Avoid race in Call destructor

webrtc/call/call.cc

 /*
  *  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.
  */
 
@@ skipping 247 matching lines @@
   module_process_thread_->RegisterModule(congestion_controller_.get());
   pacer_thread_->RegisterModule(congestion_controller_->pacer());
   pacer_thread_->RegisterModule(
       congestion_controller_->GetRemoteBitrateEstimator(true));
   pacer_thread_->Start();
 }
 
 Call::~Call() {
   RTC_DCHECK(!remb_.InUse());
   RTC_DCHECK(configuration_thread_checker_.CalledOnValidThread());
-  UpdateSendHistograms();
-  UpdateReceiveHistograms();
   RTC_CHECK(audio_send_ssrcs_.empty());
   RTC_CHECK(video_send_ssrcs_.empty());
   RTC_CHECK(video_send_streams_.empty());
   RTC_CHECK(audio_receive_ssrcs_.empty());
   RTC_CHECK(video_receive_ssrcs_.empty());
   RTC_CHECK(video_receive_streams_.empty());
 
   pacer_thread_->Stop();
   pacer_thread_->DeRegisterModule(congestion_controller_->pacer());
   pacer_thread_->DeRegisterModule(
       congestion_controller_->GetRemoteBitrateEstimator(true));
   module_process_thread_->DeRegisterModule(congestion_controller_.get());
   module_process_thread_->DeRegisterModule(call_stats_.get());
   module_process_thread_->Stop();
   call_stats_->DeregisterStatsObserver(congestion_controller_.get());
+
+  // Only update histograms after process threads have been shut down, so that
+  // they won't try to concurrently update stats.
+  UpdateSendHistograms();
+  UpdateReceiveHistograms();
+
   Trace::ReturnTrace();
 }
 
 void Call::UpdateSendHistograms() {
   if (num_bitrate_updates_ == 0 || first_packet_sent_ms_ == -1)
     return;
   int64_t elapsed_sec =
       (clock_->TimeInMilliseconds() - first_packet_sent_ms_) / 1000;
   if (elapsed_sec < metrics::kMinRunTimeInSeconds)
     return;
@@ skipping 578 matching lines @@
   // thread. Then this check can be enabled.
   // RTC_DCHECK(!configuration_thread_checker_.CalledOnValidThread());
   if (RtpHeaderParser::IsRtcp(packet, length))
     return DeliverRtcp(media_type, packet, length);
 
   return DeliverRtp(media_type, packet, length, packet_time);
 }
 
 }  // namespace internal
 }  // namespace webrtc