1 /* Copyright (c) 2012-2020. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
10 #include "s4u-peer.hpp"
11 #include "s4u-tracker.hpp"
13 XBT_LOG_NEW_DEFAULT_CATEGORY(s4u_bt_peer, "Messages specific for the peers");
16 * User parameters for transferred file data. For the test, the default values are :
17 * File size: 10 pieces * 5 blocks/piece * 16384 bytes/block = 819200 bytes
19 constexpr unsigned long FILE_PIECES = 10UL;
20 constexpr unsigned long PIECES_BLOCKS = 5UL;
21 constexpr int BLOCK_SIZE = 16384;
23 /** Number of blocks asked by each request */
24 constexpr unsigned long BLOCKS_REQUESTED = 2UL;
26 constexpr double SLEEP_DURATION = 1.0;
27 #define BITS_TO_BYTES(x) (((x) / 8 + (x) % 8) ? 1 : 0)
29 Peer::Peer(std::vector<std::string> args)
32 xbt_assert(args.size() == 3 || args.size() == 4, "Wrong number of arguments");
34 id = std::stoi(args[1]);
35 mailbox_ = simgrid::s4u::Mailbox::by_name(std::to_string(id));
36 } catch (const std::invalid_argument&) {
37 throw std::invalid_argument("Invalid ID:" + args[1]);
42 deadline = std::stod(args[2]);
43 } catch (const std::invalid_argument&) {
44 throw std::invalid_argument("Invalid deadline:" + args[2]);
46 xbt_assert(deadline > 0, "Wrong deadline supplied");
48 if (args.size() == 4 && args[3] == "1") {
49 bitfield_ = (1U << FILE_PIECES) - 1U;
50 bitfield_blocks = (1ULL << (FILE_PIECES * PIECES_BLOCKS)) - 1ULL;
52 pieces_count.resize(FILE_PIECES);
54 XBT_INFO("Hi, I'm joining the network with id %d", id);
57 /** Peer main function */
58 void Peer::operator()()
60 // Getting peer data from the tracker.
61 if (getPeersFromTracker()) {
62 XBT_DEBUG("Got %zu peers from the tracker. Current status is: %s", connected_peers.size(), getStatus().c_str());
63 begin_receive_time = simgrid::s4u::Engine::get_clock();
64 mailbox_->set_receiver(simgrid::s4u::Actor::self());
66 sendHandshakeToAllPeers();
72 XBT_INFO("Couldn't contact the tracker.");
75 XBT_INFO("Here is my current status: %s", getStatus().c_str());
78 bool Peer::getPeersFromTracker()
80 simgrid::s4u::Mailbox* tracker_mailbox = simgrid::s4u::Mailbox::by_name(TRACKER_MAILBOX);
81 // Build the task to send to the tracker
82 auto* peer_request = new TrackerQuery(id, mailbox_);
84 XBT_DEBUG("Sending a peer request to the tracker.");
85 tracker_mailbox->put(peer_request, TRACKER_COMM_SIZE, GET_PEERS_TIMEOUT);
86 } catch (const simgrid::TimeoutException&) {
87 XBT_DEBUG("Timeout expired when requesting peers to tracker");
93 auto* answer = static_cast<TrackerAnswer*>(mailbox_->get(GET_PEERS_TIMEOUT));
94 // Add the peers the tracker gave us to our peer list.
95 for (auto const& peer_id : answer->getPeers())
97 connected_peers.emplace(peer_id, Connection(peer_id));
99 } catch (const simgrid::TimeoutException&) {
100 XBT_DEBUG("Timeout expired when requesting peers to tracker");
106 void Peer::sendHandshakeToAllPeers()
108 for (auto const& kv : connected_peers) {
109 const Connection& remote_peer = kv.second;
110 auto* handshake = new Message(MESSAGE_HANDSHAKE, id, mailbox_);
111 remote_peer.mailbox_->put_init(handshake, MESSAGE_HANDSHAKE_SIZE)->detach();
112 XBT_DEBUG("Sending a HANDSHAKE to %d", remote_peer.id);
116 void Peer::sendMessage(simgrid::s4u::Mailbox* mailbox, e_message_type type, uint64_t size)
118 constexpr std::array<const char*, 6> type_names{
119 {"HANDSHAKE", "CHOKE", "UNCHOKE", "INTERESTED", "NOTINTERESTED", "CANCEL"}};
120 XBT_DEBUG("Sending %s to %s", type_names[type], mailbox->get_cname());
121 mailbox->put_init(new Message(type, id, bitfield_, mailbox_), size)->detach();
124 void Peer::sendBitfield(simgrid::s4u::Mailbox* mailbox)
126 XBT_DEBUG("Sending a BITFIELD to %s", mailbox->get_cname());
128 ->put_init(new Message(MESSAGE_BITFIELD, id, bitfield_, mailbox_),
129 MESSAGE_BITFIELD_SIZE + BITS_TO_BYTES(FILE_PIECES))
133 void Peer::sendPiece(simgrid::s4u::Mailbox* mailbox, unsigned int piece, int block_index, int block_length)
135 xbt_assert(not hasNotPiece(piece), "Tried to send a unavailable piece.");
136 XBT_DEBUG("Sending the PIECE %u (%d,%d) to %s", piece, block_index, block_length, mailbox->get_cname());
137 mailbox->put_init(new Message(MESSAGE_PIECE, id, mailbox_, piece, block_index, block_length), BLOCK_SIZE)->detach();
140 void Peer::sendHaveToAllPeers(unsigned int piece)
142 XBT_DEBUG("Sending HAVE message to all my peers");
143 for (auto const& kv : connected_peers) {
144 const Connection& remote_peer = kv.second;
145 remote_peer.mailbox_->put_init(new Message(MESSAGE_HAVE, id, mailbox_, piece), MESSAGE_HAVE_SIZE)->detach();
149 void Peer::sendRequestTo(Connection* remote_peer, unsigned int piece)
151 remote_peer->current_piece = piece;
152 xbt_assert(remote_peer->hasPiece(piece));
153 int block_index = getFirstMissingBlockFrom(piece);
154 if (block_index != -1) {
155 int block_length = static_cast<int>(std::min(BLOCKS_REQUESTED, PIECES_BLOCKS - block_index));
156 XBT_DEBUG("Sending a REQUEST to %s for piece %u (%d,%d)", remote_peer->mailbox_->get_cname(), piece, block_index,
158 remote_peer->mailbox_
159 ->put_init(new Message(MESSAGE_REQUEST, id, mailbox_, piece, block_index, block_length), MESSAGE_REQUEST_SIZE)
164 std::string Peer::getStatus() const
167 for (unsigned i = 0; i < FILE_PIECES; i++)
168 res += (bitfield_ & (1U << i)) ? '1' : '0';
172 bool Peer::hasFinished() const
174 return bitfield_ == (1U << FILE_PIECES) - 1U;
177 /** Indicates if the remote peer has a piece not stored by the local peer */
178 bool Peer::isInterestedBy(const Connection* remote_peer) const
180 return remote_peer->bitfield & (bitfield_ ^ ((1 << FILE_PIECES) - 1));
183 bool Peer::isInterestedByFree(const Connection* remote_peer) const
185 for (unsigned int i = 0; i < FILE_PIECES; i++)
186 if (hasNotPiece(i) && remote_peer->hasPiece(i) && isNotDownloadingPiece(i))
191 void Peer::updatePiecesCountFromBitfield(unsigned int bitfield)
193 for (unsigned int i = 0; i < FILE_PIECES; i++)
194 if (bitfield & (1U << i))
198 unsigned int Peer::countPieces(unsigned int bitfield) const
200 unsigned int count = 0U;
201 unsigned int n = bitfield;
209 int Peer::nbInterestedPeers() const
212 for (auto const& kv : connected_peers)
213 if (kv.second.interested)
220 double next_choked_update = simgrid::s4u::Engine::get_clock() + UPDATE_CHOKED_INTERVAL;
221 XBT_DEBUG("Start downloading.");
223 /* Send a "handshake" message to all the peers it got (since it couldn't have gotten more than 50 peers) */
224 sendHandshakeToAllPeers();
225 XBT_DEBUG("Starting main leech loop listening on mailbox: %s", mailbox_->get_cname());
227 void* data = nullptr;
228 while (simgrid::s4u::Engine::get_clock() < deadline && countPieces(bitfield_) < FILE_PIECES) {
229 if (comm_received == nullptr) {
230 comm_received = mailbox_->get_async(&data);
232 if (comm_received->test()) {
233 message = static_cast<Message*>(data);
236 comm_received = nullptr;
238 // We don't execute the choke algorithm if we don't already have a piece
239 if (simgrid::s4u::Engine::get_clock() >= next_choked_update && countPieces(bitfield_) > 0) {
241 next_choked_update += UPDATE_CHOKED_INTERVAL;
243 simgrid::s4u::this_actor::sleep_for(SLEEP_DURATION);
248 XBT_DEBUG("%d becomes a seeder", id);
253 double next_choked_update = simgrid::s4u::Engine::get_clock() + UPDATE_CHOKED_INTERVAL;
254 XBT_DEBUG("Start seeding.");
255 // start the main seed loop
256 void* data = nullptr;
257 while (simgrid::s4u::Engine::get_clock() < deadline) {
258 if (comm_received == nullptr) {
259 comm_received = mailbox_->get_async(&data);
261 if (comm_received->test()) {
262 message = static_cast<Message*>(data);
265 comm_received = nullptr;
267 if (simgrid::s4u::Engine::get_clock() >= next_choked_update) {
269 // TODO: Change the choked peer algorithm when seeding.
270 next_choked_update += UPDATE_CHOKED_INTERVAL;
272 simgrid::s4u::this_actor::sleep_for(SLEEP_DURATION);
278 void Peer::updateActivePeersSet(Connection* remote_peer)
280 if (remote_peer->interested && not remote_peer->choked_upload)
281 active_peers.insert(remote_peer);
283 active_peers.erase(remote_peer);
286 void Peer::handleMessage()
288 constexpr std::array<const char*, 10> type_names{{"HANDSHAKE", "CHOKE", "UNCHOKE", "INTERESTED", "NOTINTERESTED",
289 "HAVE", "BITFIELD", "REQUEST", "PIECE", "CANCEL"}};
291 XBT_DEBUG("Received a %s message from %s", type_names[message->type], message->return_mailbox->get_cname());
293 auto known_peer = connected_peers.find(message->peer_id);
294 Connection* remote_peer = (known_peer == connected_peers.end()) ? nullptr : &known_peer->second;
295 xbt_assert(remote_peer != nullptr || message->type == MESSAGE_HANDSHAKE,
296 "The impossible did happened: A not-in-our-list peer sent us a message.");
298 switch (message->type) {
299 case MESSAGE_HANDSHAKE:
300 // Check if the peer is in our connection list.
301 if (remote_peer == nullptr) {
302 XBT_DEBUG("This peer %d was unknown, answer to its handshake", message->peer_id);
303 connected_peers.emplace(message->peer_id, Connection(message->peer_id));
304 sendMessage(message->return_mailbox, MESSAGE_HANDSHAKE, MESSAGE_HANDSHAKE_SIZE);
306 // Send our bitfield to the peer
307 sendBitfield(message->return_mailbox);
309 case MESSAGE_BITFIELD:
310 // Update the pieces list
311 updatePiecesCountFromBitfield(message->bitfield);
312 // Store the bitfield
313 remote_peer->bitfield = message->bitfield;
314 xbt_assert(not remote_peer->am_interested, "Should not be interested at first");
315 if (isInterestedBy(remote_peer)) {
316 remote_peer->am_interested = true;
317 sendMessage(message->return_mailbox, MESSAGE_INTERESTED, MESSAGE_INTERESTED_SIZE);
320 case MESSAGE_INTERESTED:
321 // Update the interested state of the peer.
322 remote_peer->interested = true;
323 updateActivePeersSet(remote_peer);
325 case MESSAGE_NOTINTERESTED:
326 remote_peer->interested = false;
327 updateActivePeersSet(remote_peer);
329 case MESSAGE_UNCHOKE:
330 xbt_assert(remote_peer->choked_download);
331 remote_peer->choked_download = false;
332 // Send requests to the peer, since it has unchoked us
333 if (remote_peer->am_interested)
334 requestNewPieceTo(remote_peer);
337 xbt_assert(not remote_peer->choked_download);
338 remote_peer->choked_download = true;
339 if (remote_peer->current_piece != -1)
340 removeCurrentPiece(remote_peer, remote_peer->current_piece);
343 XBT_DEBUG("\t for piece %d", message->piece);
344 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
345 "Wrong HAVE message received");
346 remote_peer->bitfield = remote_peer->bitfield | (1U << static_cast<unsigned int>(message->piece));
347 pieces_count[message->piece]++;
348 // If the piece is in our pieces, we tell the peer that we are interested.
349 if (not remote_peer->am_interested && hasNotPiece(message->piece)) {
350 remote_peer->am_interested = true;
351 sendMessage(message->return_mailbox, MESSAGE_INTERESTED, MESSAGE_INTERESTED_SIZE);
352 if (not remote_peer->choked_download)
353 requestNewPieceTo(remote_peer);
356 case MESSAGE_REQUEST:
357 xbt_assert(remote_peer->interested);
358 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
359 "Wrong HAVE message received");
360 if (not remote_peer->choked_upload) {
361 XBT_DEBUG("\t for piece %d (%d,%d)", message->piece, message->block_index,
362 message->block_index + message->block_length);
363 if (not hasNotPiece(message->piece)) {
364 sendPiece(message->return_mailbox, message->piece, message->block_index, message->block_length);
367 XBT_DEBUG("\t for piece %d but he is choked.", message->peer_id);
371 XBT_DEBUG(" \t for piece %d (%d,%d)", message->piece, message->block_index,
372 message->block_index + message->block_length);
373 xbt_assert(not remote_peer->choked_download);
374 xbt_assert(not remote_peer->choked_download, "Can't received a piece if I'm choked !");
375 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
376 "Wrong piece received");
377 // TODO: Execute a computation.
378 if (hasNotPiece(static_cast<unsigned int>(message->piece))) {
379 updateBitfieldBlocks(message->piece, message->block_index, message->block_length);
380 if (hasCompletedPiece(static_cast<unsigned int>(message->piece))) {
381 // Removing the piece from our piece list
382 removeCurrentPiece(remote_peer, message->piece);
383 // Setting the fact that we have the piece
384 bitfield_ = bitfield_ | (1U << static_cast<unsigned int>(message->piece));
385 XBT_DEBUG("My status is now %s", getStatus().c_str());
386 // Sending the information to all the peers we are connected to
387 sendHaveToAllPeers(message->piece);
388 // sending UNINTERESTED to peers that do not have what we want.
389 updateInterestedAfterReceive();
390 } else { // piece not completed
391 sendRequestTo(remote_peer, message->piece); // ask for the next block
394 XBT_DEBUG("However, we already have it");
395 requestNewPieceTo(remote_peer);
403 // Update the peer speed.
405 remote_peer->addSpeedValue(1.0 / (simgrid::s4u::Engine::get_clock() - begin_receive_time));
407 begin_receive_time = simgrid::s4u::Engine::get_clock();
410 /** Selects the appropriate piece to download and requests it to the remote_peer */
411 void Peer::requestNewPieceTo(Connection* remote_peer)
413 int piece = selectPieceToDownload(remote_peer);
415 current_pieces |= (1U << (unsigned int)piece);
416 sendRequestTo(remote_peer, piece);
420 void Peer::removeCurrentPiece(Connection* remote_peer, unsigned int current_piece)
422 current_pieces &= ~(1U << current_piece);
423 remote_peer->current_piece = -1;
426 /** @brief Return the piece to be downloaded
427 * There are two cases (as described in "Bittorrent Architecture Protocol", Ryan Toole :
428 * If a piece is partially downloaded, this piece will be selected prioritarily
429 * If the peer has strictly less than 4 pieces, he chooses a piece at random.
430 * If the peer has more than pieces, he downloads the pieces that are the less replicated (rarest policy).
431 * If all pieces have been downloaded or requested, we select a random requested piece (endgame mode).
432 * @param remote_peer: information about the connection
433 * @return the piece to download if possible. -1 otherwise
435 int Peer::selectPieceToDownload(const Connection* remote_peer)
437 int piece = partiallyDownloadedPiece(remote_peer);
438 // strict priority policy
443 if (countPieces(current_pieces) >= (FILE_PIECES - countPieces(bitfield_)) && isInterestedBy(remote_peer)) {
444 int nb_interesting_pieces = 0;
445 // compute the number of interesting pieces
446 for (unsigned int i = 0; i < FILE_PIECES; i++)
447 if (remotePeerHasMissingPiece(remote_peer, i))
448 nb_interesting_pieces++;
450 xbt_assert(nb_interesting_pieces != 0);
451 // get a random interesting piece
452 int random_piece_index = random.uniform_int(0, nb_interesting_pieces - 1);
453 int current_index = 0;
454 for (unsigned int i = 0; i < FILE_PIECES; i++) {
455 if (remotePeerHasMissingPiece(remote_peer, i)) {
456 if (random_piece_index == current_index) {
463 xbt_assert(piece != -1);
466 // Random first policy
467 if (countPieces(bitfield_) < 4 && isInterestedByFree(remote_peer)) {
468 int nb_interesting_pieces = 0;
469 // compute the number of interesting pieces
470 for (unsigned int i = 0; i < FILE_PIECES; i++)
471 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
472 nb_interesting_pieces++;
473 xbt_assert(nb_interesting_pieces != 0);
474 // get a random interesting piece
475 int random_piece_index = random.uniform_int(0, nb_interesting_pieces - 1);
476 int current_index = 0;
477 for (unsigned int i = 0; i < FILE_PIECES; i++) {
478 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i)) {
479 if (random_piece_index == current_index) {
486 xbt_assert(piece != -1);
488 } else { // Rarest first policy
489 short min = SHRT_MAX;
490 int nb_min_pieces = 0;
491 int current_index = 0;
492 // compute the smallest number of copies of available pieces
493 for (unsigned int i = 0; i < FILE_PIECES; i++) {
494 if (pieces_count[i] < min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
495 min = pieces_count[i];
498 xbt_assert(min != SHRT_MAX || not isInterestedByFree(remote_peer));
499 // compute the number of rarest pieces
500 for (unsigned int i = 0; i < FILE_PIECES; i++)
501 if (pieces_count[i] == min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
504 xbt_assert(nb_min_pieces != 0 || not isInterestedByFree(remote_peer));
505 // get a random rarest piece
506 int random_rarest_index = 0;
507 if (nb_min_pieces > 0) {
508 random_rarest_index = random.uniform_int(0, nb_min_pieces - 1);
510 for (unsigned int i = 0; i < FILE_PIECES; i++)
511 if (pieces_count[i] == min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i)) {
512 if (random_rarest_index == current_index) {
519 xbt_assert(piece != -1 || not isInterestedByFree(remote_peer));
524 void Peer::updateChokedPeers()
526 if (nbInterestedPeers() == 0)
528 XBT_DEBUG("(%d) update_choked peers %zu active peers", id, active_peers.size());
529 // update the current round
530 round_ = (round_ + 1) % 3;
531 Connection* chosen_peer = nullptr;
532 // select first active peer and remove it from the set
533 Connection* choked_peer;
534 if (active_peers.empty()) {
535 choked_peer = nullptr;
537 choked_peer = *active_peers.begin();
538 active_peers.erase(choked_peer);
541 /**If we are currently seeding, we unchoke the peer which has been unchoked the last time.*/
543 double unchoke_time = simgrid::s4u::Engine::get_clock() + 1;
544 for (auto& kv : connected_peers) {
545 Connection& remote_peer = kv.second;
546 if (remote_peer.last_unchoke < unchoke_time && remote_peer.interested && remote_peer.choked_upload) {
547 unchoke_time = remote_peer.last_unchoke;
548 chosen_peer = &remote_peer;
552 // Random optimistic unchoking
556 // We choose a random peer to unchoke.
557 auto chosen_peer_it = connected_peers.begin();
558 std::advance(chosen_peer_it, random.uniform_int(0, static_cast<int>(connected_peers.size() - 1)));
559 chosen_peer = &chosen_peer_it->second;
560 if (not chosen_peer->interested || not chosen_peer->choked_upload)
561 chosen_peer = nullptr;
563 XBT_DEBUG("Nothing to do, keep going");
565 } while (chosen_peer == nullptr && j < MAXIMUM_PEERS);
567 // Use the "fastest download" policy.
568 double fastest_speed = 0.0;
569 for (auto& kv : connected_peers) {
570 Connection& remote_peer = kv.second;
571 if (remote_peer.peer_speed > fastest_speed && remote_peer.choked_upload && remote_peer.interested) {
572 fastest_speed = remote_peer.peer_speed;
573 chosen_peer = &remote_peer;
579 if (chosen_peer != nullptr)
580 XBT_DEBUG("(%d) update_choked peers unchoked (%d) ; int (%d) ; choked (%d) ", id, chosen_peer->id,
581 chosen_peer->interested, chosen_peer->choked_upload);
583 if (choked_peer != chosen_peer) {
584 if (choked_peer != nullptr) {
585 xbt_assert(not choked_peer->choked_upload, "Tries to choked a choked peer");
586 choked_peer->choked_upload = true;
587 updateActivePeersSet(choked_peer);
588 XBT_DEBUG("(%d) Sending a CHOKE to %d", id, choked_peer->id);
589 sendMessage(choked_peer->mailbox_, MESSAGE_CHOKE, MESSAGE_CHOKE_SIZE);
591 if (chosen_peer != nullptr) {
592 xbt_assert((chosen_peer->choked_upload), "Tries to unchoked an unchoked peer");
593 chosen_peer->choked_upload = false;
594 active_peers.insert(chosen_peer);
595 chosen_peer->last_unchoke = simgrid::s4u::Engine::get_clock();
596 XBT_DEBUG("(%d) Sending a UNCHOKE to %d", id, chosen_peer->id);
597 updateActivePeersSet(chosen_peer);
598 sendMessage(chosen_peer->mailbox_, MESSAGE_UNCHOKE, MESSAGE_UNCHOKE_SIZE);
603 /** @brief Update "interested" state of peers: send "not interested" to peers that don't have any more pieces we want.*/
604 void Peer::updateInterestedAfterReceive()
606 for (auto& kv : connected_peers) {
607 Connection& remote_peer = kv.second;
608 if (remote_peer.am_interested) {
609 bool interested = false;
610 // Check if the peer still has a piece we want.
611 for (unsigned int i = 0; i < FILE_PIECES; i++)
612 if (remotePeerHasMissingPiece(&remote_peer, i)) {
617 if (not interested) { // no more piece to download from connection
618 remote_peer.am_interested = false;
619 sendMessage(remote_peer.mailbox_, MESSAGE_NOTINTERESTED, MESSAGE_NOTINTERESTED_SIZE);
625 void Peer::updateBitfieldBlocks(int piece, int block_index, int block_length)
627 xbt_assert((piece >= 0 && static_cast<unsigned int>(piece) <= FILE_PIECES), "Wrong piece.");
628 xbt_assert((block_index >= 0 && static_cast<unsigned int>(block_index) <= PIECES_BLOCKS), "Wrong block : %d.",
630 for (int i = block_index; i < (block_index + block_length); i++)
631 bitfield_blocks |= (1ULL << static_cast<unsigned int>(piece * PIECES_BLOCKS + i));
634 bool Peer::hasCompletedPiece(unsigned int piece) const
636 for (unsigned int i = 0; i < PIECES_BLOCKS; i++)
637 if (not(bitfield_blocks & 1ULL << (piece * PIECES_BLOCKS + i)))
642 int Peer::getFirstMissingBlockFrom(int piece) const
644 for (unsigned int i = 0; i < PIECES_BLOCKS; i++)
645 if (not(bitfield_blocks & 1ULL << (piece * PIECES_BLOCKS + i)))
650 /** Returns a piece that is partially downloaded and stored by the remote peer if any -1 otherwise. */
651 int Peer::partiallyDownloadedPiece(const Connection* remote_peer) const
653 for (unsigned int i = 0; i < FILE_PIECES; i++)
654 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i) && getFirstMissingBlockFrom(i) > 0)