sendrecv.cpp

   1 /*
   2  *  sendrecv.cpp
   3  *  most of the swift's state machine
   4  *
   5  *  Created by Victor Grishchenko on 3/6/09.
   6  *  Copyright 2009 Delft University of Technology. All rights reserved.
   7  *
   8  */
   9 #include "swift.h"
  10 #include <algorithm>  // kill it
  11
  12 using namespace swift;
  13 using namespace std;
  14
  15 /*
  16  TODO  25 Oct 18:55
  17  - range: ALL
  18  - randomized testing of advanced ops (new testcase)
  19  */
  20
  21 void    Channel::AddPeakHashes (Datagram& dgram) {
  22     for(int i=0; i<file().peak_count(); i++) {
  23         bin64_t peak = file().peak(i);
  24         dgram.Push8(SWIFT_HASH);
  25         dgram.Push32((uint32_t)peak);
  26         dgram.PushHash(file().peak_hash(i));
  27         //DLOG(INFO)<<"#"<<id<<" +pHASH"<<file().peak(i);
  28         dprintf("%s #%u +phash %s\n",tintstr(),id_,peak.str());
  29     }
  30 }
  31
  32
  33 void    Channel::AddUncleHashes (Datagram& dgram, bin64_t pos) {
  34     bin64_t peak = file().peak_for(pos);
  35     while (pos!=peak && ((NOW&3)==3 || !data_out_cap_.within(pos.parent())) &&
  36             ack_in_.get(pos.parent())==binmap_t::EMPTY  ) {
  37         bin64_t uncle = pos.sibling();
  38         dgram.Push8(SWIFT_HASH);
  39         dgram.Push32((uint32_t)uncle);
  40         dgram.PushHash( file().hash(uncle) );
  41         //DLOG(INFO)<<"#"<<id<<" +uHASH"<<uncle;
  42         dprintf("%s #%u +hash %s\n",tintstr(),id_,uncle.str());
  43         pos = pos.parent();
  44     }
  45 }
  46
  47
  48 bin64_t           Channel::ImposeHint () {
  49     uint64_t twist = peer_channel_id_;  // got no hints, send something randomly
  50     twist &= file().peak(0); // FIXME may make it semi-seq here
  51     file().ack_out().twist(twist);
  52     ack_in_.twist(twist);
  53     bin64_t my_pick =
  54         file().ack_out().find_filtered(ack_in_,bin64_t::ALL,binmap_t::FILLED);
  55     while (my_pick.width()>max(1,(int)cwnd_))
  56         my_pick = my_pick.left();
  57     file().ack_out().twist(0);
  58     ack_in_.twist(0);
  59     return my_pick.twisted(twist);
  60 }
  61
  62
  63 bin64_t        Channel::DequeueHint () {
  64     if (hint_in_.empty() && last_recv_time_>NOW-rtt_avg_-TINT_SEC) {
  65         bin64_t my_pick = ImposeHint(); // FIXME move to the loop
  66         if (my_pick!=bin64_t::NONE) {
  67             hint_in_.push_back(my_pick);
  68             dprintf("%s #%u *hint %s\n",tintstr(),id_,my_pick.str());
  69         }
  70     }
  71     bin64_t send = bin64_t::NONE;
  72     while (!hint_in_.empty() && send==bin64_t::NONE) {
  73         bin64_t hint = hint_in_.front().bin;
  74         tint time = hint_in_.front().time;
  75         hint_in_.pop_front();
  76         while (!hint.is_base()) { // FIXME optimize; possible attack
  77             hint_in_.push_front(tintbin(time,hint.right()));
  78             hint = hint.left();
  79         }
  80         //if (time < NOW-TINT_SEC*3/2 )
  81         //    continue;  bad idea
  82         if (ack_in_.get(hint)!=binmap_t::FILLED)
  83             send = hint;
  84     }
  85     uint64_t mass = 0;
  86     for(int i=0; i<hint_in_.size(); i++)
  87         mass += hint_in_[i].bin.width();
  88     dprintf("%s #%u dequeued %s [%lli]\n",tintstr(),id_,send.str(),mass);
  89     return send;
  90 }
  91
  92
  93 void    Channel::AddHandshake (Datagram& dgram) {
  94     if (!peer_channel_id_) { // initiating
  95         dgram.Push8(SWIFT_HASH);
  96         dgram.Push32(bin64_t::ALL32);
  97         dgram.PushHash(file().root_hash());
  98         dprintf("%s #%u +hash ALL %s\n",
  99                 tintstr(),id_,file().root_hash().hex().c_str());
 100     }
 101     dgram.Push8(SWIFT_HANDSHAKE);
 102     int encoded = EncodeID(id_);
 103     dgram.Push32(encoded);
 104     dprintf("%s #%u +hs %x\n",tintstr(),id_,encoded);
 105     have_out_.clear();
 106     AddHave(dgram);
 107 }
 108
 109
 110 void    Channel::Send () {
 111     Datagram dgram(socket_,peer());
 112     dgram.Push32(peer_channel_id_);
 113     bin64_t data = bin64_t::NONE;
 114     if ( is_established() ) {
 115         // FIXME: seeder check
 116         AddAck(dgram);
 117         if (!file().is_complete())
 118             AddHint(dgram);
 119         AddPex(dgram);
 120         TimeoutDataOut();
 121         data = AddData(dgram);
 122     } else {
 123         AddHandshake(dgram);
 124         AddAck(dgram);
 125     }
 126     dprintf("%s #%u sent %ib %s:%x\n",
 127             tintstr(),id_,dgram.size(),peer().str(),peer_channel_id_);
 128     if (dgram.size()==4) {// only the channel id; bare keep-alive
 129         data = bin64_t::ALL;
 130     }
 131     if (dgram.Send()==-1)
 132         print_error("can't send datagram");
 133     last_send_time_ = NOW;
 134     sent_since_recv_++;
 135     dgrams_sent_++;
 136 }
 137
 138
 139 void    Channel::AddHint (Datagram& dgram) {
 140
 141     tint plan_for = max(TINT_SEC,rtt_avg_*4);
 142
 143     tint timed_out = NOW - plan_for*2;
 144     while ( !hint_out_.empty() && hint_out_.front().time < timed_out ) {
 145         hint_out_size_ -= hint_out_.front().bin.width();
 146         hint_out_.pop_front();
 147     }
 148
 149     int plan_pck = max ( (tint)1, plan_for / dip_avg_ );
 150
 151     if ( hint_out_size_ < plan_pck ) {
 152
 153         int diff = plan_pck - hint_out_size_; // TODO: aggregate
 154         bin64_t hint = transfer().picker().Pick(ack_in_,diff,NOW+plan_for*2);
 155
 156         if (hint!=bin64_t::NONE) {
 157             dgram.Push8(SWIFT_HINT);
 158             dgram.Push32(hint);
 159             dprintf("%s #%u +hint %s [%lli]\n",tintstr(),id_,hint.str(),hint_out_size_);
 160             hint_out_.push_back(hint);
 161             hint_out_size_ += hint.width();
 162         } else
 163             dprintf("%s #%u Xhint\n",tintstr(),id_);
 164
 165     }
 166 }
 167
 168
 169 bin64_t        Channel::AddData (Datagram& dgram) {
 170
 171     if (!file().size()) // know nothing
 172         return bin64_t::NONE;
 173
 174     bin64_t tosend = bin64_t::NONE;
 175     tint luft = send_interval_>>4; // may wake up a bit earlier
 176     if (data_out_.size()<cwnd_ &&
 177             last_data_out_time_+send_interval_<=NOW+luft) {
 178         tosend = DequeueHint();
 179         if (tosend==bin64_t::NONE) {
 180             dprintf("%s #%u sendctrl no idea what to send\n",tintstr(),id_);
 181             if (send_control_!=KEEP_ALIVE_CONTROL)
 182                 SwitchSendControl(KEEP_ALIVE_CONTROL);
 183         }
 184     } else
 185         dprintf("%s #%u sendctrl wait cwnd %f data_out %i next %s\n",
 186                 tintstr(),id_,cwnd_,data_out_.size(),tintstr(last_data_out_time_+NOW-send_interval_));
 187
 188     if (tosend==bin64_t::NONE)// && (last_data_out_time_>NOW-TINT_SEC || data_out_.empty()))
 189         return bin64_t::NONE; // once in a while, empty data is sent just to check rtt FIXED
 190
 191     if (ack_in_.is_empty() && file().size())
 192         AddPeakHashes(dgram);
 193     AddUncleHashes(dgram,tosend);
 194     if (!ack_in_.is_empty()) // TODO: cwnd_>1
 195         data_out_cap_ = tosend;
 196
 197     if (dgram.size()>254) {
 198         dgram.Send(); // kind of fragmentation
 199         dgram.Push32(peer_channel_id_);
 200     }
 201
 202     dgram.Push8(SWIFT_DATA);
 203     dgram.Push32(tosend.to32());
 204
 205     uint8_t buf[1024];
 206     size_t r = pread(file().file_descriptor(),buf,1024,tosend.base_offset()<<10);
 207     // TODO: corrupted data, retries, caching
 208     if (r<0) {
 209         print_error("error on reading");
 210         return bin64_t::NONE;
 211     }
 212     assert(dgram.space()>=r+4+1);
 213     dgram.Push(buf,r);
 214
 215     last_data_out_time_ = NOW;
 216     data_out_.push_back(tosend);
 217     dprintf("%s #%u +data %s\n",tintstr(),id_,tosend.str());
 218
 219     return tosend;
 220 }
 221
 222
 223 void    Channel::AddAck (Datagram& dgram) {
 224     if (data_in_==tintbin())
 225         return;
 226     dgram.Push8(SWIFT_ACK);
 227     dgram.Push32(data_in_.bin.to32()); // FIXME not cover
 228     dgram.Push64(data_in_.time); // FIXME 32
 229     have_out_.set(data_in_.bin);
 230     dprintf("%s #%u +ack %s %s\n",
 231         tintstr(),id_,data_in_.bin.str(),tintstr(data_in_.time));
 232     if (data_in_.bin.layer()>2)
 233         data_in_dbl_ = data_in_.bin;
 234     data_in_ = tintbin();
 235 }
 236
 237
 238 void    Channel::AddHave (Datagram& dgram) {
 239     if (data_in_dbl_!=bin64_t::NONE) { // TODO: do redundancy better
 240         dgram.Push8(SWIFT_HAVE);
 241         dgram.Push32(data_in_dbl_.to32());
 242         data_in_dbl_=bin64_t::NONE;
 243     }
 244     for(int count=0; count<4; count++) {
 245         bin64_t ack = file().ack_out().find_filtered // FIXME: do rotating queue
 246             (have_out_, bin64_t::ALL, binmap_t::FILLED);
 247         if (ack==bin64_t::NONE)
 248             break;
 249         ack = file().ack_out().cover(ack);
 250         have_out_.set(ack);
 251         dgram.Push8(SWIFT_HAVE);
 252         dgram.Push32(ack.to32());
 253         dprintf("%s #%u +have %s\n",tintstr(),id_,ack.str());
 254     }
 255 }
 256
 257
 258 void    Channel::Recv (Datagram& dgram) {
 259     dprintf("%s #%u recvd %ib\n",tintstr(),id_,dgram.size()+4);
 260     dgrams_rcvd_++;
 261     if (last_send_time_ && rtt_avg_==TINT_SEC && dev_avg_==0) {
 262         rtt_avg_ = NOW - last_send_time_;
 263         dev_avg_ = rtt_avg_;
 264         dip_avg_ = rtt_avg_;
 265         dprintf("%s #%u sendctrl rtt init %lli\n",tintstr(),id_,rtt_avg_);
 266     }
 267     bin64_t data = dgram.size() ? bin64_t::NONE : bin64_t::ALL;
 268     while (dgram.size()) {
 269         uint8_t type = dgram.Pull8();
 270         switch (type) {
 271             case SWIFT_HANDSHAKE: OnHandshake(dgram); break;
 272             case SWIFT_DATA:      data=OnData(dgram); break;
 273             case SWIFT_HAVE:      OnHave(dgram); break;
 274             case SWIFT_ACK:       OnAck(dgram); break;
 275             case SWIFT_HASH:      OnHash(dgram); break;
 276             case SWIFT_HINT:      OnHint(dgram); break;
 277             case SWIFT_PEX_ADD:   OnPex(dgram); break;
 278             default:
 279                 eprintf("%s #%u ?msg id unknown %i\n",tintstr(),id_,(int)type);
 280                 return;
 281         }
 282     }
 283     last_recv_time_ = NOW;
 284     sent_since_recv_ = 0;
 285 }
 286
 287
 288 void    Channel::OnHash (Datagram& dgram) {
 289     bin64_t pos = dgram.Pull32();
 290     Sha1Hash hash = dgram.PullHash();
 291     file().OfferHash(pos,hash);
 292     dprintf("%s #%u -hash %s\n",tintstr(),id_,pos.str());
 293 }
 294
 295
 296 void    Channel::CleanHintOut (bin64_t pos) {
 297     int hi = 0;
 298     while (hi<hint_out_.size() && !pos.within(hint_out_[hi].bin))
 299         hi++;
 300     if (hi==hint_out_.size())
 301         return; // something not hinted or hinted in far past
 302     while (hi--) { // removing likely snubbed hints
 303         hint_out_size_ -= hint_out_.front().bin.width();
 304         hint_out_.pop_front();
 305     }
 306     while (hint_out_.front().bin!=pos) {
 307         tintbin f = hint_out_.front();
 308         f.bin = f.bin.towards(pos);
 309         hint_out_.front().bin = f.bin.sibling();
 310         hint_out_.push_front(f);
 311     }
 312     hint_out_.pop_front();
 313     hint_out_size_--;
 314 }
 315
 316
 317 bin64_t Channel::OnData (Datagram& dgram) {  // TODO: HAVE NONE for corrupted data
 318     bin64_t pos = dgram.Pull32();
 319     uint8_t *data;
 320     int length = dgram.Pull(&data,1024);
 321     bool ok = (pos==bin64_t::NONE) || file().OfferData(pos, (char*)data, length) ;
 322     dprintf("%s #%u %cdata %s\n",tintstr(),id_,ok?'-':'!',pos.str());
 323     data_in_ = tintbin(NOW,bin64_t::NONE);
 324     if (!ok)
 325         return bin64_t::NONE;
 326     data_in_.bin = pos;
 327     if (pos!=bin64_t::NONE) {
 328         if (last_data_in_time_) {
 329             tint dip = NOW - last_data_in_time_;
 330             dip_avg_ = ( dip_avg_*3 + dip ) >> 2;
 331         }
 332         last_data_in_time_ = NOW;
 333     }
 334     CleanHintOut(pos);
 335     return pos;
 336 }
 337
 338
 339 void    Channel::OnAck (Datagram& dgram) {
 340     bin64_t ackd_pos = dgram.Pull32();
 341     tint peer_time_ = dgram.Pull64(); // FIXME 32
 342     // FIXME FIXME: wrap around here
 343     if (ackd_pos==bin64_t::NONE)
 344         return; // likely, brocken packet / insufficient hashes
 345     if (file().size() && ackd_pos.base_offset()>=file().packet_size()) {
 346         eprintf("invalid ack: %s\n",ackd_pos.str());
 347         return;
 348     }
 349     ack_in_.set(ackd_pos);
 350     int di = 0, ri = 0;
 351     // find an entry for the send (data out) event
 352     while (  di<data_out_.size() && ( data_out_[di]==tintbin() ||
 353            !data_out_[di].bin.within(ackd_pos) )  )
 354         di++;
 355     // FUTURE: delayed acks
 356     // rule out retransmits
 357     while (  ri<data_out_tmo_.size() && !data_out_tmo_[ri].bin.within(ackd_pos) )
 358         ri++;
 359     dprintf("%s #%u %cack %s %lli\n",tintstr(),id_,
 360             di==data_out_.size()?'?':'-',ackd_pos.str(),peer_time_);
 361     if (di!=data_out_.size() && ri==data_out_tmo_.size()) { // not a retransmit
 362             // round trip time calculations
 363         tint rtt = NOW-data_out_[di].time;
 364         rtt_avg_ = (rtt_avg_*7 + rtt) >> 3;
 365         dev_avg_ = ( dev_avg_*3 + abs(rtt-rtt_avg_) ) >> 2;
 366         assert(data_out_[di].time!=TINT_NEVER);
 367             // one-way delay calculations
 368         tint owd = peer_time_ - data_out_[di].time;
 369         owd_cur_bin_ = (owd_cur_bin_+1) & 3;
 370         owd_current_[owd_cur_bin_] = owd;
 371         if ( owd_min_bin_start_+TINT_SEC*30 < NOW ) {
 372             owd_min_bin_start_ = NOW;
 373             owd_min_bin_ = (owd_min_bin_+1) & 3;
 374             owd_min_bins_[owd_min_bin_] = TINT_NEVER;
 375         }
 376         if (owd_min_bins_[owd_min_bin_]>owd)
 377             owd_min_bins_[owd_min_bin_] = owd;
 378         dprintf("%s #%u sendctrl rtt %lli dev %lli based on %s\n",
 379                 tintstr(),id_,rtt_avg_,dev_avg_,data_out_[di].bin.str());
 380         ack_rcvd_recent_++;
 381         data_out_[di]=tintbin();
 382     }
 383     // early loss detection by packet reordering
 384     for (int re=0; re<di-MAX_REORDERING; re++) {
 385         if (data_out_[re]==tintbin())
 386             continue;
 387         ack_not_rcvd_recent_++;
 388         data_out_tmo_.push_back(data_out_.front().bin);
 389         dprintf("%s #%u Rdata %s\n",tintstr(),id_,data_out_.front().bin.str());
 390         data_out_cap_ = bin64_t::ALL;
 391         data_out_[re] = tintbin();
 392     }
 393     // clear zeroed items
 394     while (!data_out_.empty() && ( data_out_.front()==tintbin() ||
 395             ack_in_.is_filled(data_out_.front().bin) ) )
 396         data_out_.pop_front();
 397     assert(data_out_.empty() || data_out_.front().time!=TINT_NEVER);
 398 }
 399
 400
 401 void Channel::TimeoutDataOut ( ) {
 402     // losses: timeouted packets
 403     tint timeout = NOW - ack_timeout();
 404     while (!data_out_.empty() &&
 405         ( data_out_.front().time<timeout || data_out_.front()==tintbin() ) ) {
 406         if (data_out_.front()!=tintbin() && ack_in_.is_empty(data_out_.front().bin)) {
 407             ack_not_rcvd_recent_++;
 408             data_out_cap_ = bin64_t::ALL;
 409             data_out_tmo_.push_back(data_out_.front().bin);
 410             dprintf("%s #%u Tdata %s\n",tintstr(),id_,data_out_.front().bin.str());
 411         }
 412         data_out_.pop_front();
 413     }
 414     // clear retransmit queue of older items
 415     while (!data_out_tmo_.empty() && data_out_tmo_.front().time<NOW-MAX_POSSIBLE_RTT)
 416         data_out_tmo_.pop_front();
 417 }
 418
 419
 420 void Channel::OnHave (Datagram& dgram) {
 421     bin64_t ackd_pos = dgram.Pull32();
 422     if (ackd_pos==bin64_t::NONE)
 423         return; // wow, peer has hashes
 424     ack_in_.set(ackd_pos);
 425     dprintf("%s #%u -have %s\n",tintstr(),id_,ackd_pos.str());
 426 }
 427
 428
 429 void    Channel::OnHint (Datagram& dgram) {
 430     bin64_t hint = dgram.Pull32();
 431     // FIXME: wake up here
 432     hint_in_.push_back(hint);
 433     dprintf("%s #%u -hint %s\n",tintstr(),id_,hint.str());
 434 }
 435
 436
 437 void Channel::OnHandshake (Datagram& dgram) {
 438     peer_channel_id_ = dgram.Pull32();
 439     dprintf("%s #%u -hs %x\n",tintstr(),id_,peer_channel_id_);
 440     // self-connection check
 441     if (!SELF_CONN_OK) {
 442         uint32_t try_id = DecodeID(peer_channel_id_);
 443         if (channel(try_id) && !channel(try_id)->peer_channel_id_) {
 444             peer_channel_id_ = 0;
 445             Close();
 446             return; // this is a self-connection
 447         }
 448     }
 449     // FUTURE: channel forking
 450 }
 451
 452
 453 void Channel::OnPex (Datagram& dgram) {
 454     uint32_t ipv4 = dgram.Pull32();
 455     uint16_t port = dgram.Pull16();
 456     Address addr(ipv4,port);
 457     dprintf("%s #%u -pex %s\n",tintstr(),id_,addr.str());
 458     transfer().OnPexIn(addr);
 459 }
 460
 461
 462 void    Channel::AddPex (Datagram& dgram) {
 463     int chid = transfer().RevealChannel(pex_out_);
 464     if (chid==-1 || chid==id_)
 465         return;
 466     Address a = channels[chid]->peer();
 467     dgram.Push8(SWIFT_PEX_ADD);
 468     dgram.Push32(a.ipv4());
 469     dgram.Push16(a.port());
 470     dprintf("%s #%u +pex %s\n",tintstr(),id_,a.str());
 471 }
 472
 473
 474 Channel*    Channel::RecvDatagram (int socket) {
 475     Datagram data(socket);
 476     data.Recv();
 477     const Address& addr = data.address();
 478 #define return_log(...) { printf(__VA_ARGS__); return NULL; }
 479     if (data.size()<4)
 480         return_log("datagram shorter than 4 bytes %s\n",addr.str());
 481     uint32_t mych = data.Pull32();
 482     Sha1Hash hash;
 483     Channel* channel = NULL;
 484     if (!mych) { // handshake initiated
 485         if (data.size()<1+4+1+4+Sha1Hash::SIZE)
 486             return_log ("%s #0 incorrect size %i initial handshake packet %s\n",
 487                         tintstr(),data.size(),addr.str());
 488         uint8_t hashid = data.Pull8();
 489         if (hashid!=SWIFT_HASH)
 490             return_log ("%s #0 no hash in the initial handshake %s\n",
 491                         tintstr(),addr.str());
 492         bin64_t pos = data.Pull32();
 493         if (pos!=bin64_t::ALL)
 494             return_log ("%s #0 that is not the root hash %s\n",tintstr(),addr.str());
 495         hash = data.PullHash();
 496         FileTransfer* file = FileTransfer::Find(hash);
 497         if (!file)
 498             return_log ("%s #0 hash %s unknown, no such file %s\n",tintstr(),hash.hex().c_str(),addr.str());
 499         dprintf("%s #0 -hash ALL %s\n",tintstr(),hash.hex().c_str());
 500         for(binqueue::iterator i=file->hs_in_.begin(); i!=file->hs_in_.end(); i++)
 501             if (channels[*i] && channels[*i]->peer_==data.address() &&
 502                 channels[*i]->last_recv_time_>NOW-TINT_SEC*2)
 503                 return_log("%s #0 have a channel already to %s\n",tintstr(),addr.str());
 504         channel = new Channel(file, socket, data.address());
 505     } else {
 506         mych = DecodeID(mych);
 507         if (mych>=channels.size())
 508             return_log("%s invalid channel #%u, %s\n",tintstr(),mych,addr.str());
 509         channel = channels[mych];
 510         if (!channel)
 511             return_log ("%s #%u is already closed\n",tintstr(),mych,addr.str());
 512         if (channel->peer() != addr)
 513             return_log ("%s #%u invalid peer address %s!=%s\n",
 514                         tintstr(),mych,channel->peer().str(),addr.str());
 515         channel->own_id_mentioned_ = true;
 516     }
 517     //dprintf("recvd %i bytes for %i\n",data.size(),channel->id);
 518     channel->Recv(data);
 519     return channel;
 520 }
 521
 522
 523 void    Channel::Loop (tint howlong) {
 524
 525     tint limit = Datagram::Time() + howlong;
 526
 527     do {
 528
 529         tint send_time(TINT_NEVER);
 530         Channel* sender(NULL);
 531         while (!sender && !send_queue.is_empty()) { // dequeue
 532             tintbin next = send_queue.pop();
 533             sender = channel((int)next.bin);
 534             send_time = next.time;
 535             if (sender && sender->next_send_time_!=send_time &&
 536                      sender->next_send_time_!=TINT_NEVER )
 537                 sender = NULL; // it was a stale entry
 538         }
 539
 540         if ( sender!=NULL && send_time<=NOW ) { // it's time
 541
 542             dprintf("%s #%u sch_send %s\n",tintstr(),sender->id(),
 543                     tintstr(send_time));
 544             sender->Send();
 545             sender->Reschedule();
 546
 547         } else {  // it's too early, wait
 548
 549             tint towait = min(limit,send_time) - NOW;
 550             dprintf("%s #0 waiting %lliusec\n",tintstr(),towait);
 551             int rd = Datagram::Wait(socket_count,sockets,towait);
 552             if (rd!=INVALID_SOCKET) { // in meantime, received something
 553                 Channel* receiver = RecvDatagram(rd);
 554                 if (receiver) // receiver's state may have changed
 555                     receiver->Reschedule();
 556             }
 557             if (sender)  // get back to that later
 558                 send_queue.push(tintbin(send_time,sender->id()));
 559
 560         }
 561
 562     } while (NOW<limit);
 563
 564 }
 565
 566
 567 void Channel::Close () {
 568     this->SwitchSendControl(CLOSE_CONTROL);
 569 }
 570
 571
 572 void Channel::Reschedule () {
 573     next_send_time_ = NextSendTime();
 574     if (next_send_time_!=TINT_NEVER) {
 575         assert(next_send_time_<NOW+TINT_MIN);
 576         send_queue.push(tintbin(next_send_time_,id_));
 577         dprintf("%s #%u requeue for %s\n",tintstr(),id_,tintstr(next_send_time_));
 578     } else {
 579         dprintf("%s #%u closed\n",tintstr(),id_);
 580         delete this;
 581     }
 582 }