Add Mac OS X synchronized audio I/O back-end

media/base/audio_fifo.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_BASE_AUDIO_FIFO_H_
 #define MEDIA_BASE_AUDIO_FIFO_H_
 
+#include "base/atomicops.h"
 #include "media/base/audio_bus.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 // First-in first-out container for AudioBus elements.
 // The maximum number of audio frames in the FIFO is set at construction and
 // can not be extended dynamically.  The allocated memory is utilized as a
 // ring buffer.
+// This class is thread-safe in the limited sense that one thread may call
+// Push(), while a second thread calls Consume().
 class MEDIA_EXPORT AudioFifo {
  public:
   // Creates a new AudioFifo and allocates |channels| of length |frames|.
   AudioFifo(int channels, int frames);
   virtual ~AudioFifo();
 
   // Pushes all audio channel data from |source| to the FIFO.
   // Push() will crash if the allocated space is insufficient.
   void Push(const AudioBus* source);
 
   // Consumes |frames_to_consume| audio frames from the FIFO and copies
   // them to |destination| starting at position |start_frame|.
   // Consume() will crash if the FIFO does not contain |frames_to_consume|
   // frames or if there is insufficient space in |destination| to store the
   // frames.
   void Consume(AudioBus* destination, int start_frame, int frames_to_consume);
 
   // Empties the FIFO without deallocating any memory.
   void Clear();
 
   // Number of actual audio frames in the FIFO.
-  int frames() const { return frames_; }
+  int frames() const;
+
+  int max_frames() const { return max_frames_; }
 
  private:
-  int max_frames() const { return max_frames_; }
-
   // The actual FIFO is an audio bus implemented as a ring buffer.
   scoped_ptr<AudioBus> audio_bus_;
 
   // Maximum number of elements the FIFO can contain.
   // This value is set by |frames| in the constructor.
   const int max_frames_;
 
   // Number of actual elements in the FIFO.
-  int frames_;
+  volatile base::subtle::Atomic32 frames_pushed_;
+  volatile base::subtle::Atomic32 frames_consumed_;
 
   // Current read position.
   int read_pos_;
 
   // Current write position.
   int write_pos_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioFifo);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_FIFO_H_