Add TrackingSet method

This method reduces the likelihood of a race condition where
you can add a (tracked) item to the cache, and the item isn't
the item you thought it was.

bucket.go

@@ -23,9 +23,9 @@ func (b *bucket) get(key string) *Item {
 	return b.lookup[key]
 }
 
-func (b *bucket) set(key string, value interface{}, duration time.Duration) (*Item, *Item) {
+func (b *bucket) set(key string, value interface{}, duration time.Duration, track bool) (*Item, *Item) {
 	expires := time.Now().Add(duration).UnixNano()
-	item := newItem(key, value, expires)
+	item := newItem(key, value, expires, track)
 	b.Lock()
 	existing := b.lookup[key]
 	b.lookup[key] = item

bucket_test.go

@@ -1,9 +1,10 @@
 package ccache
 
 import (
-	. "github.com/karlseguin/expect"
 	"testing"
 	"time"
+
+	. "github.com/karlseguin/expect"
 )
 
 type BucketTests struct {
@@ -32,7 +33,7 @@ func (_ *BucketTests) DeleteItemFromBucket() {
 
 func (_ *BucketTests) SetsANewBucketItem() {
 	bucket := testBucket()
-	item, existing := bucket.set("spice", TestValue("flow"), time.Minute)
+	item, existing := bucket.set("spice", TestValue("flow"), time.Minute, false)
 	assertValue(item, "flow")
 	item = bucket.get("spice")
 	assertValue(item, "flow")
@@ -41,7 +42,7 @@ func (_ *BucketTests) SetsANewBucketItem() {
 
 func (_ *BucketTests) SetsAnExistingItem() {
 	bucket := testBucket()
-	item, existing := bucket.set("power", TestValue("9001"), time.Minute)
+	item, existing := bucket.set("power", TestValue("9001"), time.Minute, false)
 	assertValue(item, "9001")
 	item = bucket.get("power")
 	assertValue(item, "9001")

cache.go

@@ -98,9 +98,15 @@ func (c *Cache) TrackingGet(key string) TrackedItem {
 	return item
 }
 
+// Used when the cache was created with the Track() configuration option.
+// Sets the item, and returns a tracked reference to it.
+func (c *Cache) TrackingSet(key string, value interface{}, duration time.Duration) TrackedItem {
+	return c.set(key, value, duration, true)
+}
+
 // Set the value in the cache for the specified duration
 func (c *Cache) Set(key string, value interface{}, duration time.Duration) {
-	c.set(key, value, duration)
+	c.set(key, value, duration, false)
 }
 
 // Replace the value if it exists, does not set if it doesn't.
@@ -127,7 +133,7 @@ func (c *Cache) Fetch(key string, duration time.Duration, fetch func() (interfac
 	if err != nil {
 		return nil, err
 	}
-	return c.set(key, value, duration), nil
+	return c.set(key, value, duration, false), nil
 }
 
 // Remove the item from the cache, return true if the item was present, false otherwise.
@@ -182,8 +188,8 @@ func (c *Cache) deleteItem(bucket *bucket, item *Item) {
 	c.deletables <- item
 }
 
-func (c *Cache) set(key string, value interface{}, duration time.Duration) *Item {
-	item, existing := c.bucket(key).set(key, value, duration)
+func (c *Cache) set(key string, value interface{}, duration time.Duration, track bool) *Item {
+	item, existing := c.bucket(key).set(key, value, duration, track)
 	if existing != nil {
 		c.deletables <- existing
 	}

cache_test.go

@@ -140,18 +140,21 @@ func (_ CacheTests) PromotedItemsDontGetPruned() {
 }
 
 func (_ CacheTests) TrackerDoesNotCleanupHeldInstance() {
-	cache := New(Configure().ItemsToPrune(10).Track())
-	for i := 0; i < 10; i++ {
+	cache := New(Configure().ItemsToPrune(11).Track())
+	item0 := cache.TrackingSet("0", 0, time.Minute)
+	for i := 1; i < 11; i++ {
 		cache.Set(strconv.Itoa(i), i, time.Minute)
 	}
-	item := cache.TrackingGet("0")
+	item1 := cache.TrackingGet("1")
 	time.Sleep(time.Millisecond * 10)
 	gcCache(cache)
 	Expect(cache.Get("0").Value()).To.Equal(0)
-	Expect(cache.Get("1")).To.Equal(nil)
-	item.Release()
+	Expect(cache.Get("1").Value()).To.Equal(1)
+	item0.Release()
+	item1.Release()
 	gcCache(cache)
 	Expect(cache.Get("0")).To.Equal(nil)
+	Expect(cache.Get("1")).To.Equal(nil)
 }
 
 func (_ CacheTests) RemovesOldestItemWhenFull() {

configuration_test.go

@@ -1,8 +1,9 @@
 package ccache
 
 import (
-	. "github.com/karlseguin/expect"
 	"testing"
+
+	. "github.com/karlseguin/expect"
 )
 
 type ConfigurationTests struct{}

item.go

@@ -52,18 +52,22 @@ type Item struct {
 	element    *list.Element
 }
 
-func newItem(key string, value interface{}, expires int64) *Item {
+func newItem(key string, value interface{}, expires int64, track bool) *Item {
 	size := int64(1)
 	if sized, ok := value.(Sized); ok {
 		size = sized.Size()
 	}
-	return &Item{
+	item := &Item{
 		key:        key,
 		value:      value,
 		promotions: 0,
 		size:       size,
 		expires:    expires,
 	}
+	if track {
+		item.refCount = 1
+	}
+	return item
 }
 
 func (i *Item) shouldPromote(getsPerPromote int32) bool {

layeredbucket.go

@@ -46,7 +46,7 @@ func (b *layeredBucket) set(primary, secondary string, value interface{}, durati
 		b.buckets[primary] = bkt
 	}
 	b.Unlock()
-	item, existing := bkt.set(secondary, value, duration)
+	item, existing := bkt.set(secondary, value, duration, false)
 	item.group = primary
 	return item, existing
 }

secondarycache.go

@@ -16,7 +16,7 @@ func (s *SecondaryCache) Get(secondary string) *Item {
 // Set the secondary key to a value.
 // The semantics are the same as for LayeredCache.Set
 func (s *SecondaryCache) Set(secondary string, value interface{}, duration time.Duration) *Item {
-	item, existing := s.bucket.set(secondary, value, duration)
+	item, existing := s.bucket.set(secondary, value, duration, false)
 	if existing != nil {
 		s.pCache.deletables <- existing
 	}

secondarycache_test.go

@@ -1,10 +1,11 @@
 package ccache
 
 import (
-	. "github.com/karlseguin/expect"
 	"strconv"
 	"testing"
 	"time"
+
+	. "github.com/karlseguin/expect"
 )
 
 type SecondaryCacheTests struct{}