forked from uber/kraken
/
rarest_first_policy.go
60 lines (50 loc) · 1.63 KB
/
rarest_first_policy.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
// Copyright (c) 2016-2019 Uber Technologies, Inc.
//
// 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 piecerequest
import (
"github.com/uber/kraken/utils/heap"
"github.com/uber/kraken/utils/syncutil"
"github.com/willf/bitset"
)
// RarestFirstPolicy selects pieces that the fewest of our peers have to request first.
const RarestFirstPolicy = "rarest_first"
type rarestFirstPolicy struct{}
func newRarestFirstPolicy() *rarestFirstPolicy {
return &rarestFirstPolicy{}
}
func (p *rarestFirstPolicy) selectPieces(
limit int,
valid func(int) bool,
candidates *bitset.BitSet,
numPeersByPiece syncutil.Counters) ([]int, error) {
candidateQueue := heap.NewPriorityQueue()
for i, e := candidates.NextSet(0); e; i, e = candidates.NextSet(i + 1) {
candidateQueue.Push(&heap.Item{
Value: int(i),
Priority: numPeersByPiece.Get(int(i)),
})
}
pieces := make([]int, 0, limit)
for len(pieces) < limit && candidateQueue.Len() > 0 {
item, err := candidateQueue.Pop()
if err != nil {
return nil, err
}
candidate := item.Value.(int)
if valid(candidate) {
pieces = append(pieces, candidate)
}
}
return pieces, nil
}