-
Notifications
You must be signed in to change notification settings - Fork 792
/
weighted_round_robin.go
165 lines (145 loc) · 4.16 KB
/
weighted_round_robin.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
/*
* Copyright 2023 CloudWeGo 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 loadbalance
import (
"context"
"sync"
"github.com/bytedance/gopkg/lang/fastrand"
"github.com/cloudwego/kitex/pkg/discovery"
)
var (
_ Picker = &WeightedRoundRobinPicker{}
_ Picker = &RoundRobinPicker{}
)
const wrrVNodesBatchSize = 500 // it will calculate wrrVNodesBatchSize vnodes when insufficient
type wrrNode struct {
discovery.Instance
current int
}
func newWeightedRoundRobinPicker(instances []discovery.Instance) Picker {
wrrp := new(WeightedRoundRobinPicker)
wrrp.iterator = newRound()
// shuffle nodes
wrrp.size = uint64(len(instances))
wrrp.nodes = make([]*wrrNode, wrrp.size)
offset := fastrand.Uint64n(wrrp.size)
totalWeight := 0
gcd := 0
for idx := uint64(0); idx < wrrp.size; idx++ {
ins := instances[(idx+offset)%wrrp.size]
totalWeight += ins.Weight()
gcd = gcdInt(gcd, ins.Weight())
wrrp.nodes[idx] = &wrrNode{
Instance: ins,
current: 0,
}
}
wrrp.vcapacity = uint64(totalWeight / gcd)
wrrp.vnodes = make([]discovery.Instance, wrrp.vcapacity)
wrrp.buildVirtualWrrNodes(wrrVNodesBatchSize)
return wrrp
}
// WeightedRoundRobinPicker implement smooth weighted round-robin algorithm.
// Refer from https://github.com/phusion/nginx/commit/27e94984486058d73157038f7950a0a36ecc6e35
type WeightedRoundRobinPicker struct {
nodes []*wrrNode // instance node with current weight
size uint64 // size of wrrNodes
iterator *round
vsize uint64 // size of valid vnodes
vcapacity uint64 // capacity of all vnodes
vnodes []discovery.Instance // precalculated vnodes which order by swrr algorithm
vlock sync.RWMutex // mutex for vnodes
}
// Next implements the Picker interface.
func (wp *WeightedRoundRobinPicker) Next(ctx context.Context, request interface{}) (ins discovery.Instance) {
// iterator must start from 0, because we need warmup the vnode at beginning
idx := wp.iterator.Next() % wp.vcapacity
// fast path
wp.vlock.RLock()
ins = wp.vnodes[idx]
wp.vlock.RUnlock()
if ins != nil {
return ins
}
// slow path
wp.vlock.Lock()
defer wp.vlock.Unlock()
if wp.vnodes[idx] != nil { // other goroutine has filled the vnodes
return wp.vnodes[idx]
}
vtarget := wp.vsize + wrrVNodesBatchSize
// we must promise that idx < vtarget
if idx >= vtarget {
vtarget = idx + 1
}
wp.buildVirtualWrrNodes(vtarget)
return wp.vnodes[idx]
}
func (wp *WeightedRoundRobinPicker) buildVirtualWrrNodes(vtarget uint64) {
if vtarget > wp.vcapacity {
vtarget = wp.vcapacity
}
for i := wp.vsize; i < vtarget; i++ {
wp.vnodes[i] = nextWrrNode(wp.nodes).Instance
}
wp.vsize = vtarget
}
func nextWrrNode(nodes []*wrrNode) (selected *wrrNode) {
maxCurrent := 0
totalWeight := 0
for _, node := range nodes {
node.current += node.Weight()
totalWeight += node.Weight()
if selected == nil || node.current > maxCurrent {
selected = node
maxCurrent = node.current
}
}
if selected == nil {
return nil
}
selected.current -= totalWeight
return selected
}
// RoundRobinPicker .
type RoundRobinPicker struct {
size uint64
instances []discovery.Instance
iterator *round
}
func newRoundRobinPicker(instances []discovery.Instance) Picker {
size := uint64(len(instances))
return &RoundRobinPicker{
size: size,
instances: instances,
iterator: newRandomRound(),
}
}
// Next implements the Picker interface.
func (rp *RoundRobinPicker) Next(ctx context.Context, request interface{}) (ins discovery.Instance) {
if rp.size == 0 {
return nil
}
idx := rp.iterator.Next() % rp.size
ins = rp.instances[idx]
return ins
}
func gcdInt(a, b int) int {
for b != 0 {
a, b = b, a%b
}
return a
}