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 "compat/util.h"
  11
  12
  13 using namespace swift;
  14 using namespace std;
  15
  16 /*
  17  TODO  25 Oct 18:55
  18  - range: ALL
  19  - randomized testing of advanced ops (new testcase)
  20  */
  21
  22 void    Channel::AddPeakHashes (Datagram& dgram) {
  23     for(int i=0; i<file().peak_count(); i++) {
  24         bin64_t peak = file().peak(i);
  25         dgram.Push8(SWIFT_HASH);
  26         dgram.Push32((uint32_t)peak);
  27         dgram.PushHash(file().peak_hash(i));
  28         //DLOG(INFO)<<"#"<<id<<" +pHASH"<<file().peak(i);
  29         dprintf("%s #%u +phash %s\n",tintstr(),id_,peak.str());
  30     }
  31 }
  32
  33
  34 void    Channel::AddUncleHashes (Datagram& dgram, bin64_t pos) {
  35     bin64_t peak = file().peak_for(pos);
  36     while (pos!=peak && ((NOW&3)==3 || !data_out_cap_.within(pos.parent())) &&
  37             ack_in_.get(pos.parent())==binmap_t::EMPTY  ) {
  38         bin64_t uncle = pos.sibling();
  39         dgram.Push8(SWIFT_HASH);
  40         dgram.Push32((uint32_t)uncle);
  41         dgram.PushHash( file().hash(uncle) );
  42         //DLOG(INFO)<<"#"<<id<<" +uHASH"<<uncle;
  43         dprintf("%s #%u +hash %s\n",tintstr(),id_,uncle.str());
  44         pos = pos.parent();
  45     }
  46 }
  47
  48
  49 bin64_t        Channel::DequeueHint () {
  50     if (hint_in_.empty() && last_recv_time_>NOW-rtt_avg_-TINT_SEC) {
  51         uint64_t twist = peer_channel_id_;  // got no hints, send something randomly
  52         twist &= file().peak(0); // may make it semi-seq here
  53         file().ack_out().twist(twist);
  54         ack_in_.twist(twist);
  55         bin64_t my_pick =
  56             file().ack_out().find_filtered(ack_in_,bin64_t::ALL,binmap_t::FILLED);
  57         while (my_pick.width()>max(1,(int)cwnd_))
  58             my_pick = my_pick.left();
  59         file().ack_out().twist(0);
  60         ack_in_.twist(0);
  61         if (my_pick!=bin64_t::NONE) {
  62             my_pick = my_pick.twisted(twist);
  63             hint_in_.push_back(my_pick);
  64             dprintf("%s #%u *hint %s\n",tintstr(),id_,my_pick.str());
  65         }
  66     }
  67     bin64_t send = bin64_t::NONE;
  68     while (!hint_in_.empty() && send==bin64_t::NONE) {
  69         bin64_t hint = hint_in_.front().bin;
  70         tint time = hint_in_.front().time;
  71         hint_in_.pop_front();
  72         while (!hint.is_base()) { // FIXME optimize; possible attack
  73             hint_in_.push_front(tintbin(time,hint.right()));
  74             hint = hint.left();
  75         }
  76         //if (time < NOW-TINT_SEC*3/2 )
  77         //    continue;  bad idea
  78         if (ack_in_.get(hint)!=binmap_t::FILLED)
  79             send = hint;
  80     }
  81     uint64_t mass = 0;
  82     for(int i=0; i<hint_in_.size(); i++)
  83         mass += hint_in_[i].bin.width();
  84     dprintf("%s #%u dequeued %s [%lli]\n",tintstr(),id_,send.str(),mass);
  85     return send;
  86 }
  87
  88
  89 void    Channel::AddHandshake (Datagram& dgram) {
  90     if (!peer_channel_id_) { // initiating
  91         dgram.Push8(SWIFT_HASH);
  92         dgram.Push32(bin64_t::ALL32);
  93         dgram.PushHash(file().root_hash());
  94         dprintf("%s #%u +hash ALL %s\n",
  95                 tintstr(),id_,file().root_hash().hex().c_str());
  96     }
  97     dgram.Push8(SWIFT_HANDSHAKE);
  98     int encoded = EncodeID(id_);
  99     dgram.Push32(encoded);
 100     dprintf("%s #%u +hs %x\n",tintstr(),id_,encoded);
 101     ack_out_.clear();
 102     AddAck(dgram);
 103 }
 104
 105
 106 void    Channel::Send () {
 107     Datagram dgram(socket_,peer());
 108     dgram.Push32(peer_channel_id_);
 109     bin64_t data = bin64_t::NONE;
 110     if ( is_established() ) {
 111         // FIXME: seeder check
 112         AddAck(dgram);
 113         if (!file().is_complete())
 114             AddHint(dgram);
 115         AddPex(dgram);
 116         CleanDataOut();
 117         data = AddData(dgram);
 118     } else {
 119         AddHandshake(dgram);
 120         AddAck(dgram);
 121     }
 122     dprintf("%s #%u sent %ib %s:%x\n",
 123             tintstr(),id_,dgram.size(),peer().str(),peer_channel_id_);
 124     if (dgram.size()==4) {// only the channel id; bare keep-alive
 125         data = bin64_t::ALL;
 126         //dprintf("%s #%u considering keepalive %i %f %s\n",
 127         //        tintstr(),id_,(int)data_out_.size(),cwnd_,SEND_CONTROL_MODES[send_control_]);
 128         //if (data_out_.size()<cwnd_ && send_control_!=KEEP_ALIVE_CONTROL) {
 129             //if ( cwnd_ < 1 )
 130             //    SwitchSendControl(KEEP_ALIVE_CONTROL);
 131             //else
 132             //    cwnd_ = cwnd_/2.0;
 133         //}
 134         //if (data_out_.empty() && send_control_!=KEEP_ALIVE_CONTROL)
 135         //     SwitchSendControl(KEEP_ALIVE_CONTROL);// we did our best
 136         //if (NOW<last_send_time_+MAX_SEND_INTERVAL) // no need for keepalive
 137         //    return; // don't send empty dgram
 138     }
 139     if (dgram.Send()==-1)
 140         print_error("can't send datagram");
 141     last_send_time_ = NOW;
 142     sent_since_recv_++;
 143     dgrams_sent_++;
 144 }
 145
 146
 147 void    Channel::AddHint (Datagram& dgram) {
 148
 149     tint plan_for = max(TINT_SEC,rtt_avg_*4);
 150
 151     tint timed_out = NOW - plan_for*2;
 152     while ( !hint_out_.empty() && hint_out_.front().time < timed_out ) {
 153         hint_out_size_ -= hint_out_.front().bin.width();
 154         hint_out_.pop_front();
 155     }
 156
 157     /*int peer_cwnd = (int)(rtt_avg_ / dip_avg_);
 158     if (!peer_cwnd)
 159         peer_cwnd = 1;*/
 160     int plan_pck = std::max ( (tint)1, plan_for / dip_avg_ );
 161
 162     if ( hint_out_size_ < plan_pck ) {
 163
 164         int diff = plan_pck - hint_out_size_; // TODO: aggregate
 165         bin64_t hint = transfer().picker().Pick(ack_in_,diff,NOW+plan_for*2);
 166
 167         if (hint!=bin64_t::NONE) {
 168             dgram.Push8(SWIFT_HINT);
 169             dgram.Push32(hint);
 170             dprintf("%s #%u +hint %s [%lli]\n",tintstr(),id_,hint.str(),hint_out_size_);
 171             hint_out_.push_back(hint);
 172             hint_out_size_ += hint.width();
 173         } else
 174             dprintf("%s #%u Xhint\n",tintstr(),id_);
 175
 176     }
 177 }
 178
 179
 180 bin64_t        Channel::AddData (Datagram& dgram) {
 181
 182     if (!file().size()) // know nothing
 183         return bin64_t::NONE;
 184
 185     bin64_t tosend = bin64_t::NONE;
 186     if (data_out_.size()<cwnd_ && last_data_out_time_<=NOW-send_interval_) {
 187         tosend = DequeueHint();
 188         if (tosend==bin64_t::NONE) {
 189             dprintf("%s #%u no idea what to send #sendctrl\n",tintstr(),id_);
 190             if (send_control_!=KEEP_ALIVE_CONTROL)
 191                 SwitchSendControl(KEEP_ALIVE_CONTROL);
 192         }
 193     } else
 194         dprintf("%s #%u no cwnd #sendctrl\n",tintstr(),id_);
 195
 196     if (tosend==bin64_t::NONE)// && (last_data_out_time_>NOW-TINT_SEC || data_out_.empty()))
 197         return bin64_t::NONE; // once in a while, empty data is sent just to check rtt FIXED
 198
 199     if (ack_in_.is_empty() && file().size())
 200         AddPeakHashes(dgram);
 201     AddUncleHashes(dgram,tosend);
 202     if (!ack_in_.is_empty()) // TODO: cwnd_>1
 203         data_out_cap_ = tosend;
 204
 205     if (dgram.size()>254) {
 206         dgram.Send(); // kind of fragmentation
 207         dgram.Push32(peer_channel_id_);
 208     }
 209
 210     dgram.Push8(SWIFT_DATA);
 211     dgram.Push32(tosend.to32());
 212
 213     uint8_t buf[1024];
 214     size_t r = pread(file().file_descriptor(),buf,1024,tosend.base_offset()<<10);
 215     // TODO: corrupted data, retries, caching
 216     if (r<0) {
 217         print_error("error on reading");
 218         return bin64_t::NONE;
 219     }
 220     assert(dgram.space()>=r+4+1);
 221     dgram.Push(buf,r);
 222
 223     last_data_out_time_ = NOW;
 224     data_out_.push_back(tosend);
 225     dprintf("%s #%u +data %s\n",tintstr(),id_,tosend.str());
 226
 227     return tosend;
 228 }
 229
 230
 231 void    Channel::AddTs (Datagram& dgram) {
 232     dgram.Push8(SWIFT_TS);
 233     dgram.Push64(data_in_.time);
 234     dprintf("%s #%u +ts %s\n",tintstr(),id_,tintstr(data_in_.time));
 235 }
 236
 237
 238 void    Channel::AddAck (Datagram& dgram) {
 239     if (data_in_dbl_!=bin64_t::NONE) { // TODO: do redundancy better
 240         dgram.Push8(SWIFT_ACK);
 241         dgram.Push32(data_in_dbl_.to32());
 242         data_in_dbl_=bin64_t::NONE;
 243     }
 244     if (data_in_.time!=TINT_NEVER) { // TODO: ACK NONE for corrupted data
 245         AddTs(dgram);
 246         bin64_t pos = file().ack_out().cover(data_in_.bin);
 247         dgram.Push8(SWIFT_ACK);
 248         dgram.Push32(pos.to32());
 249         //dgram.Push64(data_in_.time);
 250         ack_out_.set(pos);
 251         dprintf("%s #%u +ack %s %s\n",tintstr(),id_,pos.str(),tintstr(data_in_.time));
 252         data_in_ = tintbin(TINT_NEVER,bin64_t::NONE);
 253         if (pos.layer()>2)
 254             data_in_dbl_ = pos;
 255     }
 256     for(int count=0; count<4; count++) {
 257         bin64_t ack = file().ack_out().find_filtered(ack_out_, bin64_t::ALL, binmap_t::FILLED);
 258         if (ack==bin64_t::NONE)
 259             break;
 260         ack = file().ack_out().cover(ack);
 261         ack_out_.set(ack);
 262         dgram.Push8(SWIFT_ACK);
 263         dgram.Push32(ack.to32());
 264         dprintf("%s #%u +ack %s\n",tintstr(),id_,ack.str());
 265     }
 266 }
 267
 268
 269 void    Channel::Recv (Datagram& dgram) {
 270     dprintf("%s #%u recvd %i\n",tintstr(),id_,dgram.size()+4);
 271     peer_send_time_ = 0; // has scope of 1 datagram
 272     dgrams_rcvd_++;
 273     if (last_send_time_ && rtt_avg_==TINT_SEC && dev_avg_==0) {
 274         rtt_avg_ = NOW - last_send_time_;
 275         dev_avg_ = rtt_avg_;
 276         dip_avg_ = rtt_avg_;
 277         dprintf("%s #%u rtt init %lli\n",tintstr(),id_,rtt_avg_);
 278     }
 279     bin64_t data = dgram.size() ? bin64_t::NONE : bin64_t::ALL;
 280     while (dgram.size()) {
 281         uint8_t type = dgram.Pull8();
 282         switch (type) {
 283             case SWIFT_HANDSHAKE: OnHandshake(dgram); break;
 284             case SWIFT_DATA:      data=OnData(dgram); break;
 285             case SWIFT_TS:        OnTs(dgram); break;
 286             case SWIFT_ACK:       OnAck(dgram); break;
 287             case SWIFT_HASH:      OnHash(dgram); break;
 288             case SWIFT_HINT:      OnHint(dgram); break;
 289             case SWIFT_PEX_ADD:   OnPex(dgram); break;
 290             default:
 291                 eprintf("%s #%u ?msg id unknown %i\n",tintstr(),id_,(int)type);
 292                 return;
 293         }
 294     }
 295     last_recv_time_ = NOW;
 296     sent_since_recv_ = 0;
 297 }
 298
 299
 300 void    Channel::OnHash (Datagram& dgram) {
 301     bin64_t pos = dgram.Pull32();
 302     Sha1Hash hash = dgram.PullHash();
 303     file().OfferHash(pos,hash);
 304     //DLOG(INFO)<<"#"<<id<<" .HASH"<<(int)pos;
 305     dprintf("%s #%u -hash %s\n",tintstr(),id_,pos.str());
 306 }
 307
 308
 309 void    Channel::CleanHintOut (bin64_t pos) {
 310     int hi = 0;
 311     while (hi<hint_out_.size() && !pos.within(hint_out_[hi].bin))
 312         hi++;
 313     if (hi==hint_out_.size())
 314         return; // something not hinted or hinted in far past
 315     while (hi--) { // removing likely snubbed hints
 316         hint_out_size_ -= hint_out_.front().bin.width();
 317         hint_out_.pop_front();
 318     }
 319     while (hint_out_.front().bin!=pos) {
 320         tintbin f = hint_out_.front();
 321         f.bin = f.bin.towards(pos);
 322         hint_out_.front().bin = f.bin.sibling();
 323         hint_out_.push_front(f);
 324     }
 325     hint_out_.pop_front();
 326     hint_out_size_--;
 327 }
 328
 329
 330 bin64_t Channel::OnData (Datagram& dgram) {
 331     bin64_t pos = dgram.Pull32();
 332     uint8_t *data;
 333     int length = dgram.Pull(&data,1024);
 334     bool ok = (pos==bin64_t::NONE) || file().OfferData(pos, (char*)data, length) ;
 335     dprintf("%s #%u %cdata %s\n",tintstr(),id_,ok?'-':'!',pos.str());
 336     data_in_ = tintbin(NOW,bin64_t::NONE);
 337     if (!ok)
 338         return bin64_t::NONE;
 339     data_in_.bin = pos;
 340     if (pos!=bin64_t::NONE) {
 341         if (last_data_in_time_) {
 342             tint dip = NOW - last_data_in_time_;
 343             dip_avg_ = ( dip_avg_*3 + dip ) >> 2;
 344         }
 345         last_data_in_time_ = NOW;
 346     }
 347     CleanHintOut(pos);
 348     return pos;
 349 }
 350
 351
 352 void    Channel::CleanDataOut (bin64_t ackd_pos) { // TODO: isn't it too long?
 353
 354     int max_ack_off = 0;
 355     //FIXME do LEDBAT magic somewhere here
 356
 357     if (ackd_pos!=bin64_t::NONE) {
 358         for (int i=0; i<8 && i<data_out_.size(); i++) {
 359             if (data_out_[i]!=tintbin() && data_out_[i].bin.within(ackd_pos)) {
 360                 tint rtt = NOW-data_out_[i].time;
 361                 rtt_avg_ = (rtt_avg_*7 + rtt) >> 3;
 362                 dev_avg_ = ( dev_avg_*3 + abs(rtt-rtt_avg_) ) >> 2;
 363                 if (peer_send_time_) {
 364                     assert(data_out_[i].time!=TINT_NEVER);
 365                     tint owd = peer_send_time_ - data_out_[i].time;
 366                     owd_cur_bin_ = (owd_cur_bin_+1) & 3;
 367                     owd_current_[owd_cur_bin_] = owd;
 368                     if ( owd_min_bin_start_+TINT_SEC*30 < NOW ) {
 369                         owd_min_bin_start_ = NOW;
 370                         owd_min_bin_ = (owd_min_bin_+1) & 3;
 371                         owd_min_bins_[owd_min_bin_] = TINT_NEVER;
 372                     }
 373                     if (owd_min_bins_[owd_min_bin_]>owd)
 374                         owd_min_bins_[owd_min_bin_] = owd;
 375                 }
 376                 dprintf("%s #%u rtt %lli dev %lli\n",tintstr(),id_,rtt_avg_,dev_avg_);
 377                 bin64_t pos = data_out_[i].bin;
 378                 ack_rcvd_recent_++;
 379                 data_out_[i]=tintbin();
 380                 max_ack_off = i;
 381                 if (ackd_pos==pos)
 382                     break;
 383             }
 384         }
 385         while (!data_out_.empty() && data_out_.front().bin==bin64_t::NONE) {
 386             data_out_.pop_front();
 387             max_ack_off--;
 388         }
 389         static const int MAX_REORDERING = 2;  // the triple-ACK principle
 390         if (max_ack_off>MAX_REORDERING) {
 391             while (max_ack_off && (data_out_.front().bin==bin64_t::NONE
 392                                    || ack_in_.is_filled(data_out_.front().bin)) ) {
 393                 data_out_.pop_front();
 394                 max_ack_off--;
 395             }
 396             while (max_ack_off>MAX_REORDERING) {
 397                 ack_not_rcvd_recent_++;
 398                 dprintf("%s #%u Rdata %s\n",tintstr(),id_,data_out_.front().bin.str());
 399                 data_out_.pop_front();
 400                 max_ack_off--;
 401                 data_out_cap_ = bin64_t::ALL;
 402             }
 403         }
 404     }
 405     tint timeout = NOW - rtt_avg_ - 4*std::max(dev_avg_,TINT_MSEC*50);
 406     while (!data_out_.empty() && data_out_.front().time<timeout) {
 407         if (data_out_.front().bin!=bin64_t::NONE && ack_in_.is_empty(data_out_.front().bin)) {
 408             ack_not_rcvd_recent_++;
 409             data_out_cap_ = bin64_t::ALL;
 410             dprintf("%s #%u Tdata %s\n",tintstr(),id_,data_out_.front().bin.str());
 411         }
 412         data_out_.pop_front();
 413     }
 414     while (!data_out_.empty() && data_out_.front().bin==bin64_t::NONE)
 415         data_out_.pop_front();
 416
 417 }
 418
 419
 420 void    Channel::OnAck (Datagram& dgram) {
 421     bin64_t ackd_pos = dgram.Pull32();
 422     if (ackd_pos==bin64_t::NONE)
 423         return; // likely, brocken packet / insufficient hashes
 424     if (file().size() && ackd_pos.base_offset()>=file().packet_size()) {
 425         eprintf("invalid ack: %s\n",ackd_pos.str());
 426         return;
 427     }
 428     dprintf("%s #%u -ack %s\n",tintstr(),id_,ackd_pos.str());
 429     ack_in_.set(ackd_pos);
 430     CleanDataOut(ackd_pos); // FIXME do AFTER all ACKs
 431 }
 432
 433
 434 void Channel::OnTs (Datagram& dgram) {
 435     peer_send_time_ = dgram.Pull64();
 436     dprintf("%s #%u -ts %lli\n",tintstr(),id_,peer_send_time_);
 437 }
 438
 439
 440 void    Channel::OnHint (Datagram& dgram) {
 441     bin64_t hint = dgram.Pull32();
 442     hint_in_.push_back(hint);
 443     //ack_in_.set(hint,binmap_t::EMPTY);
 444     //RequeueSend(cc_->OnHintRecvd(hint));
 445     dprintf("%s #%u -hint %s\n",tintstr(),id_,hint.str());
 446 }
 447
 448
 449 void Channel::OnHandshake (Datagram& dgram) {
 450     peer_channel_id_ = dgram.Pull32();
 451     dprintf("%s #%u -hs %x\n",tintstr(),id_,peer_channel_id_);
 452     // self-connection check
 453     if (!SELF_CONN_OK) {
 454         uint32_t try_id = DecodeID(peer_channel_id_);
 455         if (channel(try_id) && !channel(try_id)->peer_channel_id_) {
 456             peer_channel_id_ = 0;
 457             Close();
 458             return; // this is a self-connection
 459         }
 460     }
 461     // FUTURE: channel forking
 462 }
 463
 464
 465 void Channel::OnPex (Datagram& dgram) {
 466     uint32_t ipv4 = dgram.Pull32();
 467     uint16_t port = dgram.Pull16();
 468     Address addr(ipv4,port);
 469     dprintf("%s #%u -pex %s\n",tintstr(),id_,addr.str());
 470     transfer().OnPexIn(addr);
 471 }
 472
 473
 474 void    Channel::AddPex (Datagram& dgram) {
 475     int chid = transfer().RevealChannel(pex_out_);
 476     if (chid==-1 || chid==id_)
 477         return;
 478     Address a = channels[chid]->peer();
 479     dgram.Push8(SWIFT_PEX_ADD);
 480     dgram.Push32(a.ipv4());
 481     dgram.Push16(a.port());
 482     dprintf("%s #%u +pex %s\n",tintstr(),id_,a.str());
 483 }
 484
 485
 486 Channel*    Channel::RecvDatagram (int socket) {
 487     Datagram data(socket);
 488     data.Recv();
 489     const Address& addr = data.address();
 490 #define return_log(...) { printf(__VA_ARGS__); return NULL; }
 491     if (data.size()<4)
 492         return_log("datagram shorter than 4 bytes %s\n",addr.str());
 493     uint32_t mych = data.Pull32();
 494     Sha1Hash hash;
 495     Channel* channel = NULL;
 496     if (!mych) { // handshake initiated
 497         if (data.size()<1+4+1+4+Sha1Hash::SIZE)
 498             return_log ("%s #0 incorrect size %i initial handshake packet %s\n",
 499                         tintstr(),data.size(),addr.str());
 500         uint8_t hashid = data.Pull8();
 501         if (hashid!=SWIFT_HASH)
 502             return_log ("%s #0 no hash in the initial handshake %s\n",
 503                         tintstr(),addr.str());
 504         bin64_t pos = data.Pull32();
 505         if (pos!=bin64_t::ALL)
 506             return_log ("%s #0 that is not the root hash %s\n",tintstr(),addr.str());
 507         hash = data.PullHash();
 508         FileTransfer* file = FileTransfer::Find(hash);
 509         if (!file)
 510             return_log ("%s #0 hash %s unknown, no such file %s\n",tintstr(),hash.hex().c_str(),addr.str());
 511         dprintf("%s #0 -hash ALL %s\n",tintstr(),hash.hex().c_str());
 512         for(binqueue::iterator i=file->hs_in_.begin(); i!=file->hs_in_.end(); i++)
 513             if (channels[*i] && channels[*i]->peer_==data.address() &&
 514                 channels[*i]->last_recv_time_>NOW-TINT_SEC*2)
 515                 return_log("%s #0 have a channel already to %s\n",tintstr(),addr.str());
 516         channel = new Channel(file, socket, data.address());
 517     } else {
 518         mych = DecodeID(mych);
 519         if (mych>=channels.size())
 520             return_log("%s invalid channel #%u, %s\n",tintstr(),mych,addr.str());
 521         channel = channels[mych];
 522         if (!channel)
 523             return_log ("%s #%u is already closed\n",tintstr(),mych,addr.str());
 524         if (channel->peer() != addr)
 525             return_log ("%s #%u invalid peer address %s!=%s\n",
 526                         tintstr(),mych,channel->peer().str(),addr.str());
 527         channel->own_id_mentioned_ = true;
 528     }
 529     //dprintf("recvd %i bytes for %i\n",data.size(),channel->id);
 530     channel->Recv(data);
 531     return channel;
 532 }
 533
 534
 535 void    Channel::Loop (tint howlong) {
 536
 537     tint limit = Datagram::Time() + howlong;
 538
 539     do {
 540
 541         tint send_time(TINT_NEVER);
 542         Channel* sender(NULL);
 543         while (!sender && !send_queue.is_empty()) { // dequeue
 544             tintbin next = send_queue.pop();
 545             sender = channel((int)next.bin);
 546             send_time = next.time;
 547             if (sender && sender->next_send_time_!=send_time &&
 548                      sender->next_send_time_!=TINT_NEVER )
 549                 sender = NULL; // it was a stale entry
 550         }
 551
 552         if ( sender!=NULL && send_time<=NOW ) { // it's time
 553
 554             dprintf("%s #%u sch_send %s\n",tintstr(),sender->id(),
 555                     tintstr(send_time));
 556             sender->Send();
 557             sender->Reschedule();
 558
 559         } else {  // it's too early, wait
 560
 561             tint towait = min(limit,send_time) - NOW;
 562             dprintf("%s waiting %lliusec\n",tintstr(),towait);
 563             int rd = Datagram::Wait(socket_count,sockets,towait);
 564             if (rd!=INVALID_SOCKET) { // in meantime, received something
 565                 Channel* receiver = RecvDatagram(rd);
 566                 if (receiver) // receiver's state may have changed
 567                     receiver->Reschedule();
 568             }
 569             if (sender)  // get back to that later
 570                 send_queue.push(tintbin(send_time,sender->id()));
 571
 572         }
 573
 574     } while (NOW<limit);
 575
 576 }
 577
 578
 579 void Channel::Close () {
 580     this->SwitchSendControl(CLOSE_CONTROL);
 581 }
 582
 583
 584 void Channel::Reschedule () {
 585     next_send_time_ = NextSendTime();
 586     if (next_send_time_!=TINT_NEVER) {
 587         assert(next_send_time_<NOW+TINT_MIN);
 588         send_queue.push(tintbin(next_send_time_,id_));
 589         dprintf("%s requeue #%u for %s\n",tintstr(),id_,tintstr(next_send_time_));
 590     } else {
 591         dprintf("%s #%u closed\n",tintstr(),id_);
 592         delete this;
 593     }
 594 }