google.golang.org/grpc@v1.72.2/internal/wrr/random.go (about)

     1  /*
     2   *
     3   * Copyright 2019 gRPC authors.
     4   *
     5   * Licensed under the Apache License, Version 2.0 (the "License");
     6   * you may not use this file except in compliance with the License.
     7   * You may obtain a copy of the License at
     8   *
     9   *     http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17  
    18  package wrr
    19  
    20  import (
    21  	"fmt"
    22  	rand "math/rand/v2"
    23  	"sort"
    24  )
    25  
    26  // weightedItem is a wrapped weighted item that is used to implement weighted random algorithm.
    27  type weightedItem struct {
    28  	item              any
    29  	weight            int64
    30  	accumulatedWeight int64
    31  }
    32  
    33  func (w *weightedItem) String() string {
    34  	return fmt.Sprint(*w)
    35  }
    36  
    37  // randomWRR is a struct that contains weighted items implement weighted random algorithm.
    38  type randomWRR struct {
    39  	items []*weightedItem
    40  	// Are all item's weights equal
    41  	equalWeights bool
    42  }
    43  
    44  // NewRandom creates a new WRR with random.
    45  func NewRandom() WRR {
    46  	return &randomWRR{}
    47  }
    48  
    49  var randInt64n = rand.Int64N
    50  
    51  func (rw *randomWRR) Next() (item any) {
    52  	if len(rw.items) == 0 {
    53  		return nil
    54  	}
    55  	if rw.equalWeights {
    56  		return rw.items[randInt64n(int64(len(rw.items)))].item
    57  	}
    58  
    59  	sumOfWeights := rw.items[len(rw.items)-1].accumulatedWeight
    60  	// Random number in [0, sumOfWeights).
    61  	randomWeight := randInt64n(sumOfWeights)
    62  	// Item's accumulated weights are in ascending order, because item's weight >= 0.
    63  	// Binary search rw.items to find first item whose accumulatedWeight > randomWeight
    64  	// The return i is guaranteed to be in range [0, len(rw.items)) because randomWeight < last item's accumulatedWeight
    65  	i := sort.Search(len(rw.items), func(i int) bool { return rw.items[i].accumulatedWeight > randomWeight })
    66  	return rw.items[i].item
    67  }
    68  
    69  func (rw *randomWRR) Add(item any, weight int64) {
    70  	accumulatedWeight := weight
    71  	equalWeights := true
    72  	if len(rw.items) > 0 {
    73  		lastItem := rw.items[len(rw.items)-1]
    74  		accumulatedWeight = lastItem.accumulatedWeight + weight
    75  		equalWeights = rw.equalWeights && weight == lastItem.weight
    76  	}
    77  	rw.equalWeights = equalWeights
    78  	rItem := &weightedItem{item: item, weight: weight, accumulatedWeight: accumulatedWeight}
    79  	rw.items = append(rw.items, rItem)
    80  }
    81  
    82  func (rw *randomWRR) String() string {
    83  	return fmt.Sprint(rw.items)
    84  }