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// Copyright (C) 2019-2021 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package txnsync
import (
"container/heap"
"sort"
"time"
)
//msgp:ignore peerBuckets
type peerBuckets []peerBucket
type peerScheduler struct {
peers peerBuckets
nextPeers map[*Peer][]int // nextPeers holds an array of ordered indices where this Peer object is on the peers peerBuckets
node NodeConnector
}
// makePeerScheduler initializes a peer scheduler object.
func makePeerScheduler() peerScheduler {
return peerScheduler{
nextPeers: make(map[*Peer][]int),
}
}
//msgp:ignore peerBucket
type peerBucket struct {
peer *Peer
next time.Duration
}
// Push implements heap.Interface
func (p *peerScheduler) Push(x interface{}) {
entry := x.(peerBucket)
p.peers = append(p.peers, entry)
p.nextPeers[entry.peer] = append(p.nextPeers[entry.peer], len(p.peers)-1)
if len(p.nextPeers[entry.peer]) > 1 {
peerIndices := p.nextPeers[entry.peer]
sort.Slice(peerIndices, func(i, j int) bool {
return p.peers[peerIndices[i]].next < p.peers[peerIndices[j]].next
})
}
}
// Pop implements heap.Interface
func (p *peerScheduler) Pop() interface{} {
end := len(p.peers) - 1
res := p.peers[end]
// delete from the map only if it's the last entry
peerIndices := p.nextPeers[res.peer]
if peerIndices[0] != end {
// this case is possible when the peer has two elements in p.peers.
// and both have the same next value.
for idx, x := range peerIndices {
if x == end {
peerIndices[0], peerIndices[idx] = peerIndices[idx], peerIndices[0]
break
}
}
}
// the peer index must be the first entry.
peerIndices = peerIndices[1:]
// store if non-empty.
if len(peerIndices) > 0 {
p.nextPeers[res.peer] = peerIndices
} else {
delete(p.nextPeers, res.peer)
}
p.peers[end] = peerBucket{}
p.peers = p.peers[0:end]
return res
}
// Len implements heap.Interface
func (p *peerScheduler) Len() int {
return len(p.peers)
}
func (p *peerScheduler) replaceIndices(indices []int, i, j int) {
for idx, x := range indices {
if x == i {
indices[idx] = j
} else if x == j {
indices[idx] = i
}
}
sort.Slice(indices, func(i, j int) bool {
return p.peers[indices[i]].next < p.peers[indices[j]].next
})
}
// Swap implements heap.Interface
func (p *peerScheduler) Swap(i, j int) {
p.peers[i], p.peers[j] = p.peers[j], p.peers[i]
if p.peers[i].peer == p.peers[j].peer {
indices := p.nextPeers[p.peers[i].peer]
sort.Slice(indices, func(x, y int) bool {
return p.peers[indices[x]].next < p.peers[indices[y]].next
})
return
}
p.replaceIndices(p.nextPeers[p.peers[i].peer], i, j)
p.replaceIndices(p.nextPeers[p.peers[j].peer], i, j)
}
// Less implements heap.Interface
func (p *peerScheduler) Less(i, j int) bool {
return p.peers[i].next < p.peers[j].next
}
// refresh the current schedule by creating new schedule for each of the peers.
func (p *peerScheduler) scheduleNewRound(peers []*Peer) {
// clear the existings peers list.
p.peers = make(peerBuckets, 0, len(peers))
p.nextPeers = make(map[*Peer][]int)
for _, peer := range peers {
peerEntry := peerBucket{peer: peer}
peerEntry.next = kickoffTime + time.Duration(p.node.Random(uint64(randomRange)))
p.peers = append(p.peers, peerEntry)
p.nextPeers[peer] = []int{len(p.peers) - 1}
}
heap.Init(p)
}
func (p *peerScheduler) nextDuration() time.Duration {
if len(p.peers) == 0 {
return time.Duration(0)
}
return p.peers[0].next
}
func (p *peerScheduler) getNextPeers() (outPeers []*Peer) {
next := p.nextDuration()
// pull out of the heap all the entries that have next smaller or equal to the above next.
for len(p.peers) > 0 && p.peers[0].next <= next {
bucket := heap.Remove(p, 0).(peerBucket)
outPeers = append(outPeers, bucket.peer)
}
// in many cases, we'll have only a single peer; however, in case we have multiple
// ( which is more likely when we're "running late" ), we want to make sure to remove
// duplicate ones.
if len(outPeers) > 1 {
// note that the algorithm here ensures that we retain the peer order from above
// while dropping off recurring peers.
peersMap := make(map[*Peer]bool, len(outPeers))
offset := 0
peersMap[outPeers[0]] = true
for i := 1; i < len(outPeers); i++ {
if peersMap[outPeers[i]] {
// we already had this peer.
offset++
continue
}
// we haven't seen this peer.
outPeers[i-offset] = outPeers[i]
peersMap[outPeers[i]] = true
}
outPeers = outPeers[:len(outPeers)-offset]
}
return
}
func (p *peerScheduler) schedulePeer(peer *Peer, next time.Duration) {
bucket := peerBucket{peer: peer, next: next}
heap.Push(p, bucket)
}
func (p *peerScheduler) peerDuration(peer *Peer) time.Duration {
peerIndices := p.nextPeers[peer]
if len(peerIndices) == 0 {
return time.Duration(0)
}
bucket := heap.Remove(p, peerIndices[0]).(peerBucket)
return bucket.next
}
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