Integrate feedback and upstream fixes

- Ensure correct locking in GetOrCreateSecondaryCache
- Fetch now returns a *Item

layeredcache.go

@@ -70,10 +70,12 @@ func (c *LayeredCache) Get(primary, secondary string) *Item {
 func (c *LayeredCache) GetOrCreateSecondaryCache(primary string) *SecondaryCache {
 	primaryBkt := c.bucket(primary)
 	bkt := primaryBkt.getSecondaryBucket(primary)
+	primaryBkt.Lock()
 	if bkt == nil {
 		bkt = &bucket{lookup: make(map[string]*Item)}
 		primaryBkt.buckets[primary] = bkt
 	}
+	primaryBkt.Unlock()
 	return &SecondaryCache{
 		bucket: bkt,
 		pCache: c,

secondarycache.go

@@ -26,7 +26,7 @@ func (s *SecondaryCache) Set(secondary string, value interface{}, duration time.
 
 // Fetch or set a secondary key.
 // The semantics are the same as for LayeredCache.Fetch
-func (s *SecondaryCache) Fetch(secondary string, duration time.Duration, fetch func() (interface{}, error)) (interface{}, error) {
+func (s *SecondaryCache) Fetch(secondary string, duration time.Duration, fetch func() (interface{}, error)) (*Item, error) {
 	item := s.Get(secondary)
 	if item != nil {
 		return item, nil

secondarycache_test.go

@@ -78,14 +78,14 @@ func (_ SecondaryCacheTests) FetchReturnsAnExistingValue() {
 	cache.Set("spice", "flow", "value-a", time.Minute)
 	sCache := cache.GetOrCreateSecondaryCache("spice")
 	val, _ := sCache.Fetch("flow", time.Minute, func() (interface{}, error) {return "a fetched value", nil})
-	Expect(val.(*Item).Value().(string)).To.Equal("value-a")
+	Expect(val.Value().(string)).To.Equal("value-a")
 }
 
 func (_ SecondaryCacheTests) FetchReturnsANewValue() {
 	cache := newLayered()
 	sCache := cache.GetOrCreateSecondaryCache("spice")
 	val, _ := sCache.Fetch("flow", time.Minute, func() (interface{}, error) {return "a fetched value", nil})
-	Expect(val.(*Item).Value().(string)).To.Equal("a fetched value")
+	Expect(val.Value().(string)).To.Equal("a fetched value")
 }
 
 func (_ SecondaryCacheTests) TrackerDoesNotCleanupHeldInstance() {