Land Recent QUIC Changes.

net/quic/congestion_control/hybrid_slow_start.h

 // 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.
 //
 // This class is a helper class to TcpCubicSender.
 // Slow start is the initial startup phase of TCP, it lasts until first packet
 // loss. This class implements hybrid slow start of the TCP cubic send side
 // congestion algorithm. The key feaure of hybrid slow start is that it tries to
 // avoid running into the wall too hard during the slow start phase, which
 // the traditional TCP implementation does.
@@ skipping 19 matching lines @@
 
   void OnPacketAcked(QuicPacketSequenceNumber acked_sequence_number,
                      bool in_slow_start);
 
   void OnPacketSent(QuicPacketSequenceNumber sequence_number,
                     QuicByteCount available_send_window);
 
   bool ShouldExitSlowStart(const RttStats* rtt_stats,
                            int64 congestion_window);
 
-  // TODO(ianswett): The following methods should be private, but that requires
-  // a follow up CL to update the unit test.
   // Start a new slow start phase.
   void Restart();
 
+  // TODO(ianswett): The following methods should be private, but that requires
+  // a follow up CL to update the unit test.
   // Returns true if this ack the last sequence number of our current slow start
   // round.
   // Call Reset if this returns true.
   bool IsEndOfRound(QuicPacketSequenceNumber ack) const;
 
   // Call for each round (burst) in the slow start phase.
   void Reset(QuicPacketSequenceNumber end_sequence_number);
 
   // rtt: it the RTT for this ack packet.
-  // delay_min: is the lowest delay (RTT) we have seen during the session.
-  void Update(QuicTime::Delta rtt, QuicTime::Delta delay_min);
+  // min_rtt: is the lowest delay (RTT) we have seen during the session.
+  // Returns true if slow start should be exited early, false otherwise.
+  bool UpdateAndMaybeExit(QuicTime::Delta rtt, QuicTime::Delta min_rtt);
 
-  // Returns true when we should exit slow start.
-  bool Exit();
-
-  bool started() const { return started_; }
+  // Whether slow start has started.
+  bool started() const {
+    return started_;
+  }
 
  private:
   const QuicClock* clock_;
+  // Whether the hybrid slow start has been started.
   bool started_;
   bool found_ack_train_;
   bool found_delay_;
   QuicTime round_start_;  // Beginning of each slow start round.
   // We need to keep track of the end sequence number of each RTT "burst".
   bool update_end_sequence_number_;
+  // TODO(ianswett): This should be redundant to the above, but was moved
+  // from TcpCubicSender to ensure the unit tests continued to pass.
   QuicPacketSequenceNumber sender_end_sequence_number_;
   QuicPacketSequenceNumber end_sequence_number_;  // End of slow start round.
-  QuicTime last_time_;  // Last time when the ACK spacing was close.
-  uint8 sample_count_;  // Number of samples to decide current RTT.
-  QuicTime::Delta current_rtt_;  // The minimum rtt of current round.
+  // Last time when the spacing between ack arrivals was less than 2 ms.
+  // Defaults to the beginning of the round.
+  QuicTime last_close_ack_pair_time_;
+  uint32 rtt_sample_count_;  // Number of rtt samples in the current round.
+  QuicTime::Delta current_min_rtt_;  // The minimum rtt of current round.
 
   DISALLOW_COPY_AND_ASSIGN(HybridSlowStart);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_