feat: add setnx (if not exists, set kv)

Signed-off-by: rfyiamcool <rfyiamcool@163.com>

Author: rfyiamcool

bucket.go

@@ -36,19 +36,27 @@ func (b *bucket[T]) get(key string) *Item[T] {
 }
 
 func (b *bucket[T]) setnx(key string, value T, duration time.Duration, track bool) *Item[T] {
-	b.Lock()
-	defer b.Unlock()
-
+	b.RLock()
 	item := b.lookup[key]
+	b.RUnlock()
 	if item != nil {
 		return item
 	}
 
 	expires := time.Now().Add(duration).UnixNano()
-	item = newItem(key, value, expires, track)
-	b.lookup[key] = item
+	newItem := newItem(key, value, expires, track)
 
-	return item
+	b.Lock()
+	defer b.Unlock()
+
+	// check again under write lock
+	item = b.lookup[key]
+	if item != nil {
+		return item
+	}
+
+	b.lookup[key] = newItem
+	return newItem
 }
 
 func (b *bucket[T]) set(key string, value T, duration time.Duration, track bool) (*Item[T], *Item[T]) {

cache.go

@@ -148,7 +148,7 @@ func (c *Cache[T]) Set(key string, value T, duration time.Duration) {
 
 // Setnx set the value in the cache for the specified duration if not exists
 func (c *Cache[T]) Setnx(key string, value T, duration time.Duration) {
-	c.setnx(key, value, duration, false)
+	c.bucket(key).setnx(key, value, duration, false)
 }
 
 // Replace the value if it exists, does not set if it doesn't.
@@ -205,10 +205,6 @@ func (c *Cache[T]) set(key string, value T, duration time.Duration, track bool)
 	return item
 }
 
-func (c *Cache[T]) setnx(key string, value T, duration time.Duration, track bool) *Item[T] {
-	return c.bucket(key).setnx(key, value, duration, track)
-}
-
 func (c *Cache[T]) bucket(key string) *bucket[T] {
 	h := fnv.New32a()
 	h.Write([]byte(key))