Reduce locking when collecting receive statistics.

webrtc/modules/rtp_rtcp/source/receive_statistics_impl.h

Index: webrtc/modules/rtp_rtcp/source/receive_statistics_impl.h
diff --git a/webrtc/modules/rtp_rtcp/source/receive_statistics_impl.h b/webrtc/modules/rtp_rtcp/source/receive_statistics_impl.h
index 1256562d7d12c4d8148881afa28220104486bf69..6948dd6f6bfeb7be7f62c19cddab27be4bebc0da 100644
--- a/webrtc/modules/rtp_rtcp/source/receive_statistics_impl.h
+++ b/webrtc/modules/rtp_rtcp/source/receive_statistics_impl.h
@@ -25,7 +25,8 @@ namespace webrtc {
 
 class StreamStatisticianImpl : public StreamStatistician {
  public:
-  StreamStatisticianImpl(Clock* clock,
+  StreamStatisticianImpl(uint32_t ssrc,
+                         Clock* clock,
                          RtcpStatisticsCallback* rtcp_callback,
                          StreamDataCountersCallback* rtp_callback);
   virtual ~StreamStatisticianImpl() {}
@@ -49,18 +50,20 @@ class StreamStatisticianImpl : public StreamStatistician {
 
  private:
   bool InOrderPacketInternal(uint16_t sequence_number) const;
-  RtcpStatistics CalculateRtcpStatistics();
+  RtcpStatistics CalculateRtcpStatistics()
+      EXCLUSIVE_LOCKS_REQUIRED(stream_lock_);
   void UpdateJitter(const RTPHeader& header, NtpTime receive_time);
-  void UpdateCounters(const RTPHeader& rtp_header,
-                      size_t packet_length,
-                      bool retransmitted);
-  void NotifyRtpCallback() LOCKS_EXCLUDED(stream_lock_);
-  void NotifyRtcpCallback() LOCKS_EXCLUDED(stream_lock_);
-
+  StreamDataCounters UpdateCounters(const RTPHeader& rtp_header,
+                                    size_t packet_length,
+                                    bool retransmitted);
+  void NotifyRtpCallback(const StreamDataCounters&)
+      LOCKS_EXCLUDED(stream_lock_);
+  void NotifyRtcpCallback(const RtcpStatistics&) LOCKS_EXCLUDED(stream_lock_);

[sprang_webrtc, 2017/08/14 09:43:06]

Nit: These don't seem to be very useful anymore, can we just add a guarded_by to
the callbacks pointers and call them directly?

[danilchap, 2017/08/14 10:45:32]

Checked documentation for LOCKS_EXCLUDED - it doesn't apply here.
so removing it together with the functions.

unfortunately I'm not aware of GUARDED_BY-like macro to annotate lock should NOT
be held when accessing a variable.

[sprang_webrtc, 2017/08/14 11:25:38]

Ah, shoot. Just assumed there was.

+
+  const uint32_t ssrc_;
   Clock* const clock_;
   rtc::CriticalSection stream_lock_;
   RateStatistics incoming_bitrate_;
-  uint32_t ssrc_;
   int max_reordering_threshold_;  // In number of packets or sequence numbers.
 
   // Stats on received RTP packets.