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/*
*
* 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"
"sort"
"sync"
"google.golang.org/grpc/internal/grpcrand"
)
// weightedItem is a wrapped weighted item that is used to implement weighted random algorithm.
type weightedItem struct {
item interface{}
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 {
mu sync.RWMutex
items []*weightedItem
// Are all item's weights equal
equalWeights bool
}
// NewRandom creates a new WRR with random.
func NewRandom() WRR {
return &randomWRR{}
}
var grpcrandInt63n = grpcrand.Int63n
func (rw *randomWRR) Next() (item interface{}) {
rw.mu.RLock()
defer rw.mu.RUnlock()
if len(rw.items) == 0 {
return nil
}
if rw.equalWeights {
return rw.items[grpcrandInt63n(int64(len(rw.items)))].item
}
sumOfWeights := rw.items[len(rw.items)-1].accumulatedWeight
// Random number in [0, sumOfWeights).
randomWeight := grpcrandInt63n(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 interface{}, weight int64) {
rw.mu.Lock()
defer rw.mu.Unlock()
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)
}
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