forked from scionproto/scion
-
Notifications
You must be signed in to change notification settings - Fork 0
/
selection_algo.go
118 lines (106 loc) · 3.67 KB
/
selection_algo.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
// Copyright 2019 Anapaya Systems
//
// 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 beacon
import "math"
type selectionAlgorithm interface {
// SelectAndServe selects the n best beacons from the beacons channel and
// serves them on the results channel.
SelectAndServe(beacons <-chan BeaconOrErr, results chan<- BeaconOrErr, resultSize int)
}
// baseAlgo implements a very simple selection algorithm that optimizes for
// short paths, but also tries to achieve some path diversity.
type baseAlgo struct{}
// selectAndServe implements a very simple selection algorithm. The best beacon
// is the one with a shortest path. The channel is filled with the k-1 shortest
// beacons. The last beacon is either the most diverse beacon from the remaining
// beacons, if the diversity exceeds what has already been served. Or the
// shortest remaining beacon, otherswise.
func (baseAlgo) SelectAndServe(beacons <-chan BeaconOrErr, results chan<- BeaconOrErr,
resultSize int) {
best, diversity := baseAlgo{}.serveShortestBeacons(beacons, results, resultSize-1)
baseAlgo{}.serveMostDiverse(beacons, results, best, diversity)
}
// serveShortsestBeacons serves the resultSize shortest beacons on the result channel.
// It returns the first beacon and the maximum served diversity.
func (baseAlgo) serveShortestBeacons(beacons <-chan BeaconOrErr, results chan<- BeaconOrErr,
resultSize int) (Beacon, int) {
var best Beacon
var maxDiversity int
i := 0
for res := range beacons {
if res.Err == nil {
if (best == Beacon{}) {
// Create shallow copy to avoid data race.
best = Beacon{
Segment: res.Beacon.Segment.ShallowCopy(),
InIfId: res.Beacon.InIfId,
}
}
// Compute diversity before serving beacon to avoid data race.
maxDiversity = max(maxDiversity, best.Diversity(res.Beacon))
i++
}
results <- res
if i == resultSize {
break
}
}
return best, maxDiversity
}
// serveMostDiverse selects the most diverse beacon compared to the provided
// best beacon from all beacons that are in the channel and serves it in the
// result channel if it exceeds the already served diversity. Otherwise, the
// shortest beacon is served.
func (baseAlgo) serveMostDiverse(beacons <-chan BeaconOrErr, results chan<- BeaconOrErr,
best Beacon, servedDiversity int) {
var err error
// Most diverse beacon of the remaining beacons.
var diverse Beacon
maxDiversity := -1
minLen := math.MaxUint16
// First is the shortest beacon and selected if the diversity is below the
// already served diversity.
var first Beacon
for res := range beacons {
if (first == Beacon{}) {
first = res.Beacon
}
if res.Err != nil {
err = res.Err
continue
}
diversity := best.Diversity(res.Beacon)
l := len(res.Beacon.Segment.ASEntries)
if diversity > maxDiversity || (diversity == maxDiversity && minLen > l) {
diverse, minLen, maxDiversity = res.Beacon, l, diversity
}
}
if (first == Beacon{}) {
if err != nil {
results <- BeaconOrErr{Err: err}
}
return
}
if (diverse != Beacon{}) && maxDiversity > servedDiversity {
results <- BeaconOrErr{Beacon: diverse}
return
}
results <- BeaconOrErr{Beacon: first}
}
func max(a, b int) int {
if a > b {
return a
}
return b
}