Defer OSX output stream Start() around system supend and resume.

media/audio/mac/audio_manager_mac.h

 // 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.
 
 #ifndef MEDIA_AUDIO_MAC_AUDIO_MANAGER_MAC_H_
 #define MEDIA_AUDIO_MAC_AUDIO_MANAGER_MAC_H_
 
 #include <CoreAudio/AudioHardware.h>
 #include <string>
 
@@ skipping 43 matching lines @@
 
   static bool GetDefaultOutputChannels(int* channels);
 
   static bool GetDeviceChannels(AudioDeviceID device,
                                 AudioObjectPropertyScope scope,
                                 int* channels);
 
   static int HardwareSampleRateForDevice(AudioDeviceID device_id);
   static int HardwareSampleRate();
 
+  // OSX has issues with starting streams as the sytem goes into suspend and
+  // immediately after it wakes up from resume.  See http://crbug.com/160920.
+  // As a workaround we delay Start() when it occurs after suspend and for a
+  // small amount of time after resume.
+  //
+  // Output streams should consult ShouldDeferOutputStreamStart() and if true
+  // check the value again after |kStartDelayInSecsForPowerEvents| has elapsed.
+  // If false, the stream may be started immediately.
+  enum { kStartDelayInSecsForPowerEvents = 1 };
+  bool ShouldDeferOutputStreamStart();
+
  protected:
   virtual ~AudioManagerMac();
 
   virtual AudioParameters GetPreferredOutputStreamParameters(
       const std::string& output_device_id,
       const AudioParameters& input_params) OVERRIDE;
 
  private:
   bool HasUnifiedDefaultIO();
 
   // Helper methods for constructing AudioDeviceListenerMac on the audio thread.
   void CreateDeviceListener();
   void DestroyDeviceListener();
 
   int ChooseBufferSize(int output_sample_rate);
 
   // Notify streams of a device change if the default output device or its
   // sample rate has changed, otherwise does nothing.
   void HandleDeviceChanges();
 
   scoped_ptr<AudioDeviceListenerMac> output_device_listener_;
 
   // Track the output sample-rate and the default output device
   // so we can intelligently handle device notifications only when necessary.
   int current_sample_rate_;
   AudioDeviceID current_output_device_;
 
   AggregateDeviceManager aggregate_device_manager_;
 
+  // Helper class which monitors power events to determine if output streams
+  // should defer Start() calls.  Required to workaround an OSX bug.  See
+  // http://crbug.com/160920 for more details.
+  class AudioPowerObserver;
+  scoped_ptr<AudioPowerObserver> power_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioManagerMac);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_MAC_AUDIO_MANAGER_MAC_H_