snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

internal/wrr/random.go

@@ -0,0 +1,84 @@
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package wrr
+
+import (
+	"fmt"
+	rand "math/rand/v2"
+	"sort"
+)
+
+// weightedItem is a wrapped weighted item that is used to implement weighted random algorithm.
+type weightedItem struct {
+	item              any
+	weight            int64
+	accumulatedWeight int64
+}
+
+func (w *weightedItem) String() string {
+	return fmt.Sprint(*w)
+}
+
+// randomWRR is a struct that contains weighted items implement weighted random algorithm.
+type randomWRR struct {
+	items []*weightedItem
+	// Are all item's weights equal
+	equalWeights bool
+}
+
+// NewRandom creates a new WRR with random.
+func NewRandom() WRR {
+	return &randomWRR{}
+}
+
+var randInt64n = rand.Int64N
+
+func (rw *randomWRR) Next() (item any) {
+	if len(rw.items) == 0 {
+		return nil
+	}
+	if rw.equalWeights {
+		return rw.items[randInt64n(int64(len(rw.items)))].item
+	}
+
+	sumOfWeights := rw.items[len(rw.items)-1].accumulatedWeight
+	// Random number in [0, sumOfWeights).
+	randomWeight := randInt64n(sumOfWeights)
+	// Item's accumulated weights are in ascending order, because item's weight >= 0.
+	// Binary search rw.items to find first item whose accumulatedWeight > randomWeight
+	// The return i is guaranteed to be in range [0, len(rw.items)) because randomWeight < last item's accumulatedWeight
+	i := sort.Search(len(rw.items), func(i int) bool { return rw.items[i].accumulatedWeight > randomWeight })
+	return rw.items[i].item
+}
+
+func (rw *randomWRR) Add(item any, weight int64) {
+	accumulatedWeight := weight
+	equalWeights := true
+	if len(rw.items) > 0 {
+		lastItem := rw.items[len(rw.items)-1]
+		accumulatedWeight = lastItem.accumulatedWeight + weight
+		equalWeights = rw.equalWeights && weight == lastItem.weight
+	}
+	rw.equalWeights = equalWeights
+	rItem := &weightedItem{item: item, weight: weight, accumulatedWeight: accumulatedWeight}
+	rw.items = append(rw.items, rItem)
+}
+
+func (rw *randomWRR) String() string {
+	return fmt.Sprint(rw.items)
+}