Add generic interfaces for the sinks of the media stream audio track

content/renderer/media/media_stream_audio_sink_owner.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/media_stream_audio_sink_owner.h"
+
+#include "content/public/renderer/media_stream_audio_sink.h"
+#include "media/audio/audio_parameters.h"
+
+namespace content {
+
+MediaStreamAudioSinkOwner::MediaStreamAudioSinkOwner(
+    MediaStreamAudioSink* sink)
+    : delegate_(sink) {
+}
+
+int MediaStreamAudioSinkOwner::OnData(const int16* audio_data,
+                                      int sample_rate,
+                                      int number_of_channels,
+                                      int number_of_frames,
+                                      const std::vector<int>& channels,
+                                      int audio_delay_milliseconds,
+                                      int current_volume,
+                                      bool need_audio_processing,
+                                      bool key_pressed) {
+  base::AutoLock lock(lock_);
+  if (delegate_) {
+    delegate_->OnData(audio_data,

[Alpha Left Google, 2013/12/02 19:11:38]

There should be a TODO to fix this. Delegate can spend long processing time on
the data. Doing this inside a lock is bad. Maybe take the pointer in a lock and
call OnData() outside the lock? I'm not sure but this definitely need a fix.

[no longer working on chromium, 2013/12/03 11:45:45]

This is old code and the change is from renaming:
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/m...

There are multiple reasons why we need to hold the lock for the whole section:
#1 When the sink goes away, we call RemoveSink() on the main render thread,
which set the delegate_ to NULL, but OnData() might be ongoing. we need to make
sure no more callback after RemoveSink().
#2 Avoiding too many reference count. We don't want to make all the sinks
reference counted to be able to avoid a lock here.
#3 It is true that delegate might spend some processing time, the drawback is
that it will block the main render thread a bit when the sink is removed from
the track, so it is not a big problem. From the real-time perspective, it is
fine to let the real-time thread to block other thread, but not the other way
around.

Anyway, I added a TODO to make the process quicker, though I am not sure if we
have another better option here.

+                      sample_rate,
+                      number_of_channels,
+                      number_of_frames);
+  }
+
+  return 0;
+}
+
+void MediaStreamAudioSinkOwner::OnSetFormat(
+    const media::AudioParameters& params) {
+  base::AutoLock lock(lock_);
+  if (delegate_)
+    delegate_->OnSetFormat(params);
+}
+
+void MediaStreamAudioSinkOwner::Reset() {
+  base::AutoLock lock(lock_);
+  delegate_ = NULL;
+}
+
+bool MediaStreamAudioSinkOwner::IsEqual(
+    const MediaStreamAudioSink* other) const {
+  DCHECK(other);
+  base::AutoLock lock(lock_);
+  return (other == delegate_);
+}
+
+bool MediaStreamAudioSinkOwner::IsEqual(
+    const PeerConnectionAudioSink* other) const {
+  DCHECK(other);
+  return false;
+}
+
+}  // namespace content