Fix threading races on WebAudioSourceProviderImpl::provideInput

content/renderer/media/webaudiosourceprovider_impl.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/webaudiosourceprovider_impl.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "third_party/WebKit/public/web/WebAudioSourceProviderClient.h"
@@ skipping 69 matching lines @@
     sink_->SetVolume(volume_);
     if (state_ >= kStarted)
       sink_->Start();
     if (state_ >= kPlaying)
       sink_->Play();
   }
 }
 
 void WebAudioSourceProviderImpl::provideInput(
     const WebVector<float*>& audio_data, size_t number_of_frames) {
-  if (!bus_wrapper_ ||
-      static_cast<size_t>(bus_wrapper_->channels()) != audio_data.size()) {
-    bus_wrapper_ = media::AudioBus::CreateWrapper(audio_data.size());
-  }
-
-  bus_wrapper_->set_frames(number_of_frames);
-  for (size_t i = 0; i < audio_data.size(); ++i)
-    bus_wrapper_->SetChannelData(i, audio_data[i]);
-
   // Use a try lock to avoid contention in the real-time audio thread.
   AutoTryLock auto_try_lock(sink_lock_);
-  if (!auto_try_lock.locked() || state_ != kPlaying) {
+  if (auto_try_lock.locked() && state_ == kPlaying) {
+    if (!bus_wrapper_ ||
+        static_cast<size_t>(bus_wrapper_->channels()) != audio_data.size()) {
+      bus_wrapper_ = media::AudioBus::CreateWrapper(audio_data.size());
+    }
+
+    bus_wrapper_->set_frames(number_of_frames);
+    for (size_t i = 0; i < audio_data.size(); ++i)
+      bus_wrapper_->SetChannelData(i, audio_data[i]);
+  } else {
     // Provide silence if we failed to acquire the lock or the source is not
     // running.
     bus_wrapper_->Zero();

[Ken Russell (switch to Gerrit), 2013/09/04 17:09:36]

This looks wrong. If the trylock fails, then now, bus_wrapper_ might not have
been allocated here.

     return;
   }
 
   DCHECK(renderer_);
   DCHECK(client_);
   DCHECK_EQ(channels_, bus_wrapper_->channels());
   renderer_->Render(bus_wrapper_.get(), 0);
   bus_wrapper_->Scale(volume_);
 }
 
@@ skipping 50 matching lines @@
   channels_ = params.channels();
   sample_rate_ = params.sample_rate();
 
   if (client_) {
     // Inform WebKit about the audio stream format.
     client_->setFormat(channels_, sample_rate_);
   }
 }
 
 }  // namespace content