Add WebThread in AudioDestination to support AudioWorkletThread

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
index 2341372f35ab452fb8814dc22208ff3c24e9cd87..ca8f96d0c8a8e7a5eb6fb7232f58935925b22bf4 100644
--- a/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
+++ b/third_party/WebKit/Source/platform/audio/PushPullFIFO.h
@@ -8,6 +8,7 @@
 #include "platform/audio/AudioBus.h"
 #include "public/platform/WebCommon.h"
 #include "wtf/Allocator.h"
+#include "wtf/ThreadingPrimitives.h"
 
 namespace blink {
 
@@ -26,6 +27,14 @@ struct PushPullFIFOStateForTest {
 // 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.
+//
+// Note that this object is concurrently accessed by two threads; WebAudio
+// rendering thread (WebThread) in Blink and the audio device thread
+// (AudioDeviceThread) from the media renderer. The push/pull operations touch
+// most of variables in the class (m_indexWrite, m_indexRead, m_framesAvailable,
+// and m_fifoBus) so the thread safety must be handled with care.
+//
+// TODO(hongchan): add a unit test for multi-thread access.
 class BLINK_PLATFORM_EXPORT PushPullFIFO {
   USING_FAST_MALLOC(PushPullFIFO);
   WTF_MAKE_NONCOPYABLE(PushPullFIFO);
@@ -38,7 +47,7 @@ class BLINK_PLATFORM_EXPORT PushPullFIFO {
   explicit PushPullFIFO(unsigned numberOfChannels, size_t fifoLength);
   ~PushPullFIFO();
 
-  // Pushes the rendered frames by WebAudio engine.
+  // Pushes the rendered frames by WebAudio rendering thread.
   //  - The |inputBus| length is 128 frames (1 render quantum), fixed.
   //  - In case of overflow (FIFO full while push), the existing frames in FIFO
   //    will be overwritten and |indexRead| will be forcibly moved to
@@ -55,16 +64,20 @@ class BLINK_PLATFORM_EXPORT PushPullFIFO {
   //    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 framesAvailable() const;
   size_t length() const { return m_fifoLength; }
   unsigned numberOfChannels() const { return m_fifoBus->numberOfChannels(); }
-  AudioBus* bus() const { return m_fifoBus.get(); }
+  AudioBus* getFIFOBusForTest() const;
 
   // 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:
+  // This lock protects all members in this class from being accessed by two

[o1ka, 2017/03/30 13:17:05]

This is technically not quite correct: see length()/m_fifoLength (which is const
so no need to protect)

[hongchan, 2017/03/30 18:36:00]

Done.

+  // threads simultaneously.
+  mutable Mutex m_threadMutex;

[o1ka, 2017/03/30 13:17:05]

I'm not sure if this rename is useful.

[hongchan, 2017/03/30 18:36:00]

Done.

+
   // The size of the FIFO.
   const size_t m_fifoLength = 0;