Restores larger output buffer size when output stream requiring smaller size is closed

media/audio/mac/audio_auhal_mac.h

 // 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.
 //
 // Implementation notes:
 //
 // - It is recommended to first acquire the native sample rate of the default
 //   output device and then use the same rate when creating this object.
 //   Use AudioManagerMac::HardwareSampleRate() to retrieve the sample rate.
 // - Calling Close() also leads to self destruction.
 // - The latency consists of two parts:
 //   1) Hardware latency, which includes Audio Unit latency, audio device
 //      latency;
 //   2) The delay between the moment getting the callback and the scheduled time
 //      stamp that tells when the data is going to be played out.
 //
 #ifndef MEDIA_AUDIO_MAC_AUDIO_AUHAL_MAC_H_
 #define MEDIA_AUDIO_MAC_AUDIO_AUHAL_MAC_H_
 
 #include <AudioUnit/AudioUnit.h>
 #include <CoreAudio/CoreAudio.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 
+#include "base/atomicops.h"
 #include "base/cancelable_callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "media/audio/audio_io.h"
 #include "media/base/audio_parameters.h"
 
 namespace media {
 
@@ skipping 44 matching lines @@
   // Implementation of AudioOutputStream.
   bool Open() override;
   void Close() override;
   void Start(AudioSourceCallback* callback) override;
   void Stop() override;
   void SetVolume(double volume) override;
   void GetVolume(double* volume) override;
 
   AudioDeviceID device_id() const { return device_; }
   size_t requested_buffer_size() const { return number_of_frames_; }
+  size_t actual_buffer_size() const {
+    return base::subtle::Acquire_Load(&actual_io_buffer_frame_size_);
+  }
+  AudioUnit audio_unit() const { return audio_unit_; }
 
  private:
   // AUHAL callback.
   static OSStatus InputProc(void* user_data,
                             AudioUnitRenderActionFlags* flags,
                             const AudioTimeStamp* time_stamp,
                             UInt32 bus_number,
                             UInt32 number_of_frames,
                             AudioBufferList* io_data);
 
@@ skipping 37 matching lines @@
   // Called from the dtor and when the stream is reset.
   void ReportAndResetStats();
 
   // Our creator, the audio manager needs to be notified when we close.
   AudioManagerMac* const manager_;
 
   const AudioParameters params_;
   // For convenience - same as in params_.
   const int output_channels_;
 
-  // Buffer-size.
+  // Size of audio buffer requested at construction. The actual buffer size
+  // is given by |actual_io_buffer_frame_size_| and it can differ from the
+  // requested size.
   const size_t number_of_frames_;
 
+  // Size of I/O buffers measured in number of audio frames. Default value is
+  // 512 but we always try to set it to a vaule as close as possible to
+  // |number_of_frames_|. It might not be possible to match the requested size,
+  // especially not if the utilized device is used by other streams as well.
+  // This value will be the same as |number_of_frames_requested_| but they are
+  // used for different purpuses and updated at different times.
+  // The member is read by the audio manager on the main browser thread
+  // (CrBrowserMain) and modified by this class on the Core Audio I/O thread.
+  base::subtle::Atomic32 actual_io_buffer_frame_size_;
+
   // Stores the number of frames that we actually get callbacks for.
   // This may be different from what we ask for, so we use this for stats in
   // order to understand how often this happens and what are the typical values.
   size_t number_of_frames_requested_;
 
   // Pointer to the object that will provide the audio samples.
   AudioSourceCallback* source_;
 
   // Protects |source_|.  Necessary since Render() calls seem to be in flight
   // when |audio_unit_| is supposedly stopped.  See http://crbug.com/178765.
@@ skipping 53 matching lines @@
   // Used to make sure control functions (Start(), Stop() etc) are called on the
   // right thread.
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(AUHALStream);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_MAC_AUDIO_AUHAL_MAC_H_