Always PostTask device change notifications.

media/audio/mac/audio_manager_mac.cc

Index: media/audio/mac/audio_manager_mac.cc
diff --git a/media/audio/mac/audio_manager_mac.cc b/media/audio/mac/audio_manager_mac.cc
index 79ebe609ea9f4daba77e89c0dcc4354e5bb3c0e5..c24e9a50d45c5e61d38881f07a63124304a63e9b 100644
--- a/media/audio/mac/audio_manager_mac.cc
+++ b/media/audio/mac/audio_manager_mac.cc
@@ -566,8 +566,9 @@ AudioOutputStream* AudioManagerMac::MakeLowLatencyOutputStream(
 
   // Lazily create the audio device listener on the first stream creation.
   if (!output_device_listener_) {
-    output_device_listener_.reset(new AudioDeviceListenerMac(base::Bind(
-        &AudioManagerMac::HandleDeviceChanges, base::Unretained(this))));
+    output_device_listener_.reset(

[wolenetz, 2014/03/06 16:01:42]

nit: add comment about why BTCL is required here vs conditional post-task.

[DaleCurtis, 2014/03/06 19:27:37]

Done.

+        new AudioDeviceListenerMac(BindToCurrentLoop(base::Bind(

[wolenetz, 2014/03/06 16:01:42]

I'm not too familiar with audio pipeline. Is it possible for the callback task
posted by AudioDeviceListenerMac to outlive this manager (in the path where the
listener previously called HandeDeviceChanges() vs the new path where it posts a
task to the method but possibly this manager is deleted before the task
execution is scheduled)? I suspect not, given the predominance of manager code
conditionally post-tasking within the manager to itself, but if so, use weak
pointer?

[DaleCurtis, 2014/03/06 19:27:37]

No, in most cases AM shutdown blocks on the audio thread shutdown. However on
OSX, tasks are just dropped since the UI loop has already stopped running by the
time this class is destructed.  See the comment in AudioManagerBase::Shutdown()

+            &AudioManagerMac::HandleDeviceChanges, base::Unretained(this)))));
     // Only set the current output device for the default device.
     if (device_id == AudioManagerBase::kDefaultDeviceId || device_id.empty())
       current_output_device_ = device;
@@ -698,13 +699,8 @@ void AudioManagerMac::ShutdownOnAudioThread() {
 }
 
 void AudioManagerMac::HandleDeviceChanges() {
-  if (!GetTaskRunner()->BelongsToCurrentThread()) {
-    GetTaskRunner()->PostTask(FROM_HERE, base::Bind(
-        &AudioManagerMac::HandleDeviceChanges, base::Unretained(this)));
-    return;
-  }
-
-  int new_sample_rate = HardwareSampleRate();
+  DCHECK(GetTaskRunner()->BelongsToCurrentThread());
+  const int new_sample_rate = HardwareSampleRate();
   AudioDeviceID new_output_device;
   GetDefaultOutputDevice(&new_output_device);