[GitHub] [dubbo-go] AlexStocks commented on a diff in pull request #1828: xds ring hash

[GitBox <gi...@apache.org>]

AlexStocks commented on code in PR #1828:
URL: https://github.com/apache/dubbo-go/pull/1828#discussion_r847977767


##########
cluster/loadbalance/xds/ringhash/ring.go:
##########
@@ -0,0 +1,170 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 ringhash
+
+import (
+	"fmt"
+	"math"
+	"math/bits"
+	"sort"
+	"strconv"
+)
+
+import (
+	"github.com/cespare/xxhash/v2"
+)
+
+import (
+	"dubbo.apache.org/dubbo-go/v3/protocol"
+	"dubbo.apache.org/dubbo-go/v3/xds/client/resource"
+	"dubbo.apache.org/dubbo-go/v3/xds/utils/grpcrand"
+)
+
+type invokerWithWeight struct {
+	invoker protocol.Invoker
+	weight  float64
+}
+
+type ringEntry struct {
+	idx     int
+	hash    uint64
+	invoker protocol.Invoker
+}
+
+func (lb *ringhashLoadBalance) generateRing(invokers []invokerWrapper, minRingSize, maxRingSize uint64) ([]*ringEntry, error) {
+	normalizedWeights, minWeight, err := normalizeWeights(invokers)
+	if err != nil {
+		return nil, err
+	}
+	// Normalized weights for {3,3,4} is {0.3,0.3,0.4}.
+
+	// Scale up the size of the ring such that the least-weighted host gets a
+	// whole number of hashes on the ring.
+	//
+	// Note that size is limited by the input max/min.
+	scale := math.Min(math.Ceil(minWeight*float64(minRingSize))/minWeight, float64(maxRingSize))
+	ringSize := math.Ceil(scale)
+	items := make([]*ringEntry, 0, int(ringSize))
+
+	// For each entry, scale*weight nodes are generated in the ring.
+	//
+	// Not all of these are whole numbers. E.g. for weights {a:3,b:3,c:4}, if
+	// ring size is 7, scale is 6.66. The numbers of nodes will be
+	// {a,a,b,b,c,c,c}.
+	//
+	// A hash is generated for each item, and later the results will be sorted
+	// based on the hash.
+	var (
+		idx       int
+		targetIdx float64
+	)
+	for _, inw := range normalizedWeights {
+		targetIdx += scale * inw.weight
+		for float64(idx) < targetIdx {
+			h := xxhash.Sum64String(inw.invoker.GetURL().String() + strconv.Itoa(len(items)))
+			items = append(items, &ringEntry{idx: idx, hash: h, invoker: inw.invoker})
+			idx++
+		}
+	}
+
+	// Sort items based on hash, to prepare for binary search.
+	sort.Slice(items, func(i, j int) bool { return items[i].hash < items[j].hash })
+	for i, ii := range items {
+		ii.idx = i
+	}
+	return items, nil
+}
+
+// normalizeWeights divides all the weights by the sum, so that the total weight
+// is 1.
+func normalizeWeights(invokers []invokerWrapper) ([]invokerWithWeight, float64, error) {
+	var weightSum int
+	for _, v := range invokers {
+		weightSum += v.weight
+	}
+	if weightSum == 0 {
+		return nil, 0, fmt.Errorf("total weight of all endpoints is 0")
+	}
+	weightSumF := float64(weightSum)
+	ret := make([]invokerWithWeight, 0, len(invokers))
+	min := math.MaxFloat64
+	for _, invoker := range invokers {
+		nw := float64(invoker.weight) / weightSumF
+		ret = append(ret, invokerWithWeight{invoker: invoker.invoker, weight: nw})
+		if nw < min {
+			min = nw
+		}
+	}
+	return ret, min, nil
+}
+
+func (lb *ringhashLoadBalance) pick(h uint64, items []*ringEntry) *ringEntry {
+	i := sort.Search(len(items), func(i int) bool { return items[i].hash >= h })
+	if i == len(items) {
+		// If not found, and h is greater than the largest hash, return the
+		// first item.
+		i = 0
+	}
+	return items[i]
+}
+
+func (lb *ringhashLoadBalance) generateHash(invocation protocol.Invocation, hashPolicies []*resource.HashPolicy) uint64 {
+	var hash uint64

Review Comment:
   放在一个 var () 里面



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