void request_new_piece_to_peer(peer_t peer, connection_t remote_peer);
void send_request_to_peer(peer_t peer, connection_t remote_peer, int piece);
-void remove_current_piece(peer_t peer, connection_t remote_peer,
- int current_piece);
+void remove_current_piece(peer_t peer, connection_t remote_peer, int current_piece);
/**
/**
* Return the piece to be downloaded
* There are two cases (as described in "Bittorrent Architecture Protocol", Ryan Toole :
+ * If a piece is partially downloaded, this piece will be selected prioritarily
* If the peer has strictly less than 4 pieces, he chooses a piece at random.
* If the peer has more than pieces, he downloads the pieces that are the less
- * replicated
- * Note: "end game mode" policy is not implemented
+ * replicated (rarest policy).
+ * If all pieces have been downloaded or requested, we select a random requested piece (endgame mode).
+
* @param peer: local peer
* @param remote_peer: information about the connection
* @return the piece to download if possible. -1 otherwise
*/
int select_piece_to_download(peer_t peer, connection_t remote_peer)
{
- // TODO : add strict priority policy
+ int piece = -1;
+
+ piece = partially_downloaded_piece(peer, remote_peer);
+ // strict priority policy
+ if (piece != -1)
+ return piece;
- if (xbt_dynar_length(peer->current_pieces) >= (FILE_PIECES - peer->pieces)) { // end game mode
- return -1;
+ // end game mode
+ if (xbt_dynar_length(peer->current_pieces) >= (FILE_PIECES - peer->pieces) && is_interested(peer, remote_peer)) {
+ int i;
+ int nb_interesting_pieces = 0;
+ int random_piece_index, current_index = 0;
+ // compute the number of interesting pieces
+ for (i = 0; i < FILE_PIECES; i++) {
+ if (peer->bitfield[i] == '0' && remote_peer->bitfield[i] == '1') {
+ nb_interesting_pieces++;
+ }
+ }
+ xbt_assert(nb_interesting_pieces != 0, "WTF !!!");
+ // get a random interesting piece
+ random_piece_index = RngStream_RandInt(peer->stream, 0, nb_interesting_pieces-1);
+ for (i = 0; i < FILE_PIECES; i++) {
+ if (peer->bitfield[i] == '0' && remote_peer->bitfield[i] == '1') {
+ if (random_piece_index == current_index) {
+ piece = i;
+ break;
+ }
+ current_index++;
+ }
+ }
+ xbt_assert(piece != -1,"WTF !!!");
+ return piece;
}
- if (peer->pieces < 4 && is_interested_and_free(peer, remote_peer)) { // Random first policy
- int piece = 0;
- do {
- piece = RngStream_RandInt(peer->stream, 0, FILE_PIECES - 1);;
- } while (!
- (peer->bitfield[piece] == '0'
- && remote_peer->bitfield[piece] == '1'
- && !in_current_pieces(peer, piece)));
+
+ // Random first policy
+ if (peer->pieces < 4 && is_interested_and_free(peer, remote_peer)) {
+ int i;
+ int nb_interesting_pieces = 0;
+ int random_piece_index, current_index = 0;
+ // compute the number of interesting pieces
+ for (i = 0; i < FILE_PIECES; i++) {
+ if (peer->bitfield[i] == '0' && remote_peer->bitfield[i] == '1' && !in_current_pieces(peer, i)) {
+ nb_interesting_pieces++;
+ }
+ }
+ xbt_assert(nb_interesting_pieces != 0, "WTF !!!");
+ // get a random interesting piece
+ random_piece_index = RngStream_RandInt(peer->stream, 0, nb_interesting_pieces-1);
+ for (i = 0; i < FILE_PIECES; i++) {
+ if (peer->bitfield[i] == '0' && remote_peer->bitfield[i] == '1' && !in_current_pieces(peer, i)) {
+ if (random_piece_index == current_index) {
+ piece = i;
+ break;
+ }
+ current_index++;
+ }
+ }
+ xbt_assert(piece != -1,"WTF !!!");
return piece;
} else { // Rarest first policy
- int i, min_piece = -1;
+ int i;
short min = SHRT_MAX;
+ int nb_min_pieces = 0;
+ int random_rarest_index, current_index = 0;
+ // compute the smallest number of copies of available pieces
for (i = 0; i < FILE_PIECES; i++) {
if (peer->pieces_count[i] < min && peer->bitfield[i] == '0'
- && remote_peer->bitfield[i] == '1' && !in_current_pieces(peer, i)) {
- min = peer->pieces_count[i];
- min_piece = i;
+ && remote_peer->bitfield[i] == '1' && !in_current_pieces(peer, i))
+ min = peer->pieces_count[i];
+ }
+ xbt_assert(min != SHRT_MAX || !is_interested_and_free(peer, remote_peer), "WTF !!!");
+ // compute the number of rarest pieces
+ for (i = 0; i < FILE_PIECES; i++) {
+ if (peer->pieces_count[i] == min && peer->bitfield[i] == '0'
+ && remote_peer->bitfield[i] == '1' && !in_current_pieces(peer, i))
+ nb_min_pieces++;
+ }
+ xbt_assert(nb_min_pieces != 0 || !is_interested_and_free(peer, remote_peer), "WTF !!!");
+ // get a random rarest piece
+ random_rarest_index = RngStream_RandInt(peer->stream, 0, nb_min_pieces-1);
+ for (i = 0; i < FILE_PIECES; i++) {
+ if (peer->pieces_count[i] == min && peer->bitfield[i] == '0'
+ && remote_peer->bitfield[i] == '1' && !in_current_pieces(peer, i)) {
+ if (random_rarest_index == current_index) {
+ piece = i;
+ break;
+ }
+ current_index++;
}
}
- // TODO: add randomness when selecting a rarest piece
- return min_piece;
+ xbt_assert(piece != -1 || !is_interested_and_free(peer, remote_peer),"WTF !!!");
+ return piece;
}
}
}
/**
- * Returns a piece that is stored by the remote peer but not by the local peer.
- * -1 otherwise.
+ * Indicates if the remote peer has a piece not stored by the local peer
*/
int is_interested(peer_t peer, connection_t remote_peer)
{
return 0;
}
+/**
+ * Indicates if the remote peer has a piece not stored by the local peer nor requested by the local peer
+ */
int is_interested_and_free(peer_t peer, connection_t remote_peer)
{
xbt_assert(remote_peer->bitfield, "Bitfield not received");
int i;
for (i = 0; i < FILE_PIECES; i++) {
if (remote_peer->bitfield[i] == '1' && peer->bitfield[i] == '0'
- && !in_current_pieces(peer, i)) {
+ && !in_current_pieces(peer, i)) {
if (get_first_block(peer, i) > 0)
- return i;
+ return i;
}
}
return -1;