Fix threading races on WebAudioSourceProviderImpl::provideInput

content/renderer/media/webaudiosourceprovider_impl.cc

Index: content/renderer/media/webaudiosourceprovider_impl.cc
diff --git a/content/renderer/media/webaudiosourceprovider_impl.cc b/content/renderer/media/webaudiosourceprovider_impl.cc
index b722a33af4c18e3073fcea36576f1775234a440e..52501f0f276236b109be3eba085ee63608babba6 100644
--- a/content/renderer/media/webaudiosourceprovider_impl.cc
+++ b/content/renderer/media/webaudiosourceprovider_impl.cc
@@ -87,18 +87,18 @@ void WebAudioSourceProviderImpl::setClient(
 
 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.