Make GetOrCreate return a bool indicating if the value was found in the cache

Author: bep

lazycache.go

@@ -83,19 +83,20 @@ func (c *Cache[K, V]) Get(key K) (V, bool) {
 }
 
 // GetOrCreate returns the value associated with key, or creates it if it doesn't.
+// It also returns a bool indicating if the value was found in the cache.
 // Note that create, the cache prime function, is called once and then not called again for a given key
 // unless the cache entry is evicted; it does not block other goroutines from calling GetOrCreate,
 // it is not called with the cache lock held.
 // Note that any error returned by create will be returned by GetOrCreate and repeated calls with the same key will
 // receive the same error.
-func (c *Cache[K, V]) GetOrCreate(key K, create func(key K) (V, error)) (V, error) {
+func (c *Cache[K, V]) GetOrCreate(key K, create func(key K) (V, error)) (V, bool, error) {
 	c.mu.Lock()
 	w := c.get(key)
 	if w != nil {
 		c.mu.Unlock()
 		w.wait()
 		// If w.ready is nil, we will repeat any error from the create function to concurrent callers.
-		return w.value, w.err
+		return w.value, true, w.err
 	}
 
 	w = &valueWrapper[V]{
@@ -117,9 +118,9 @@ func (c *Cache[K, V]) GetOrCreate(key K, create func(key K) (V, error)) (V, erro
 
 	if err != nil {
 		c.Delete(key)
-		return c.zerov, err
+		return c.zerov, false, err
 	}
-	return v, nil
+	return v, false, nil
 }
 
 // Resize changes the cache size and returns the number of entries evicted.

lazycache_test.go

@@ -87,7 +87,7 @@ func TestDeleteFunc(t *testing.T) {
 			go func() {
 				defer wg.Done()
 				for i := 10; i < 30; i++ {
-					v, err := cache.GetOrCreate(i, func(key int) (any, error) {
+					v, _, err := cache.GetOrCreate(i, func(key int) (any, error) {
 						if key%2 == 0 {
 							return nil, errors.New("failed")
 						}
@@ -124,9 +124,10 @@ func TestGetOrCreate(t *testing.T) {
 		return fmt.Sprintf("value-%d-%d", key, counter), nil
 	}
 	for i := 0; i < 3; i++ {
-		res, err := cache.GetOrCreate(123456, create)
+		res, found, err := cache.GetOrCreate(123456, create)
 		c.Assert(err, qt.IsNil)
 		c.Assert(res, qt.Equals, "value-123456-1")
+		c.Assert(found, qt.Equals, i > 0)
 	}
 	v, found := cache.Get(123456)
 	c.Assert(found, qt.IsTrue)
@@ -140,7 +141,7 @@ func TestGetOrCreateError(t *testing.T) {
 		return nil, fmt.Errorf("failed")
 	}
 
-	res, err := cache.GetOrCreate(123456, create)
+	res, _, err := cache.GetOrCreate(123456, create)
 	c.Assert(err, qt.ErrorMatches, "failed")
 	c.Assert(res, qt.IsNil)
 
@@ -171,7 +172,7 @@ func TestGetOrCreateConcurrent(t *testing.T) {
 		go func() {
 			defer wg.Done()
 			for j := 0; j < 12; j++ {
-				res, err := cache.GetOrCreate(i, create)
+				res, _, err := cache.GetOrCreate(i, create)
 				c.Assert(err, qt.IsNil)
 				c.Assert(res, qt.Equals, expect)
 			}
@@ -221,11 +222,11 @@ func TestGetOrCreateRecursive(t *testing.T) {
 						key2++
 					}
 					shouldFail := key1%10 == 0
-					v, err := cache.GetOrCreate(key1, func(key int) (any, error) {
+					v, _, err := cache.GetOrCreate(key1, func(key int) (any, error) {
 						if shouldFail {
 							return nil, fmt.Errorf("failed")
 						}
-						v, err := cache.GetOrCreate(key2, func(key int) (any, error) {
+						v, _, err := cache.GetOrCreate(key2, func(key int) (any, error) {
 							return "inner", nil
 						})
 						c.Assert(err, qt.IsNil)
@@ -272,7 +273,7 @@ func BenchmarkGetOrCreateAndGet(b *testing.B) {
 				b.Fatalf("got %v, want %v", v, i1)
 			}
 
-			res2, err := cache.GetOrCreate(i2, func(key int) (any, error) {
+			res2, _, err := cache.GetOrCreate(i2, func(key int) (any, error) {
 				if i2%100 == 0 {
 					// Simulate a slow create.
 					time.Sleep(1 * time.Second)
@@ -312,7 +313,7 @@ func BenchmarkGetOrCreate(b *testing.B) {
 			key := r.Intn(maxSize)
 			mu.Unlock()
 
-			v, err := cache.GetOrCreate(key, func(int) (any, error) {
+			v, _, err := cache.GetOrCreate(key, func(int) (any, error) {
 				if key%100 == 0 {
 					// Simulate a slow create.
 					time.Sleep(1 * time.Second)