Introduce PushPullFIFO class and remove other FIFOs

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

Index: third_party/WebKit/Source/platform/audio/PushPullFIFO.h
diff --git a/third_party/WebKit/Source/platform/audio/PushPullFIFO.h b/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
new file mode 100644
index 0000000000000000000000000000000000000000..22ff551b2aecdf7309932b8ff2d68febc9501c57
--- /dev/null
+++ b/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
@@ -0,0 +1,44 @@
+// 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 "wtf/Allocator.h"
+
+namespace blink {
+
+class PushPullFIFO {
+  USING_FAST_MALLOC(PushPullFIFO);
+  WTF_MAKE_NONCOPYABLE(PushPullFIFO);
+
+ public:
+  PushPullFIFO(unsigned numberOfChannels, size_t length);
+  ~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.
+  void pull(AudioBus* outputBus, size_t framesToPull);

[o1ka, 2017/01/09 14:09:03]

How do you plan to ensure thread safety?

[hongchan, 2017/01/09 21:53:16]

I believe this FIFO should give the higher priority to the pulling operation so
we can ensure the exclusive access to the audio device callback. I added a lock
in ::pull() method.

+
+  size_t numberOfFrames() const { return m_numberOfFrames; }
+
+ private:
+  RefPtr<AudioBus> m_dataBus;

[Raymond Toy, 2017/01/06 22:22:03]

Maybe m_fifoDataBus?

[hongchan, 2017/01/09 21:53:16]

Done.

+
+  size_t m_length;
+  size_t m_numberOfFrames;
+  size_t m_indexRead;
+  size_t m_indexWrite;

[Raymond Toy, 2017/01/06 22:22:03]

Please document what all of these mean.  If m_length is the length of the FIFO,
then maybe m_fifoSize is a better name?

[hongchan, 2017/01/09 21:53:16]

Done. 

AudioBus uses the term 'length'. The FIFO is based on AudioBus, so I wanted to
make it consistent. Perhaps you can say the overall "size" is numberOfChannel *
length.

+};
+
+}  // namespace blink
+
+#endif  // PushPullFIFO_h