Do not switch best connection on the controlled side too frequently

webrtc/p2p/base/p2ptransportchannel.h

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 97 matching lines @@
   // From TransportChannel:
   int SendPacket(const char* data,
                  size_t len,
                  const rtc::PacketOptions& options,
                  int flags) override;
   int SetOption(rtc::Socket::Option opt, int value) override;
   bool GetOption(rtc::Socket::Option opt, int* value) override;
   int GetError() override { return error_; }
   bool GetStats(std::vector<ConnectionInfo>* stats) override;
 
-  const Connection* best_connection() const { return best_connection_; }
+  const Connection* selected_connection() const { return selected_connection_; }
   void set_incoming_only(bool value) { incoming_only_ = value; }
 
   // Note: This is only for testing purpose.
   // |ports_| should not be changed from outside.
   const std::vector<PortInterface*>& ports() { return ports_; }
 
   IceMode remote_ice_mode() const { return remote_ice_mode_; }
 
   // DTLS methods.
   bool IsDtlsActive() const override { return false; }
@@ skipping 72 matching lines @@
  private:
   rtc::Thread* thread() { return worker_thread_; }
   bool IsGettingPorts() { return allocator_session()->IsGettingPorts(); }
 
   // A transport channel is weak if the current best connection is either
   // not receiving or not writable, or if there is no best connection at all.
   bool weak() const;
   void UpdateConnectionStates();
   void RequestSort();
   void SortConnections();
-  void SwitchBestConnectionTo(Connection* conn);
+  void SwitchSelectedConnection(Connection* conn);
   void UpdateState();
   void HandleAllTimedOut();
   void MaybeStopPortAllocatorSessions();
   TransportChannelState ComputeState() const;
 
   Connection* GetBestConnectionOnNetwork(rtc::Network* network) const;
   bool CreateConnections(const Candidate& remote_candidate,
                          PortInterface* origin_port);
   bool CreateConnection(PortInterface* port,
                         const Candidate& remote_candidate,
@@ skipping 29 matching lines @@
   void OnSentPacket(const rtc::SentPacket& sent_packet);
   void OnReadyToSend(Connection* connection);
   void OnConnectionDestroyed(Connection *connection);
 
   void OnNominated(Connection* conn);
 
   void OnMessage(rtc::Message* pmsg) override;
   void OnSort();
   void OnCheckAndPing();
 
+  bool ShouldSwitchOnNominatedOrDataReceived(Connection* new_connection) const;

[pthatcher1, 2016/06/17 00:27:11]

I still think ShouldSwitchSelectedCandidate makes more sense.  We don't need why
to switch in the method name.

[honghaiz3, 2016/06/17 19:18:18]

Done.

+
   void PruneConnections();
-  Connection* best_nominated_connection() const;
+  Connection* selected_nominated_connection() const;
   bool IsBackupConnection(Connection* conn) const;
 
   Connection* FindConnectionToPing(int64_t now);
   Connection* FindOldestConnectionNeedingTriggeredCheck(int64_t now);
   // Between |conn1| and |conn2|, this function returns the one which should
   // be pinged first.
   Connection* SelectMostPingableConnection(Connection* conn1,
                                            Connection* conn2);
   // Select the connection which is Relay/Relay. If both of them are,
   // UDP relay protocol takes precedence.
@@ skipping 20 matching lines @@
   }
 
   PortAllocator* allocator_;
   rtc::Thread* worker_thread_;
   bool incoming_only_;
   int error_;
   std::vector<std::unique_ptr<PortAllocatorSession>> allocator_sessions_;
   std::vector<PortInterface *> ports_;
 
   // |connections_| is a sorted list with the first one always be the
-  // |best_connection_| when it's not nullptr. The combination of
+  // |selected_connection_| when it's not nullptr. The combination of
   // |pinged_connections_| and |unpinged_connections_| has the same
   // connections as |connections_|. These 2 sets maintain whether a
   // connection should be pinged next or not.
   std::vector<Connection *> connections_;
   std::set<Connection*> pinged_connections_;
   std::set<Connection*> unpinged_connections_;
 
-  Connection* best_connection_;
+  Connection* selected_connection_ = nullptr;
 
-  // Connection selected by the controlling agent. This should be used only
-  // at controlled side when protocol type is RFC5245.
-  Connection* pending_best_connection_;
+  // Connection most recently nominated by the controlling agent.
+  // This should be used only at the controlled side.
+  Connection* last_nominated_connection_ = nullptr;
+  // The connection on which the data was most recently received.
+  // Should only be used at the controlled side.
+  Connection* last_receiving_connection_ = nullptr;
+
   std::vector<RemoteCandidate> remote_candidates_;
   bool sort_dirty_;  // indicates whether another sort is needed right now
   bool had_connection_ = false;  // if connections_ has ever been nonempty
   typedef std::map<rtc::Socket::Option, int> OptionMap;
   OptionMap options_;
   std::string ice_ufrag_;
   std::string ice_pwd_;
   std::vector<IceParameters> remote_ice_parameters_;
   IceMode remote_ice_mode_;
   IceRole ice_role_;
   uint64_t tiebreaker_;
   IceGatheringState gathering_state_;
 
   int check_receiving_interval_;
   int64_t last_ping_sent_ms_ = 0;
   int weak_ping_interval_ = WEAK_PING_INTERVAL;
   TransportChannelState state_ = TransportChannelState::STATE_INIT;
   IceConfig config_;
   int last_sent_packet_id_ = -1;  // -1 indicates no packet was sent before.
 
   RTC_DISALLOW_COPY_AND_ASSIGN(P2PTransportChannel);
 };
 
 }  // namespace cricket
 
 #endif  // WEBRTC_P2P_BASE_P2PTRANSPORTCHANNEL_H_