Always PostTask device change notifications.

media/audio/mac/audio_manager_mac.cc

 // Copyright (c) 2012 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 "media/audio/mac/audio_manager_mac.h"
 
 #include <CoreAudio/AudioHardware.h>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 548 matching lines @@
     const AudioParameters& params,
     const std::string& device_id) {
   AudioDeviceID device = GetAudioDeviceIdByUId(false, device_id);
   if (device == kAudioObjectUnknown) {
     DLOG(ERROR) << "Failed to open output device: " << device_id;
     return NULL;
   }
 
   // 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;
     // Just use the current sample rate since we don't allow non-native sample
     // rates on OSX.
     current_sample_rate_ = params.sample_rate();
   }
 
   return new AUHALStream(this, params, device);
 }
@@ skipping 110 matching lines @@
   power_observer_.reset(new AudioPowerObserver());
 }
 
 void AudioManagerMac::ShutdownOnAudioThread() {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
   output_device_listener_.reset();
   power_observer_.reset();
 }
 
 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);
 
   if (current_sample_rate_ == new_sample_rate &&
       current_output_device_ == new_output_device)
     return;
 
   current_sample_rate_ = new_sample_rate;
   current_output_device_ = new_output_device;
   NotifyAllOutputDeviceChangeListeners();
@@ skipping 19 matching lines @@
 bool AudioManagerMac::ShouldDeferOutputStreamStart() {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
   return power_observer_->ShouldDeferOutputStreamStart();
 }
 
 AudioManager* CreateAudioManager(AudioLogFactory* audio_log_factory) {
   return new AudioManagerMac(audio_log_factory);
 }
 
 }  // namespace media