github.com/uber/kraken@v0.1.4/lib/torrent/scheduler/dispatch/piecerequest/rarest_first_policy.go (about)

     1  // Copyright (c) 2016-2019 Uber Technologies, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  package piecerequest
    15  
    16  import (
    17  	"github.com/uber/kraken/utils/heap"
    18  	"github.com/uber/kraken/utils/syncutil"
    19  
    20  	"github.com/willf/bitset"
    21  )
    22  
    23  // RarestFirstPolicy selects pieces that the fewest of our peers have to request first.
    24  const RarestFirstPolicy = "rarest_first"
    25  
    26  type rarestFirstPolicy struct{}
    27  
    28  func newRarestFirstPolicy() *rarestFirstPolicy {
    29  	return &rarestFirstPolicy{}
    30  }
    31  
    32  func (p *rarestFirstPolicy) selectPieces(
    33  	limit int,
    34  	valid func(int) bool,
    35  	candidates *bitset.BitSet,
    36  	numPeersByPiece syncutil.Counters) ([]int, error) {
    37  
    38  	candidateQueue := heap.NewPriorityQueue()
    39  	for i, e := candidates.NextSet(0); e; i, e = candidates.NextSet(i + 1) {
    40  		candidateQueue.Push(&heap.Item{
    41  			Value:    int(i),
    42  			Priority: numPeersByPiece.Get(int(i)),
    43  		})
    44  	}
    45  
    46  	pieces := make([]int, 0, limit)
    47  	for len(pieces) < limit && candidateQueue.Len() > 0 {
    48  		item, err := candidateQueue.Pop()
    49  		if err != nil {
    50  			return nil, err
    51  		}
    52  
    53  		candidate := item.Value.(int)
    54  		if valid(candidate) {
    55  			pieces = append(pieces, candidate)
    56  		}
    57  	}
    58  
    59  	return pieces, nil
    60  }