(Relanding) Restores larger output buffer size when output stream requiring smaller size is closed

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 <AudioUnit/AudioUnit.h>
 #include <CoreAudio/AudioHardware.h>
 #include <stddef.h>
 
 #include <list>
+#include <map>
 #include <memory>
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "media/audio/audio_manager_base.h"
 #include "media/audio/mac/audio_device_listener_mac.h"
 
 namespace media {
 
@@ skipping 74 matching lines @@
   // |size_was_changed| is set to true if the device's buffer size was changed
   // and |io_buffer_frame_size| contains the new buffer size.
   // Returns false if an error occurred.
   bool MaybeChangeBufferSize(AudioDeviceID device_id,
                              AudioUnit audio_unit,
                              AudioUnitElement element,
                              size_t desired_buffer_size,
                              bool* size_was_changed,
                              size_t* io_buffer_frame_size);
 
+  // Called by AUHALStream::Close() before releasing the stream.
+  // This method is a special contract between the real stream and the audio
+  // manager and it ensures that we only try to increase the IO buffer size
+  // for real streams and not for fake or mocked streams.
+  void PrepareForAttemptToIncreaseIOBufferSize(AudioDeviceID device_id);
+
   // Number of constructed output and input streams.
   size_t output_streams() const { return output_streams_.size(); }
   size_t low_latency_input_streams() const {
     return low_latency_input_streams_.size();
   }
   size_t basic_input_streams() const { return basic_input_streams_.size(); }
 
  protected:
   ~AudioManagerMac() override;
 
   AudioParameters GetPreferredOutputStreamParameters(
       const std::string& output_device_id,
       const AudioParameters& input_params) override;
 
  private:
   void InitializeOnAudioThread();
 
   int ChooseBufferSize(bool is_input, int sample_rate);
 
   // Notify streams of a device change if the default output device or its
   // sample rate has changed, otherwise does nothing.
   void HandleDeviceChanges();
 
+  // Returns true if any active input stream is using the specified |device_id|.
+  bool AudioDeviceIsUsedForInput(AudioDeviceID device_id);
+
+  // This method is called when an output stream has been released and it takes
+  // the given |device_id| and scans all active output streams that are
+  // using this id. The goal is to find a new (larger) I/O buffer size which
+  // can be applied to all active output streams since doing so will save
+  // system resources.
+  // Note that, it is only called if no input stream is also using the device.
+  // Example: two active output streams where #1 wants 1024 as buffer size but
+  // is using 256 since stream #2 wants it. Now, if stream #2 is closed down,
+  // the native I/O buffer size will be increased to 1024 instead of 256.
+  // Returns true if it was possible to increase the I/O buffer size and
+  // false otherwise.
+  // TODO(henrika): possibly extend the scheme to also take input streams into
+  // account.
+  bool IncreaseIOBufferSizeIfPossible(AudioDeviceID device_id);
+
   std::unique_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_;
 
   // 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;
   std::unique_ptr<AudioPowerObserver> power_observer_;
 
   // Tracks all constructed input and output streams.
   // TODO(alokp): We used to track these streams to close before destruction.
   // We no longer close the streams, so we may be able to get rid of these
   // member variables. They are currently used by MaybeChangeBufferSize().
   // Investigate if we can remove these.
   std::list<AudioInputStream*> basic_input_streams_;
   std::list<AUAudioInputStream*> low_latency_input_streams_;
   std::list<AUHALStream*> output_streams_;
 
+  // Maps device IDs and their corresponding actual (I/O) buffer sizes for
+  // all output streams using the specific device.
+  std::map<AudioDeviceID, size_t> output_io_buffer_size_map_;
+
+  // Device ID set bu the PrepareForAttemptToIncreaseIOBufferSize() method.
+  // Only modified by real audio output stream implementations, i.e., not
+  // fake audio output streams.
+  AudioDeviceID device_id_used_by_closing_output_stream_;
+
+  // Set to true in PrepareForAttemptToIncreaseIOBufferSize() to prepare for
+  // a possible modification of the native I/O buffer size. Set to false after
+  // an attempt to increase the I/O buffer size has finalized.
+  bool try_to_increase_io_buffer_size_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioManagerMac);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_MAC_AUDIO_MANAGER_MAC_H_