Adds AudioFifo class to Chrome media.

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 "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.
+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.
+  // Returns false if the allocated space is not sufficient.  Partial data is
+  // not written to the FIFO for this overflow case.
+  bool Push(const AudioBus* source);
+
+  // Consumes |frames_to_consume| audio frames from the FIFO and copies
+  // them to |destination|.
+  // Returns false if the FIFO does not contain |frames_to_consume| frames
+  // or if there is not sufficient space in |destination| to store the frames.
+  bool Consume(AudioBus* destination, int frames_to_consume);

[scherkus (not reviewing), 2012/09/06 13:53:57]

are callees expected to check their own size / frames_in_fifo() prior to calling
Consume()?

if so, should we crash instead of returning bool? it looks like it's being used
to signal two separate classes of errors (not enough in destination / not enough
in fifo)

In general I try to avoid "return a bool indicating success" functions because
people tend to forget to check the result :)

[henrika (OOO until Aug 14), 2012/09/07 14:10:37]

Are you suggesting that I modify to void and add CHECK() for these two failing
cases?

And yes, the user can either do the sanity check you list or go for it and check
the return value ;-)

Disussed off-line; will change.

+
+  // Empties the FIFO without deallocating any memory.
+  void Clear();
+
+  // Number of actual audio bus frames in the FIFO.
+  int frames_in_fifo() const { return frames_in_fifo_; }

[scherkus (not reviewing), 2012/09/06 13:53:57]

s/frames_in_fifo/frames/ ?

we're using a FIFO object so not sure why we need to repeat the _in_fifo() bit

[henrika (OOO until Aug 14), 2012/09/07 14:10:37]

LOL, that's my melody as well but not all reviewers like the initial proposal
since it could be mixed up with the max number of frames it can contain ;-)

I'll be happy to change. Done.

+
+ private:
+  int max_frames() const { return max_frames_in_fifo_; }
+
+  // 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_in_fifo_;
+
+  // Number of actual elements in the FIFO.
+  int frames_in_fifo_;
+
+  // 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_