Don't use defer for mutex unlocking (it currently adds ~200ns)

cache.go

@@ -34,6 +34,8 @@ type Cache struct {
 type cache struct {
 	DefaultExpiration time.Duration
 	Items             map[string]*Item
+	// TODO: Calls to mu.Unlock are currently not deferred because defer
+	// adds ~200 ns (as of 792c7561af4b+ tip.)
 	mu                sync.Mutex
 	janitor           *janitor
 }
@@ -42,9 +44,8 @@ type cache struct {
 // cache's default expiration time is used. If it is -1, the item never expires.
 func (c *cache) Set(k string, x interface{}, d time.Duration) {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	c.set(k, x, d)
+	c.mu.Unlock()
 }
 
 func (c *cache) set(k string, x interface{}, d time.Duration) {
@@ -66,13 +67,13 @@ func (c *cache) set(k string, x interface{}, d time.Duration) {
 // or if the existing item has expired. Returns an error if not.
 func (c *cache) Add(k string, x interface{}, d time.Duration) error {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	_, found := c.get(k)
 	if found {
+		c.mu.Unlock()
 		return fmt.Errorf("Item %s already exists", k)
 	}
 	c.set(k, x, d)
+	c.mu.Unlock()
 	return nil
 }
 
@@ -80,13 +81,13 @@ func (c *cache) Add(k string, x interface{}, d time.Duration) error {
 // it does not.
 func (c *cache) Replace(k string, x interface{}, d time.Duration) error {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	_, found := c.get(k)
 	if !found {
+		c.mu.Unlock()
 		return fmt.Errorf("Item %s doesn't exist", k)
 	}
 	c.set(k, x, d)
+	c.mu.Unlock()
 	return nil
 }
 
@@ -94,9 +95,9 @@ func (c *cache) Replace(k string, x interface{}, d time.Duration) error {
 // the given key was found in the cache.
 func (c *cache) Get(k string) (interface{}, bool) {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
-	return c.get(k)
+	x, found := c.get(k)
+	c.mu.Unlock()
+	return x, found
 }
 
 func (c *cache) get(k string) (interface{}, bool) {
@@ -117,16 +118,16 @@ func (c *cache) get(k string) (interface{}, bool) {
 // n. Passing a negative number will cause the item to be decremented.
 func (c *cache) IncrementFloat(k string, n float64) error {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	v, found := c.Items[k]
 	if !found || v.Expired() {
+		c.mu.Unlock()
 		return fmt.Errorf("Item not found")
 	}
 
 	t := reflect.TypeOf(v.Object)
 	switch t.Kind() {
 	default:
+		c.mu.Unlock()
 		return fmt.Errorf("The value of %s is not an integer", k)
 	case reflect.Uint:
 		v.Object = v.Object.(uint) + uint(n)
@@ -155,6 +156,7 @@ func (c *cache) IncrementFloat(k string, n float64) error {
 	case reflect.Float64:
 		v.Object = v.Object.(float64) + n
 	}
+	c.mu.Unlock()
 	return nil
 }
 
@@ -177,9 +179,8 @@ func (c *cache) Decrement(k string, n int64) error {
 // Deletes an item from the cache. Does nothing if the item does not exist in the cache.
 func (c *cache) Delete(k string) {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	c.delete(k)
+	c.mu.Unlock()
 }
 
 func (c *cache) delete(k string) {
@@ -189,13 +190,12 @@ func (c *cache) delete(k string) {
 // Deletes all expired items from the cache.
 func (c *cache) DeleteExpired() {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	for k, v := range c.Items {
 		if v.Expired() {
 			c.delete(k)
 		}
 	}
+	c.mu.Unlock()
 }
 
 // Writes the cache's items (using Gob) to an io.Writer.
@@ -262,9 +262,8 @@ func (c *cache) LoadFile(fname string) error {
 // Deletes all items from the cache.
 func (c *cache) Flush() {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	c.Items = map[string]*Item{}
+	c.mu.Unlock()
 }
 
 type janitor struct {

cache_test.go

@@ -675,11 +675,11 @@ func BenchmarkCacheSetDelete(b *testing.B) {
 func BenchmarkCacheSetDeleteSingleLock(b *testing.B) {
 	tc := New(0, 0)
 	tc.mu.Lock()
-	defer tc.mu.Unlock()
 	for i := 0; i < b.N; i++ {
 		tc.set("foo", "bar", 0)
 		tc.delete("foo")
 	}
+	tc.mu.Unlock()
 }
 
 func BenchmarkMapSetDelete(b *testing.B) {