Reduce locking when collecting receive statistics.

webrtc/modules/rtp_rtcp/source/receive_statistics_impl.h

 /*
  *  Copyright (c) 2013 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.
  */
 
 #ifndef WEBRTC_MODULES_RTP_RTCP_SOURCE_RECEIVE_STATISTICS_IMPL_H_
 #define WEBRTC_MODULES_RTP_RTCP_SOURCE_RECEIVE_STATISTICS_IMPL_H_
 
 #include "webrtc/modules/rtp_rtcp/include/receive_statistics.h"
 
 #include <algorithm>
 #include <map>
 #include <vector>
 
 #include "webrtc/rtc_base/criticalsection.h"
 #include "webrtc/rtc_base/rate_statistics.h"
 #include "webrtc/system_wrappers/include/ntp_time.h"
 
 namespace webrtc {
 
 class StreamStatisticianImpl : public StreamStatistician {
  public:
-  StreamStatisticianImpl(Clock* clock,
+  StreamStatisticianImpl(uint32_t ssrc,
+                         Clock* clock,
                          RtcpStatisticsCallback* rtcp_callback,
                          StreamDataCountersCallback* rtp_callback);
   virtual ~StreamStatisticianImpl() {}
 
   bool GetStatistics(RtcpStatistics* statistics, bool reset) override;
   void GetDataCounters(size_t* bytes_received,
                        uint32_t* packets_received) const override;
   void GetReceiveStreamDataCounters(
       StreamDataCounters* data_counters) const override;
   uint32_t BitrateReceived() const override;
   bool IsRetransmitOfOldPacket(const RTPHeader& header,
                                int64_t min_rtt) const override;
   bool IsPacketInOrder(uint16_t sequence_number) const override;
 
   void IncomingPacket(const RTPHeader& rtp_header,
                       size_t packet_length,
                       bool retransmitted);
   void FecPacketReceived(const RTPHeader& header, size_t packet_length);
   void SetMaxReorderingThreshold(int max_reordering_threshold);
   virtual void LastReceiveTimeNtp(uint32_t* secs, uint32_t* frac) const;
 
  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.
   uint32_t jitter_q4_;
   uint32_t cumulative_loss_;
   uint32_t jitter_q4_transmission_time_offset_;
 
   int64_t last_receive_time_ms_;
   NtpTime last_receive_time_ntp_;
   uint32_t last_received_timestamp_;
@@ skipping 54 matching lines @@
 
   Clock* const clock_;
   rtc::CriticalSection receive_statistics_lock_;
   StatisticianImplMap statisticians_;
 
   RtcpStatisticsCallback* rtcp_stats_callback_;
   StreamDataCountersCallback* rtp_stats_callback_;
 };
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_RECEIVE_STATISTICS_IMPL_H_