Cast: reduce the amount of retransmission packets

media/cast/transport/rtp_sender/rtp_sender.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/cast/transport/rtp_sender/rtp_sender.h"
 
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "media/cast/transport/cast_transport_defines.h"
 #include "media/cast/transport/pacing/paced_sender.h"
@@ skipping 55 matching lines @@
   // Iterate over all frames in the list.
   for (MissingFramesAndPacketsMap::const_iterator it =
            missing_frames_and_packets.begin();
        it != missing_frames_and_packets.end();
        ++it) {
     SendPacketVector packets_to_resend;
     uint8 frame_id = it->first;
     // Set of packets that the receiver wants us to re-send.
     // If empty, we need to re-send all packets for this frame.
     const PacketIdSet& missing_packet_set = it->second;
-    bool success = false;
 
-    for (uint16 packet_id = 0; ; packet_id++) {
-      // Get packet from storage.
-      success = storage_->GetPacket(frame_id, packet_id, &packets_to_resend);
+    const SendPacketVector* stored_packets = storage_->GetFrame8(frame_id);
+    if (!stored_packets)
+      continue;
 
-      // Check that we got at least one packet.
-      DCHECK(packet_id != 0 || success)
-          << "Failed to resend frame " << static_cast<int>(frame_id);
+    for (SendPacketVector::const_iterator it = stored_packets->begin();
+         it != stored_packets->end(); ++it) {
+      const PacketKey& packet_key = it->first;
+      const uint16 packet_id = packet_key.second.second;
 
-      if (!success) break;
-
+      // If the resend request doesn't include this packet then cancel
+      // re-transmission already in queue.
       if (!missing_packet_set.empty() &&
           missing_packet_set.find(packet_id) == missing_packet_set.end()) {
-        transport_->CancelSendingPacket(packets_to_resend.back().first);
-        packets_to_resend.pop_back();
+        transport_->CancelSendingPacket(it->first);
       } else {
         // Resend packet to the network.
         VLOG(3) << "Resend " << static_cast<int>(frame_id) << ":"
                 << packet_id;
         // Set a unique incremental sequence number for every packet.
-        PacketRef packet = packets_to_resend.back().second;
-        UpdateSequenceNumber(&packet->data);
+        PacketRef packet_copy = PacketStorage::FastCopyPacket(it->second);

[miu, 2014/06/07 00:59:42]

Dumb question: Why would we ever want a deep copy of a packet?

[Alpha Left Google, 2014/06/07 01:15:09]

Because the pacer could have one shallow in the queue. The second copy has a
different sequence number in the RTP header although packet content is the same.

[miu, 2014/06/07 02:00:09]

Okay.  We can clean this up in a later change.  It doesn't feel right to have to
copy packet data just to change the sequence number.

+        UpdateSequenceNumber(&packet_copy->data);
+        packets_to_resend.push_back(std::make_pair(packet_key, packet_copy));
       }
     }
     transport_->ResendPackets(packets_to_resend);
   }
 }
 
 void RtpSender::UpdateSequenceNumber(Packet* packet) {
   uint16 new_sequence_number = packetizer_->NextSequenceNumber();
   int index = 2;
   (*packet)[index] = (static_cast<uint8>(new_sequence_number));
   (*packet)[index + 1] = (static_cast<uint8>(new_sequence_number >> 8));
 }
 
 }  // namespace transport
 }  //  namespace cast
 }  // namespace media