface{}, d time.Duration) {
t := time.Now().UTC().Add(d)
o := &expiringItem{
Object: v,
Expiration: &t,
}
c.Cache.Set(k, o)
}
func (c *ExpiringCache) Get(k string) (interface{}, bool) {
i, f := c.Cache.Get(k)
if !f {
return nil, f
}
o := i.(*expiringItem)
if o.Expired() {
return nil, false
}
return o.Object, true
}
func NewCache() *Cache {
c := make(Cache, 256)
for i := 0; i < 256; i++ {
c[fmt.Sprintf("%02x", i)] = &shard{
items: make(map[string]interface{}, 2048),
lock: new(sync.RWMutex),
}
}
return &c
}
func (c *exCache) DeleteExpired() {
for _, shard := range *c.Cache {
shard.lock.Lock()
for k, v := range shard.items {
i := v.(*expiringItem)
if i.Expired() {
delete(shard.items, k)
}
}
shard.lock.Unlock()
}
}
func (c *Cache) Get(key string) (interface{}, bool) {
shard := c.getShard(key)
shard.lock.RLock()
i, r := shard.items[key]
shard.lock.RUnlock()
return i, r
}
func (c *Cache) Set(key string, data interface{}) {
shard := c.getShard(key)
shard.lock.Lock()
shard.items[key] = data
shard.lock.Unlock()
}
func (c *Cache) Delete(key string) {
shard := c.getShard(key)
shard.lock.Lock()
delete(shard.items, key)
shard.lock.Unlock()
}
func (c *Cache) getShard(key string) (shard *shard) {
hasher := sha1.New()
hasher.Write([]byte(key))
shardKey := fmt.Sprintf("%x", hasher.Sum(nil))[0:2]
return (*c)[shardKey]
}