use integer counter for promotions instead of time

bucket.go

@@ -24,7 +24,7 @@ func (b *Bucket) set(key string, value Value) *Item {
     existing.Unlock()
     return existing
   }
-  item := &Item{key: key, value: value}
+  item := newItem(key, value)
   b.lookup[key] = item
   return item
 }

cache.go

@@ -56,7 +56,7 @@ func (c *Cache) bucket(key string) *Bucket {
 }
 
 func (c *Cache) promote(item *Item) {
-  if item.shouldPromote(c.promoteDelay) == false { return }
+  if item.shouldPromote() == false { return }
   c.promotables <- item
 }
 
@@ -75,7 +75,7 @@ func (c *Cache) worker() {
 func (c *Cache) doPromote(item *Item) bool {
   item.Lock()
   defer item.Unlock()
-  item.promoted = time.Now()
+  item.promotions = 0
   if item.element != nil { //not a new item
     c.list.MoveToFront(item.element)
     return false

configuration.go

@@ -1,15 +1,10 @@
 package ccache
 
-import (
-  "time"
-)
-
 type Configuration struct {
   size uint64
   buckets int
   itemsToPrune int
   promoteBuffer int
-  promoteDelay time.Duration
 }
 
 func Configure() *Configuration {
@@ -18,7 +13,6 @@ func Configure() *Configuration {
     itemsToPrune: 500,
     promoteBuffer: 1024,
     size: 500 * 1024 * 1024,
-    promoteDelay: time.Minute * -5,
   }
 }
 
@@ -41,8 +35,3 @@ func (c *Configuration) PromoteBuffer(size int) *Configuration {
   c.promoteBuffer = size
   return c
 }
-
-func (c *Configuration) PromoteDelay(delay time.Duration) *Configuration {
-  c.promoteDelay = -delay
-  return c
-}

item.go

@@ -2,21 +2,32 @@ package ccache
 
 import (
   "sync"
-  "time"
+  "sync/atomic"
   "container/list"
 )
 
+const promoteCap = 5
+
 type Item struct {
   key string
   value Value
   sync.RWMutex
-  promoted time.Time
+  promotions int32
   element *list.Element
 }
 
-func (i *Item) shouldPromote(staleness time.Duration) bool {
-  stale := time.Now().Add(staleness)
-  i.RLock()
-  defer i.RUnlock()
-  return i.promoted.Before(stale)
+func newItem(key string, value Value) *Item {
+  return &Item{
+    key: key,
+    value: value,
+    promotions: -1,
+  }
+}
+
+func (i *Item) shouldPromote() bool {
+  promotions := atomic.AddInt32(&i.promotions, 1)
+  if promotions == promoteCap || promotions == 0 {
+    return true
+  }
+  return false
 }

item_test.go

@@ -1,14 +1,17 @@
 package ccache
 
 import (
-  "time"
   "testing"
   "github.com/karlseguin/gspec"
 )
 
 func TestItemPromotability(t *testing.T) {
   spec := gspec.New(t)
-  item := &Item{promoted: time.Now().Add(time.Second * -5)}
-  spec.Expect(item.shouldPromote(time.Second * -2)).ToEqual(true)
-  spec.Expect(item.shouldPromote(time.Second * -6)).ToEqual(false)
+  item := &Item{promotions: -1}
+  spec.Expect(item.shouldPromote()).ToEqual(true)
+  spec.Expect(item.shouldPromote()).ToEqual(false)
+
+  item.promotions = 4
+  spec.Expect(item.shouldPromote()).ToEqual(true)
+  spec.Expect(item.shouldPromote()).ToEqual(false)
 }