Switch OnMoreData() to use AudioBus.

media/audio/mac/audio_output_mac.cc

Index: media/audio/mac/audio_output_mac.cc
diff --git a/media/audio/mac/audio_output_mac.cc b/media/audio/mac/audio_output_mac.cc
index 7f96735a495d6771b1e027740129cb7dcc95806a..daf84dabac8e7fea8b531f86efc86374f1165f35 100644
--- a/media/audio/mac/audio_output_mac.cc
+++ b/media/audio/mac/audio_output_mac.cc
@@ -53,7 +53,8 @@ PCMQueueOutAudioOutputStream::PCMQueueOutAudioOutputStream(
       should_swizzle_(false),
       should_down_mix_(false),
       stopped_event_(true /* manual reset */, false /* initial state */),
-      num_buffers_left_(kNumBuffers) {
+      num_buffers_left_(kNumBuffers),
+      audio_bus_(AudioBus::Create(params)) {
   // We must have a manager.
   DCHECK(manager_);
   // A frame is one sample across all channels. In interleaved audio the per
@@ -409,11 +410,25 @@ void PCMQueueOutAudioOutputStream::RenderCallback(void* p_this,
   // Adjust the number of pending bytes by subtracting the amount played.
   if (!static_cast<AudioQueueUserData*>(buffer->mUserData)->empty_buffer)
     audio_stream->pending_bytes_ -= buffer->mAudioDataByteSize;
+  uint32 filled = 0;
   uint32 capacity = buffer->mAudioDataBytesCapacity;
-  // TODO(sergeyu): Specify correct hardware delay for AudioBuffersState.
-  uint32 filled = source->OnMoreData(
-      reinterpret_cast<uint8*>(buffer->mAudioData), capacity,
-      AudioBuffersState(audio_stream->pending_bytes_, 0));
+  {
+    // Since RenderCallback may be reentrant, we need to ensure the AudioBus
+    // we're sharing is safe for this instance.  OnMoreData() offers no
+    // guarantee of thread safety as well.
+    base::AutoLock lock(audio_stream->audio_bus_lock_);

[Chris Rogers, 2012/08/28 22:32:05]

Please remove lock - it's not necessary from a thread-safety standpoint and
makes it harder to read the code.

[Chris Rogers, 2012/08/28 22:36:39]

To elaborate about removing the lock, the audio_bus_ is only used within the
RenderCallback() which itself is invoked on a single-thread.

[DaleCurtis, 2012/08/29 04:34:43]

Done.

+
+    AudioBus* audio_bus = audio_stream->audio_bus_.get();
+    DCHECK_EQ(
+        audio_bus->frames() * audio_stream->format_.mBytesPerFrame, capacity);
+    // TODO(sergeyu): Specify correct hardware delay for AudioBuffersState.
+    int frames_filled = source->OnMoreData(
+        audio_bus, AudioBuffersState(audio_stream->pending_bytes_, 0));
+    filled = frames_filled * audio_stream->format_.mBytesPerFrame;
+    audio_bus->ToInterleaved(
+        frames_filled, audio_stream->format_.mBitsPerChannel / 8,
+        buffer->mAudioData);
+  }
 
   // In order to keep the callback running, we need to provide a positive amount
   // of data to the audio queue. To simulate the behavior of Windows, we write