Introduce PushPullFIFO class and remove other FIFOs

third_party/WebKit/Source/platform/audio/PushPullFIFO.h

+// Copyright 2016 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 PushPullFIFO_h
+#define PushPullFIFO_h
+
+#include "platform/audio/AudioBus.h"
+#include "public/platform/WebCommon.h"
+#include "wtf/Allocator.h"
+
+namespace blink {
+
+class BLINK_PLATFORM_EXPORT PushPullFIFO {
+  USING_FAST_MALLOC(PushPullFIFO);
+  WTF_MAKE_NONCOPYABLE(PushPullFIFO);
+
+ public:
+  PushPullFIFO(unsigned numberOfChannels, size_t fifoLength);
+  ~PushPullFIFO();
+
+  // Pushing audio data is done by the WebAudio render-backing thread. The
+  // priority of this thread is lower than the actual audio device thread,
+  // thus the thread can be blocked when the audio device thread is pulling
+  // data from the FIFO.
+  void push(const AudioBus* inputBus);
+
+  // Pulling audio data is done by the audio device thread. This process must
+  // be non-blocking to ensure the glitch-less audio playback.

[o1ka, 2017/01/13 11:23:44]

What are the plans regarding thread safety?

[hongchan, 2017/01/13 23:29:23]

Giving a higher priority to pulling operation is one thing I have in mind.
WebAudio has this lock/trylock structure between the audio thread and the other
thread. So I am thinking about applying the same principle.

In short, when the data is being pulled the storage will be locked. The push
operation always have to wait for the pull operation.

+  void pull(AudioBus* outputBus, size_t framesToPull);
+
+  int framesAvailable() const { return std::max(0, m_framesAvailable); }
+  int length() const { return m_fifoLength; }
+  unsigned numberOfChannels() const { return m_fifoBus->numberOfChannels(); }
+  AudioBus* bus() { return m_fifoBus.get(); }
+
+ private:
+  RefPtr<AudioBus> m_fifoBus;
+
+  // The size of the FIFO.
+  const int m_fifoLength;
+
+  // The number of frames in the FIFO actually available for pulling.
+  int m_framesAvailable;
+
+  int m_indexRead;
+  int m_indexWrite;
+};
+
+}  // namespace blink
+
+#endif  // PushPullFIFO_h