Add Cache.Has method

fastcache.go

@@ -154,7 +154,16 @@ func (c *Cache) Set(k, v []byte) {
 func (c *Cache) Get(dst, k []byte) []byte {
 	h := xxhash.Sum64(k)
 	idx := h % bucketsCount
-	return c.buckets[idx].Get(dst, k, h)
+	dst, _ = c.buckets[idx].Get(dst, k, h, true)
+	return dst
+}
+
+// Has returns true if entry for the given key k exists in the cache.
+func (c *Cache) Has(k []byte) bool {
+	h := xxhash.Sum64(k)
+	idx := h % bucketsCount
+	_, ok := c.buckets[idx].Get(nil, k, h, false)
+	return ok
 }
 
 // Del deletes value for the given k from the cache.
@@ -332,7 +341,7 @@ func (b *bucket) Set(k, v []byte, h uint64) {
 	b.mu.Unlock()
 }
 
-func (b *bucket) Get(dst, k []byte, h uint64) []byte {
+func (b *bucket) Get(dst, k []byte, h uint64, returnDst bool) ([]byte, bool) {
 	atomic.AddUint64(&b.getCalls, 1)
 	found := false
 	b.mu.RLock()
@@ -365,7 +374,9 @@ func (b *bucket) Get(dst, k []byte, h uint64) []byte {
 			}
 			if string(k) == string(chunk[idx:idx+keyLen]) {
 				idx += keyLen
-				dst = append(dst, chunk[idx:idx+valLen]...)
+				if returnDst {
+					dst = append(dst, chunk[idx:idx+valLen]...)
+				}
 				found = true
 			} else {
 				atomic.AddUint64(&b.collisions, 1)
@@ -377,7 +388,7 @@ end:
 	if !found {
 		atomic.AddUint64(&b.misses, 1)
 	}
-	return dst
+	return dst, found
 }
 
 func (b *bucket) Del(h uint64) {

fastcache_test.go

@@ -43,6 +43,20 @@ func TestCacheSmall(t *testing.T) {
 	if len(v) != 0 {
 		t.Fatalf("unexpected non-empty value obtained from empty cache: %q", v)
 	}
+
+	// Test empty value
+	k := []byte("empty")
+	c.Set(k, nil)
+	v = c.Get(nil, k)
+	if len(v) != 0 {
+		t.Fatalf("unexpected non-empty value obtained from empty entry: %q", v)
+	}
+	if !c.Has(k) {
+		t.Fatalf("cannot find empty entry for key %q", k)
+	}
+	if c.Has([]byte("foobar")) {
+		t.Fatalf("non-existing entry found in the cache")
+	}
 }
 
 func TestCacheWrap(t *testing.T) {

fastcache_timing_test.go

@@ -181,6 +181,37 @@ func BenchmarkCacheGet(b *testing.B) {
 	})
 }
 
+func BenchmarkCacheHas(b *testing.B) {
+	const items = 1 << 16
+	c := New(12 * items)
+	defer c.Reset()
+	k := []byte("\x00\x00\x00\x00")
+	for i := 0; i < items; i++ {
+		k[0]++
+		if k[0] == 0 {
+			k[1]++
+		}
+		c.Set(k, nil)
+	}
+
+	b.ReportAllocs()
+	b.SetBytes(items)
+	b.RunParallel(func(pb *testing.PB) {
+		k := []byte("\x00\x00\x00\x00")
+		for pb.Next() {
+			for i := 0; i < items; i++ {
+				k[0]++
+				if k[0] == 0 {
+					k[1]++
+				}
+				if !c.Has(k) {
+					panic(fmt.Errorf("BUG: missing value for key %q", k))
+				}
+			}
+		}
+	})
+}
+
 func BenchmarkCacheSetGet(b *testing.B) {
 	const items = 1 << 16
 	c := New(12 * items)