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

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

bucket.go

@@ -35,6 +35,22 @@ func (b *bucket[T]) get(key string) *Item[T] {
 	return b.lookup[key]
 }
 
+func (b *bucket[T]) setnx(key string, value T, duration time.Duration, track bool) *Item[T] {
+	b.Lock()
+	defer b.Unlock()
+
+	item := b.lookup[key]
+	if item != nil {
+		return item
+	}
+
+	expires := time.Now().Add(duration).UnixNano()
+	item = newItem(key, value, expires, track)
+	b.lookup[key] = item
+
+	return item
+}
+
 func (b *bucket[T]) set(key string, value T, duration time.Duration, track bool) (*Item[T], *Item[T]) {
 	expires := time.Now().Add(duration).UnixNano()
 	item := newItem(key, value, expires, track)

cache.go

@@ -146,6 +146,11 @@ func (c *Cache[T]) Set(key string, value T, duration time.Duration) {
 	c.set(key, value, duration, false)
 }
 
+// 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)
+}
+
 // Replace the value if it exists, does not set if it doesn't.
 // Returns true if the item existed an was replaced, false otherwise.
 // Replace does not reset item's TTL
@@ -200,6 +205,10 @@ 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))

cache_test.go

@@ -12,6 +12,27 @@ import (
 	"github.com/karlseguin/ccache/v3/assert"
 )
 
+func Test_Setnx(t *testing.T) {
+	cache := New(Configure[string]())
+	defer cache.Stop()
+	assert.Equal(t, cache.ItemCount(), 0)
+
+	cache.Set("spice", "flow", time.Minute)
+	assert.Equal(t, cache.ItemCount(), 1)
+
+	// set if exists
+	cache.Setnx("spice", "worm", time.Minute)
+	assert.Equal(t, cache.ItemCount(), 1)
+	assert.Equal(t, cache.Get("spice").Value(), "flow")
+
+	// set if not exists
+	cache.Delete("spice")
+	cache.Setnx("spice", "worm", time.Minute)
+	assert.Equal(t, cache.Get("spice").Value(), "worm")
+
+	assert.Equal(t, cache.ItemCount(), 1)
+}
+
 func Test_CacheDeletesAValue(t *testing.T) {
 	cache := New(Configure[string]())
 	defer cache.Stop()

readme.md

@@ -122,6 +122,14 @@ cache.Replace("user:4", user)
 
 `Replace` returns true if the item existed (and thus was replaced). In the case where the key was not in the cache, the value *is not* inserted and false is returned.
 
+### Setnx
+
+Set the value if not exists. setnx will first check whether kv exists. If it does not exist, set kv in cache. this operation is atomic.
+
+```go
+cache.Set("user:4", user, time.Minute * 10)
+```
+
 ### GetDropped
 You can get the number of keys evicted due to memory pressure by calling `GetDropped`: