Fix segfault when PeerConnection is destroyed during stats collection.

webrtc/api/peerconnection.cc

 /*
  *  Copyright 2012 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 590 matching lines @@
   // Need to detach RTP senders/receivers from WebRtcSession,
   // since it's about to be destroyed.
   for (const auto& sender : senders_) {
     sender->internal()->Stop();
   }
   for (const auto& receiver : receivers_) {
     receiver->internal()->Stop();
   }
   // Destroy stats_ because it depends on session_.
   stats_.reset(nullptr);
+  stats_collector_->WaitForPendingRequest();

[hta-webrtc, 2016/12/16 14:05:31]

Doing waiting in a destructor makes me itchy. The destructor seems to be marked
"protected" in the .h files - is it possible to do the waiting in the function
that calls the destructor instead, and just assert that there are no pending
requests when you get to the destructor level?

There's another wait below (the Invoke()), where the same comments apply, so you
wouldn't make the destructor more irritating to me than it already is, but it's
nice to not cause excessive itches.

[hbos, 2016/12/16 14:34:52]

I'm afraid not, PeerConnectionInterface is reference counted, the only thing we
can be sure of is that we're on the signaling thread.

[hta-webrtc, 2016/12/17 19:51:30]

OK, the only thing that calls the destructor is the subclass constructed by
RefCounted<PeerConnection>..... but you have no real control over when the
refcount hits zero. Then this makes sense.

+  stats_collector_ = nullptr;
   // Now destroy session_ before destroying other members,
   // because its destruction fires signals (such as VoiceChannelDestroyed)
   // which will trigger some final actions in PeerConnection...
   session_.reset(nullptr);
   // port_allocator_ lives on the network thread and should be destroyed there.
   network_thread()->Invoke<void>(RTC_FROM_HERE,
                                  [this] { port_allocator_.reset(nullptr); });
 }
 
 bool PeerConnection::Initialize(
@@ skipping 1779 matching lines @@
 
 bool PeerConnection::StartRtcEventLog_w(rtc::PlatformFile file,
                                         int64_t max_size_bytes) {
   return event_log_->StartLogging(file, max_size_bytes);
 }
 
 void PeerConnection::StopRtcEventLog_w() {
   event_log_->StopLogging();
 }
 }  // namespace webrtc