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..1cf7b6aa930521e9f321afcd20a387ec22fb72d6
--- /dev/null
+++ b/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
@@ -0,0 +1,85 @@
+// Copyright 2017 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 {
+
+// A configuration data container for PushPullFIFO unit test.
+struct PushPullFIFOStateForTest {
+  const size_t fifoLength;
+  const unsigned numberOfChannels;
+  const size_t framesAvailable;
+  const size_t indexRead;
+  const size_t indexWrite;
+  const unsigned overflowCount;
+  const unsigned underflowCount;
+};
+
+// Maximum FIFO length. (512 RQs)
+static const size_t kMaxFIFOLength = 65536;

[o1ka, 2017/02/02 16:30:25]

Shouldn't the constant should only be declared here, and defined in cpp?
Otherwise every file including it has its personal copy.
Also, blink namespace seems to be too broad for a global constant.
Make it a static member of PushPullFIFO?

[hongchan, 2017/02/02 19:55:23]

Done.

+
+// PushPullFIFO class is an intermediate audio sample storage between
+// Blink-WebAudio and the renderer. The renderer's hardware callback buffer size
+// varies on the platform, but the WebAudio always renders 128 frames (render
+// quantum, RQ) thus FIFO is needed to handle the general case.
+class BLINK_PLATFORM_EXPORT PushPullFIFO {
+  USING_FAST_MALLOC(PushPullFIFO);
+  WTF_MAKE_NONCOPYABLE(PushPullFIFO);
+
+ public:
+  // |fifoLength| cannot exceed |kMaxFIFOLength|. Otherwise it crashes.
+  explicit PushPullFIFO(unsigned numberOfChannels, size_t fifoLength);
+  ~PushPullFIFO();
+
+  // By design, the length of |inputBus| is 128 frames.
+  //  - The |inputBus| length is 128 frames (1 RQ), fixed.

[o1ka, 2017/02/02 16:30:24]

Duplication of the previous line?

[hongchan, 2017/02/02 19:55:23]

Done.

+  //  - In case of overflow (FIFO full while push), the existing frames in FIFO
+  //    will be overwritten and |indexRead| will be forcibly moved to
+  //    |indexWrite| to avoid reading overwritten frames.
+  void push(const AudioBus* inputBus);
+
+  // Pulling |framesRequested| by the audio device thread.
+  //  - If |framesRequested| is bigger than the length of |outputBus|, it
+  //    violates SECURITY_CHECK().
+  //  - If |framesRequested| is bigger than FIFO length, it violates
+  //    SECURITY_CHECK().
+  //  - In case of underflow (FIFO empty while pull), the remaining space in the
+  //    requested output bus will be filled with silence. Thus it will fulfill
+  //    the request from the consumer without causing error, but with a glitch.
+  void pull(AudioBus* outputBus, size_t framesRequested);
+
+  size_t framesAvailable() const { return m_framesAvailable; }
+  size_t length() const { return m_fifoLength; }
+  unsigned numberOfChannels() const { return m_fifoBus->numberOfChannels(); }
+  AudioBus* bus() const { return m_fifoBus.get(); }
+
+  // For unit test. Get the current configuration that consists of FIFO length,
+  // number of channels, read/write index position and under/overflow count.
+  const PushPullFIFOStateForTest getStateForTest() const;
+
+ private:
+  // The size of the FIFO.
+  const size_t m_fifoLength = 0;
+
+  RefPtr<AudioBus> m_fifoBus;
+
+  // The number of frames in the FIFO actually available for pulling.
+  size_t m_framesAvailable;
+
+  size_t m_indexRead;
+  size_t m_indexWrite;
+
+  unsigned m_overflowCount;
+  unsigned m_underflowCount;
+};
+
+}  // namespace blink
+
+#endif  // PushPullFIFO_h