Adds an alarm for sending a QUIC FEC packet.

net/quic/quic_packet_generator.cc

 // Copyright (c) 2012 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 "net/quic/quic_packet_generator.h"
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "net/quic/quic_ack_notifier.h"
 #include "net/quic/quic_fec_group.h"
 #include "net/quic/quic_flags.h"
 #include "net/quic/quic_utils.h"
 
 using base::StringPiece;
 
 namespace net {
 
 namespace {
 
 // We want to put some space between a protected packet and the FEC packet to
-// avoid losing them both within the same loss episode. On the other hand,
-// we expect to be able to recover from any loss in about an RTT.
-// We resolve this tradeoff by sending an FEC packet atmost half an RTT,
-// or equivalently, half the max number of in-flight packets,  the first
-// protected packet. Since we don't want to delay an FEC packet past half an
-// RTT, we set the max FEC group size to be half the current congestion window.
+// avoid losing them both within the same loss episode. On the other hand, we
+// expect to be able to recover from any loss in about an RTT. We resolve this
+// tradeoff by sending an FEC packet atmost half an RTT, or equivalently, half
+// the max number of in-flight packets,  the first protected packet. Since we
+// don't want to delay an FEC packet past half an RTT, we set the max FEC group
+// size to be half the current congestion window.
 const float kMaxPacketsInFlightMultiplierForFecGroupSize = 0.5;
 const float kRttMultiplierForFecTimeout = 0.5;
 
+// Minimum timeout for FEC alarm, set to half the minimum Tail Loss Probe
+// timeout of 10ms.
+const int64 kMinFecTimeoutMs = 5u;
+
 }  // namespace
 
 class QuicAckNotifier;
 
 QuicPacketGenerator::QuicPacketGenerator(QuicConnectionId connection_id,
                                          QuicFramer* framer,
                                          QuicRandom* random_generator,
                                          DelegateInterface* delegate)
     : delegate_(delegate),
       debug_delegate_(nullptr),
@@ skipping 188 matching lines @@
     delete notifier;
   }
 
   // Don't allow the handshake to be bundled with other retransmittable frames.
   if (handshake == IS_HANDSHAKE) {
     SendQueuedFrames(true);
   }
 
   // Try to close FEC group since we've either run out of data to send or we're
   // blocked. If not in batch mode, force close the group.
-  // TODO(jri): This method should be called with flush=false here
-  // once the timer-based FEC sending is done, to separate FEC sending from
-  // the end of batch operations.
-  MaybeSendFecPacketAndCloseGroup(!InBatchMode());
+  MaybeSendFecPacketAndCloseGroup(/*flush=*/false);
 
   DCHECK(InBatchMode() || !packet_creator_.HasPendingFrames());
   return QuicConsumedData(total_bytes_consumed, fin_consumed);
 }
 
 bool QuicPacketGenerator::CanSendWithNextPendingFrameAddition() const {
   DCHECK(HasPendingFrames());
   HasRetransmittableData retransmittable =
       (should_send_ack_ || should_send_feedback_ || should_send_stop_waiting_)
       ? NO_RETRANSMITTABLE_DATA : HAS_RETRANSMITTABLE_DATA;
   if (retransmittable == HAS_RETRANSMITTABLE_DATA) {
       DCHECK(!queued_control_frames_.empty());  // These are retransmittable.
   }
   return delegate_->ShouldGeneratePacket(NOT_RETRANSMISSION, retransmittable,
                                          NOT_HANDSHAKE);
 }
 
 void QuicPacketGenerator::SendQueuedFrames(bool flush) {
   // Only add pending frames if we are SURE we can then send the whole packet.
   while (HasPendingFrames() &&
          (flush || CanSendWithNextPendingFrameAddition())) {
     if (!AddNextPendingFrame()) {
       // Packet was full, so serialize and send it.
       SerializeAndSendPacket();
     }
   }
-
-  if (!InBatchMode() || flush) {
-    if (packet_creator_.HasPendingFrames()) {
-      SerializeAndSendPacket();
-    }
-    // Ensure the FEC group is closed at the end of this method unless other
-    // writes are pending.
-    MaybeSendFecPacketAndCloseGroup(true);
+  if (packet_creator_.HasPendingFrames() && (flush || !InBatchMode())) {
+    SerializeAndSendPacket();
   }
+  MaybeSendFecPacketAndCloseGroup(flush);
 }
 
 void QuicPacketGenerator::MaybeStartFecProtection() {
   if (!packet_creator_.IsFecEnabled()) {
     return;
   }
   DVLOG(1) << "Turning FEC protection ON";
   should_fec_protect_ = true;
   if (packet_creator_.IsFecProtected()) {
     // Only start creator's FEC protection if not already on.
     return;
   }
   if (HasQueuedFrames()) {
     // TODO(jri): This currently requires that the generator flush out any
     // pending frames when FEC protection is turned on. If current packet can be
     // converted to an FEC protected packet, do it. This will require the
     // generator to check if the resulting expansion still allows the incoming
     // frame to be added to the packet.
     SendQueuedFrames(true);
   }
   packet_creator_.StartFecProtectingPackets();
   DCHECK(packet_creator_.IsFecProtected());
 }
 
 void QuicPacketGenerator::MaybeSendFecPacketAndCloseGroup(bool force) {
-  if (!packet_creator_.IsFecProtected() ||
-      packet_creator_.HasPendingFrames() ||
-      !packet_creator_.ShouldSendFec(force)) {
+  if (!ShouldSendFecPacket(force)) {
     return;
   }
   // TODO(jri): SerializeFec can return a NULL packet, and this should
   // cause an early return, with a call to delegate_->OnPacketGenerationError.
   SerializedPacket serialized_fec = packet_creator_.SerializeFec();
   DCHECK(serialized_fec.packet);
   delegate_->OnSerializedPacket(serialized_fec);
   // Turn FEC protection off if creator's protection is on and the creator
   // does not have an open FEC group.
   // Note: We only wait until the frames queued in the creator are flushed;
   // pending frames in the generator will not keep us from turning FEC off.
   if (!should_fec_protect_ && !packet_creator_.IsFecGroupOpen()) {
     packet_creator_.StopFecProtectingPackets();
     DCHECK(!packet_creator_.IsFecProtected());
   }
 }
 
+bool QuicPacketGenerator::ShouldSendFecPacket(bool force) {
+  return packet_creator_.IsFecProtected() &&
+         !packet_creator_.HasPendingFrames() &&
+         packet_creator_.ShouldSendFec(force);
+}
+
+void QuicPacketGenerator::OnFecTimeout() {
+  DCHECK(!InBatchMode());
+  if (!ShouldSendFecPacket(true)) {
+    LOG(DFATAL) << "No FEC packet to send on FEC timeout.";
+    return;
+  }
+  // Flush out any pending frames in the generator and the creator, and then
+  // send out FEC packet.
+  SendQueuedFrames(true);
+  MaybeSendFecPacketAndCloseGroup(/*flush=*/true);
+}
+
+QuicTime::Delta QuicPacketGenerator::GetFecTimeout(
+    QuicPacketSequenceNumber sequence_number) {
+  // Do not set up FEC alarm for |sequence_number| it is not the first packet in
+  // the current group.
+  if (packet_creator_.IsFecGroupOpen() &&
+      (sequence_number == packet_creator_.fec_group_number())) {
+    return QuicTime::Delta::Max(
+        fec_timeout_, QuicTime::Delta::FromMilliseconds(kMinFecTimeoutMs));
+  }
+  return QuicTime::Delta::Infinite();
+}
+
 bool QuicPacketGenerator::InBatchMode() {
   return batch_mode_;
 }
 
 void QuicPacketGenerator::StartBatchOperations() {
   batch_mode_ = true;
 }
 
 void QuicPacketGenerator::FinishBatchOperations() {
   batch_mode_ = false;
@@ skipping 64 matching lines @@
   SerializedPacket serialized_packet = packet_creator_.SerializePacket();
   DCHECK(serialized_packet.packet);
 
   // There may be AckNotifiers interested in this packet.
   if (FLAGS_quic_attach_ack_notifiers_to_packets) {
     serialized_packet.notifiers.swap(ack_notifiers_);
     ack_notifiers_.clear();
   }
 
   delegate_->OnSerializedPacket(serialized_packet);
-  MaybeSendFecPacketAndCloseGroup(false);
+  MaybeSendFecPacketAndCloseGroup(/*flush=*/false);
 
   // The packet has now been serialized, safe to delete pending frames.
   if (FLAGS_quic_disallow_multiple_pending_ack_frames) {
     pending_ack_frame_.reset();
     pending_feedback_frame_.reset();
     pending_stop_waiting_frame_.reset();
   }
 }
 
 void QuicPacketGenerator::StopSendingVersion() {
@@ skipping 41 matching lines @@
     packet_creator_.set_connection_id_length(PACKET_8BYTE_CONNECTION_ID);
   }
 }
 
 
 void QuicPacketGenerator::set_encryption_level(EncryptionLevel level) {
   packet_creator_.set_encryption_level(level);
 }
 
 }  // namespace net