requesting.go

   1 package torrent
   2
   3 import (
   4         "container/heap"
   5         "context"
   6         "encoding/gob"
   7         "fmt"
   8         "reflect"
   9         "runtime/pprof"
  10         "time"
  11         "unsafe"
  12
  13         "github.com/anacrolix/log"
  14         "github.com/anacrolix/multiless"
  15
  16         request_strategy "github.com/anacrolix/torrent/request-strategy"
  17 )
  18
  19 func (t *Torrent) requestStrategyPieceOrderState(i int) request_strategy.PieceRequestOrderState {
  20         return request_strategy.PieceRequestOrderState{
  21                 Priority:     t.piece(i).purePriority(),
  22                 Partial:      t.piecePartiallyDownloaded(i),
  23                 Availability: t.piece(i).availability(),
  24         }
  25 }
  26
  27 func init() {
  28         gob.Register(peerId{})
  29 }
  30
  31 type peerId struct {
  32         *Peer
  33         ptr uintptr
  34 }
  35
  36 func (p peerId) Uintptr() uintptr {
  37         return p.ptr
  38 }
  39
  40 func (p peerId) GobEncode() (b []byte, _ error) {
  41         *(*reflect.SliceHeader)(unsafe.Pointer(&b)) = reflect.SliceHeader{
  42                 Data: uintptr(unsafe.Pointer(&p.ptr)),
  43                 Len:  int(unsafe.Sizeof(p.ptr)),
  44                 Cap:  int(unsafe.Sizeof(p.ptr)),
  45         }
  46         return
  47 }
  48
  49 func (p *peerId) GobDecode(b []byte) error {
  50         if uintptr(len(b)) != unsafe.Sizeof(p.ptr) {
  51                 panic(len(b))
  52         }
  53         ptr := unsafe.Pointer(&b[0])
  54         p.ptr = *(*uintptr)(ptr)
  55         log.Printf("%p", ptr)
  56         dst := reflect.SliceHeader{
  57                 Data: uintptr(unsafe.Pointer(&p.Peer)),
  58                 Len:  int(unsafe.Sizeof(p.Peer)),
  59                 Cap:  int(unsafe.Sizeof(p.Peer)),
  60         }
  61         copy(*(*[]byte)(unsafe.Pointer(&dst)), b)
  62         return nil
  63 }
  64
  65 type (
  66         RequestIndex   = request_strategy.RequestIndex
  67         chunkIndexType = request_strategy.ChunkIndex
  68 )
  69
  70 type desiredPeerRequests struct {
  71         requestIndexes []RequestIndex
  72         peer           *Peer
  73 }
  74
  75 func (p *desiredPeerRequests) Len() int {
  76         return len(p.requestIndexes)
  77 }
  78
  79 func (p *desiredPeerRequests) Less(i, j int) bool {
  80         leftRequest := p.requestIndexes[i]
  81         rightRequest := p.requestIndexes[j]
  82         t := p.peer.t
  83         leftPieceIndex := t.pieceIndexOfRequestIndex(leftRequest)
  84         rightPieceIndex := t.pieceIndexOfRequestIndex(rightRequest)
  85         ml := multiless.New()
  86         // Push requests that can't be served right now to the end. But we don't throw them away unless
  87         // there's a better alternative. This is for when we're using the fast extension and get choked
  88         // but our requests could still be good when we get unchoked.
  89         if p.peer.peerChoking {
  90                 ml = ml.Bool(
  91                         !p.peer.peerAllowedFast.Contains(leftPieceIndex),
  92                         !p.peer.peerAllowedFast.Contains(rightPieceIndex),
  93                 )
  94         }
  95         leftPiece := t.piece(leftPieceIndex)
  96         rightPiece := t.piece(rightPieceIndex)
  97         // Putting this first means we can steal requests from lesser-performing peers for our first few
  98         // new requests.
  99         priority := func() piecePriority {
 100                 // Technically we would be happy with the cached priority here, except we don't actually
 101                 // cache it anymore, and Torrent.piecePriority just does another lookup of *Piece to resolve
 102                 // the priority through Piece.purePriority, which is probably slower.
 103                 leftPriority := leftPiece.purePriority()
 104                 rightPriority := rightPiece.purePriority()
 105                 ml = ml.Int(
 106                         -int(leftPriority),
 107                         -int(rightPriority),
 108                 )
 109                 if !ml.Ok() {
 110                         if leftPriority != rightPriority {
 111                                 panic("expected equal")
 112                         }
 113                 }
 114                 return leftPriority
 115         }()
 116         if ml.Ok() {
 117                 return ml.MustLess()
 118         }
 119         leftPeer := t.pendingRequests[leftRequest]
 120         rightPeer := t.pendingRequests[rightRequest]
 121         // Prefer chunks already requested from this peer.
 122         ml = ml.Bool(rightPeer == p.peer, leftPeer == p.peer)
 123         // Prefer unrequested chunks.
 124         ml = ml.Bool(rightPeer == nil, leftPeer == nil)
 125         if ml.Ok() {
 126                 return ml.MustLess()
 127         }
 128         if leftPeer != nil {
 129                 // The right peer should also be set, or we'd have resolved the computation by now.
 130                 ml = ml.Uint64(
 131                         rightPeer.requestState.Requests.GetCardinality(),
 132                         leftPeer.requestState.Requests.GetCardinality(),
 133                 )
 134                 // Could either of the lastRequested be Zero? That's what checking an existing peer is for.
 135                 leftLast := t.lastRequested[leftRequest]
 136                 rightLast := t.lastRequested[rightRequest]
 137                 if leftLast.IsZero() || rightLast.IsZero() {
 138                         panic("expected non-zero last requested times")
 139                 }
 140                 // We want the most-recently requested on the left. Clients like Transmission serve requests
 141                 // in received order, so the most recently-requested is the one that has the longest until
 142                 // it will be served and therefore is the best candidate to cancel.
 143                 ml = ml.CmpInt64(rightLast.Sub(leftLast).Nanoseconds())
 144         }
 145         ml = ml.Int(
 146                 leftPiece.relativeAvailability,
 147                 rightPiece.relativeAvailability)
 148         if priority == PiecePriorityReadahead {
 149                 // TODO: For readahead in particular, it would be even better to consider distance from the
 150                 // reader position so that reads earlier in a torrent don't starve reads later in the
 151                 // torrent. This would probably require reconsideration of how readahead priority works.
 152                 ml = ml.Int(leftPieceIndex, rightPieceIndex)
 153         } else {
 154                 // TODO: To prevent unnecessarily requesting from disparate pieces, and to ensure pieces are
 155                 // selected randomly when availability is even, there should be some fixed ordering of
 156                 // pieces.
 157         }
 158         return ml.Less()
 159 }
 160
 161 func (p *desiredPeerRequests) Swap(i, j int) {
 162         p.requestIndexes[i], p.requestIndexes[j] = p.requestIndexes[j], p.requestIndexes[i]
 163 }
 164
 165 func (p *desiredPeerRequests) Push(x interface{}) {
 166         p.requestIndexes = append(p.requestIndexes, x.(RequestIndex))
 167 }
 168
 169 func (p *desiredPeerRequests) Pop() interface{} {
 170         last := len(p.requestIndexes) - 1
 171         x := p.requestIndexes[last]
 172         p.requestIndexes = p.requestIndexes[:last]
 173         return x
 174 }
 175
 176 type desiredRequestState struct {
 177         Requests   desiredPeerRequests
 178         Interested bool
 179 }
 180
 181 func (p *Peer) getDesiredRequestState() (desired desiredRequestState) {
 182         if !p.t.haveInfo() {
 183                 return
 184         }
 185         if p.t.closed.IsSet() {
 186                 return
 187         }
 188         input := p.t.getRequestStrategyInput()
 189         requestHeap := desiredPeerRequests{
 190                 peer: p,
 191         }
 192         request_strategy.GetRequestablePieces(
 193                 input,
 194                 p.t.getPieceRequestOrder(),
 195                 func(ih InfoHash, pieceIndex int) {
 196                         if ih != p.t.infoHash {
 197                                 return
 198                         }
 199                         if !p.peerHasPiece(pieceIndex) {
 200                                 return
 201                         }
 202                         allowedFast := p.peerAllowedFast.Contains(pieceIndex)
 203                         p.t.piece(pieceIndex).undirtiedChunksIter.Iter(func(ci request_strategy.ChunkIndex) {
 204                                 r := p.t.pieceRequestIndexOffset(pieceIndex) + ci
 205                                 if !allowedFast {
 206                                         // We must signal interest to request this. TODO: We could set interested if the
 207                                         // peers pieces (minus the allowed fast set) overlap with our missing pieces if
 208                                         // there are any readers, or any pending pieces.
 209                                         desired.Interested = true
 210                                         // We can make or will allow sustaining a request here if we're not choked, or
 211                                         // have made the request previously (presumably while unchoked), and haven't had
 212                                         // the peer respond yet (and the request was retained because we are using the
 213                                         // fast extension).
 214                                         if p.peerChoking && !p.requestState.Requests.Contains(r) {
 215                                                 // We can't request this right now.
 216                                                 return
 217                                         }
 218                                 }
 219                                 if p.requestState.Cancelled.Contains(r) {
 220                                         // Can't re-request while awaiting acknowledgement.
 221                                         return
 222                                 }
 223                                 requestHeap.requestIndexes = append(requestHeap.requestIndexes, r)
 224                         })
 225                 },
 226         )
 227         p.t.assertPendingRequests()
 228         desired.Requests = requestHeap
 229         return
 230 }
 231
 232 func (p *Peer) maybeUpdateActualRequestState() {
 233         if p.closed.IsSet() {
 234                 return
 235         }
 236         if p.needRequestUpdate == "" {
 237                 return
 238         }
 239         if p.needRequestUpdate == peerUpdateRequestsTimerReason {
 240                 since := time.Since(p.lastRequestUpdate)
 241                 if since < updateRequestsTimerDuration {
 242                         panic(since)
 243                 }
 244         }
 245         pprof.Do(
 246                 context.Background(),
 247                 pprof.Labels("update request", p.needRequestUpdate),
 248                 func(_ context.Context) {
 249                         next := p.getDesiredRequestState()
 250                         p.applyRequestState(next)
 251                 },
 252         )
 253 }
 254
 255 // Transmit/action the request state to the peer.
 256 func (p *Peer) applyRequestState(next desiredRequestState) {
 257         current := &p.requestState
 258         if !p.setInterested(next.Interested) {
 259                 panic("insufficient write buffer")
 260         }
 261         more := true
 262         requestHeap := &next.Requests
 263         t := p.t
 264         originalRequestCount := current.Requests.GetCardinality()
 265         // We're either here on a timer, or because we ran out of requests. Both are valid reasons to
 266         // alter peakRequests.
 267         if originalRequestCount != 0 && p.needRequestUpdate != peerUpdateRequestsTimerReason {
 268                 panic(fmt.Sprintf(
 269                         "expected zero existing requests (%v) for update reason %q",
 270                         originalRequestCount, p.needRequestUpdate))
 271         }
 272         heap.Init(requestHeap)
 273         for requestHeap.Len() != 0 && maxRequests(current.Requests.GetCardinality()+current.Cancelled.GetCardinality()) < p.nominalMaxRequests() {
 274                 req := heap.Pop(requestHeap).(RequestIndex)
 275                 existing := t.requestingPeer(req)
 276                 if existing != nil && existing != p {
 277                         // Don't steal from the poor.
 278                         diff := int64(current.Requests.GetCardinality()) + 1 - (int64(existing.uncancelledRequests()) - 1)
 279                         // Steal a request that leaves us with one more request than the existing peer
 280                         // connection if the stealer more recently received a chunk.
 281                         if diff > 1 || (diff == 1 && p.lastUsefulChunkReceived.Before(existing.lastUsefulChunkReceived)) {
 282                                 continue
 283                         }
 284                         t.cancelRequest(req)
 285                 }
 286                 more = p.mustRequest(req)
 287                 if !more {
 288                         break
 289                 }
 290         }
 291         if !more {
 292                 // This might fail if we incorrectly determine that we can fit up to the maximum allowed
 293                 // requests into the available write buffer space. We don't want that to happen because it
 294                 // makes our peak requests dependent on how much was already in the buffer.
 295                 panic(fmt.Sprintf(
 296                         "couldn't fill apply entire request state [newRequests=%v]",
 297                         current.Requests.GetCardinality()-originalRequestCount))
 298         }
 299         newPeakRequests := maxRequests(current.Requests.GetCardinality() - originalRequestCount)
 300         // log.Printf(
 301         //      "requests %v->%v (peak %v->%v) reason %q (peer %v)",
 302         //      originalRequestCount, current.Requests.GetCardinality(), p.peakRequests, newPeakRequests, p.needRequestUpdate, p)
 303         p.peakRequests = newPeakRequests
 304         p.needRequestUpdate = ""
 305         p.lastRequestUpdate = time.Now()
 306         p.updateRequestsTimer.Reset(updateRequestsTimerDuration)
 307 }
 308
 309 // This could be set to 10s to match the unchoke/request update interval recommended by some
 310 // specifications. I've set it shorter to trigger it more often for testing for now.
 311 const updateRequestsTimerDuration = 3 * time.Second