Do not switch best connection on the controlled side too frequently

webrtc/p2p/base/p2ptransportchannel.h

Index: webrtc/p2p/base/p2ptransportchannel.h
diff --git a/webrtc/p2p/base/p2ptransportchannel.h b/webrtc/p2p/base/p2ptransportchannel.h
index ada3ecfb8bb2deeb6bc5d9120eb1647d7cd1a1da..7f492537ddef2928b66baa8dc6c9df375fade9ad 100644
--- a/webrtc/p2p/base/p2ptransportchannel.h
+++ b/webrtc/p2p/base/p2ptransportchannel.h
@@ -115,7 +115,7 @@ class P2PTransportChannel : public TransportChannelImpl,
   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.
@@ -208,7 +208,7 @@ class P2PTransportChannel : public TransportChannelImpl,
   void UpdateConnectionStates();
   void RequestSort();
   void SortConnections();
-  void SwitchBestConnectionTo(Connection* conn);
+  void SwitchSelectedConnection(Connection* conn);
   void UpdateState();
   void HandleAllTimedOut();
   void MaybeStopPortAllocatorSessions();
@@ -258,8 +258,24 @@ class P2PTransportChannel : public TransportChannelImpl,
   void OnSort();
   void OnCheckAndPing();
 
+  // Compares two connections based on the connection states
+  // (writable/receiving/connected), nomination states, last data received time,
+  // and static preferences. Does not include latency. Used by both sorting
+  // and ShouldSwitchConnection().
+  // Returns a positive value if |a| is better than |b|.
+  int CompareConnections(const cricket::Connection* a,
+                         const cricket::Connection* b) const;
+  // This is similar to CompareConnections but excludes the connection states
+  // from the comparison criteria. It is used when determining whether a
+  // connection need to be pruned.

[pthatcher1, 2016/06/21 07:16:53]

need to be => needs to be

[honghaiz3, 2016/06/22 08:03:16]

Done.

+  // Returns a positive value if |a| is better than |b|

[Taylor Brandstetter, 2016/06/21 18:33:26]

Missing period.

[honghaiz3, 2016/06/22 08:03:16]

Done.

+  int CompareConnectionsBase(const cricket::Connection* a,

[Taylor Brandstetter, 2016/06/21 18:33:26]

I think this method can be removed. But if it's kept in, it should have a better
name, such as CompareConnectionsIgnoringWriteState.

[honghaiz3, 2016/06/22 08:03:16]

Done.

+                             const cricket::Connection* b) const;
+  // Returns true if the new_connection should be selected for transmission.
+  bool ShouldSwitchConnection(Connection* new_connection) const;
+
   void PruneConnections();
-  Connection* best_nominated_connection() const;
+  Connection* selected_nominated_connection() const;
   bool IsBackupConnection(Connection* conn) const;
 
   Connection* FindConnectionToPing(int64_t now);
@@ -300,7 +316,7 @@ class P2PTransportChannel : public TransportChannelImpl,
   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.
@@ -308,11 +324,8 @@ class P2PTransportChannel : public TransportChannelImpl,
   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_;
   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