add silding get to cache

cache.go

@@ -49,6 +49,12 @@ func (c *Cache[K, V]) Get(key K) (value V, ok bool) {
 	return c.shards[hash&c.mask].Get(hash, key)
 }
 
+// SlidingGet returns value for key and reset the expires with TTL(aka, Sliding Cache).
+func (c *Cache[K, V]) SlidingGet(key K) (value V, ok bool) {
+	hash := uint32(c.hasher.Hash(key))
+	return c.shards[hash&c.mask].SlidingGet(hash, key)
+}
+
 // Peek returns value for key, but does not modify its recency.
 func (c *Cache[K, V]) Peek(key K) (value V, ok bool) {
 	hash := uint32(c.hasher.Hash(key))

cache_test.go

@@ -92,6 +92,22 @@ func TestCacheEviction(t *testing.T) {
 	}
 }
 
+func TestCacheSlidingGet(t *testing.T) {
+	l := newWithShards[string, int](1, 256)
+
+	l.SetWithTTL("foobar", 42, 400*time.Millisecond)
+
+	time.Sleep(200 * time.Millisecond)
+	if v, ok := l.SlidingGet("foobar"); !ok || v != 42 {
+		t.Errorf("foobar should be set to 42: %v,", v)
+	}
+
+	time.Sleep(300 * time.Millisecond)
+	if v, ok := l.Get("foobar"); !ok || v != 42 {
+		t.Errorf("foobar should be still set to 42: %v,", v)
+	}
+}
+
 func TestCachePeek(t *testing.T) {
 	l := New[int, int](64)
 

list.go

@@ -6,6 +6,7 @@ type node[K comparable, V any] struct {
 	key     K
 	value   V
 	expires int64
+	ttl     int64
 	next    uint32
 	prev    uint32
 }

shard.go

@@ -38,6 +38,31 @@ func (s *shard[K, V]) Get(hash uint32, key K) (value V, ok bool) {
 	return
 }
 
+func (s *shard[K, V]) SlidingGet(hash uint32, key K) (value V, ok bool) {
+	s.mu.Lock()
+
+	if index, exists := s.table.Get(hash, key); exists {
+		if expires := s.list.nodes[index].expires; expires == 0 {
+			s.list.MoveToFront(index)
+			value = s.list.nodes[index].value
+			ok = true
+		} else if now := atomic.LoadInt64(&clock); now < expires {
+			s.list.MoveToFront(index)
+			s.list.nodes[index].expires = atomic.LoadInt64(&clock) + s.list.nodes[index].ttl
+			value = s.list.nodes[index].value
+			ok = true
+		} else {
+			s.list.MoveToBack(index)
+			s.list.nodes[index].value = value
+			s.table.Delete(hash, key)
+		}
+	}
+
+	s.mu.Unlock()
+
+	return
+}
+
 func (s *shard[K, V]) Peek(hash uint32, key K) (value V, ok bool) {
 	s.mu.Lock()
 
@@ -61,6 +86,7 @@ func (s *shard[K, V]) Set(hash uint32, hashfun func(K) uint64, key K, value V, t
 		s.list.MoveToFront(index)
 		node.value = value
 		if ttl > 0 {
+			node.ttl = int64(ttl)
 			node.expires = atomic.LoadInt64(&clock) + int64(ttl)
 		}
 		prev = previousValue
@@ -76,6 +102,7 @@ func (s *shard[K, V]) Set(hash uint32, hashfun func(K) uint64, key K, value V, t
 	node.key = key
 	node.value = value
 	if ttl > 0 {
+		node.ttl = int64(ttl)
 		node.expires = atomic.LoadInt64(&clock) + int64(ttl)
 	}
 	s.table.Set(hash, key, index)