Cast: Avoid retransmit if we sent the same packet recently (less than RTT)

media/cast/transport/pacing/paced_sender.cc

Index: media/cast/transport/pacing/paced_sender.cc
diff --git a/media/cast/transport/pacing/paced_sender.cc b/media/cast/transport/pacing/paced_sender.cc
index 10b42240759a3fd2c2580f802a7ed3b1e8b473ea..412a21026e207ec4e497a1eee9ba816cab16c32d 100644
--- a/media/cast/transport/pacing/paced_sender.cc
+++ b/media/cast/transport/pacing/paced_sender.cc
@@ -73,11 +73,22 @@ bool PacedSender::SendPackets(const SendPacketVector& packets) {
   return true;
 }
 
-bool PacedSender::ResendPackets(const SendPacketVector& packets) {
+bool PacedSender::ResendPackets(const SendPacketVector& packets,
+                                base::TimeDelta rtt) {
+  VLOG(0) << "RESENDPACKETS!!!!!!!";

[Alpha Left Google, 2014/06/18 01:43:32]

This shouldn't be there.

[hubbe, 2014/06/18 20:22:28]

Already gone.

   if (packets.empty()) {
     return true;
   }
+  base::TimeTicks now = clock_->NowTicks();
   for (size_t i = 0; i < packets.size(); i++) {
+    std::map<PacketKey, base::TimeTicks>::const_iterator j =
+        sent_time_.find(packets[i].first);
+
+    if (j != sent_time_.end() && now - j->second < rtt) {
+      // TODO(hubbe): Log this.

[Alpha Left Google, 2014/06/18 01:43:32]

We should log a PACKET_RTX_REJECTED event in the log.

See here:
https://code.google.com/p/chromium/codesearch#chromium/src/media/cast/logging...

It is important to evaluate the impact of this change from logs. Once we have a
good and proven algorithm then we can drop the event later.

[hubbe, 2014/06/18 20:22:28]

Done.

+      continue;
+    }
+
     packet_list_[packets[i].first] =
         make_pair(PacketType_Resend, packets[i].second);
   }
@@ -108,11 +119,13 @@ void PacedSender::CancelSendingPacket(const PacketKey& packet_key) {
   packet_list_.erase(packet_key);
 }
 
-PacketRef PacedSender::GetNextPacket(PacketType* packet_type) {
+PacketRef PacedSender::GetNextPacket(PacketType* packet_type,
+                                     PacketKey* packet_key) {
   std::map<PacketKey, std::pair<PacketType, PacketRef> >::iterator i;
   i = packet_list_.begin();
   DCHECK(i != packet_list_.end());
   *packet_type = i->second.first;
+  *packet_key = i->first;
   PacketRef ret = i->second.second;
   packet_list_.erase(i);
   return ret;
@@ -134,6 +147,13 @@ size_t PacedSender::size() const {
 //    case we called PostDelayedTask on this function to start a new burst.
 void PacedSender::SendStoredPackets() {
   State previous_state = state_;
+
+  if (state_ == State_TransportBlocked) {
+    base::TimeTicks sent_time = clock_->NowTicks();
+    sent_time_[in_progress_packet_key_] = sent_time;
+    sent_time_buffer_[in_progress_packet_key_] = sent_time;
+  }
+
   state_ = State_Unblocked;
   if (empty()) {
     return;
@@ -185,7 +205,8 @@ void PacedSender::SendStoredPackets() {
       return;
     }
     PacketType packet_type;
-    PacketRef packet = GetNextPacket(&packet_type);
+    PacketRef packet = GetNextPacket(&packet_type,
+                                     &in_progress_packet_key_);
 
     switch (packet_type) {
       case PacketType_Resend:
@@ -202,6 +223,14 @@ void PacedSender::SendStoredPackets() {
       return;
     }
     current_burst_size_++;
+    base::TimeTicks sent_time = clock_->NowTicks();
+    sent_time_[in_progress_packet_key_] = sent_time;
+    sent_time_buffer_[in_progress_packet_key_] = sent_time;
+  }
+  // Keep ~1 second of data (1000 packets)
+  if (sent_time_buffer_.size() > kMaxBurstSize * 1000 / kPacingIntervalMs) {

[Alpha Left Google, 2014/06/18 01:43:32]

nit: Define 1000 as a constant at the top of this file.

[hubbe, 2014/06/18 20:22:27]

It's just the number of milliseconds in a second.
Do we really need a constant for that?

+    sent_time_.swap(sent_time_buffer_);
+    sent_time_buffer_.clear();
   }
   state_ = State_Unblocked;

[Alpha Left Google, 2014/06/18 01:43:32]

Please put a DCHECK for the sizes of the sent_time_ and sent_time_buffer_.

[hubbe, 2014/06/18 20:22:27]

Done.

 }